ICSE Solutions for Class 10 Mathematics

ICSE Solutions for Class 10 Mathematics

Get ICSE Solutions for Class 10 Mathematics for ICSE Board Examinations on ICSESolutions.com. We provide step by step Solutions for ICSE Mathematics Class 10 Solutions Pdf. You can download the Class 10 Maths ICSE Textbook Solutions with Free PDF download option.

ICSE Solutions for Class 10 Mathematics

For More Resources

New Simplified Middle School Chemistry Class 10 ICSE Solutions

New Simplified Middle School Chemistry Class 10 ICSE Solutions

New Simplified Middle School Chemistry Class 10 ICSE Solutions (Dr. Viraf J.Dalal, Allied Publishers)

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

Viraf J Dalal Chemistry Class 10 Solutions and Answers

Simplified ChemistryEnglishMathsPhysicsChemistryBiology

  1. Periodic Table – Periodic Properties and Variations of Properties
  2. Chemical Bonding
  3. A: Acids, Bases and Salts
    B: Analytical Chemistry Use of Ammonium and Sodium Hydroxide
  4. Mole Concept and Stoichiometry
    A: Gay Lussac’s Law-Avogadro’s Law-Mole concept
    B: Percentage Composition – Empirical and Molecular formula Calculations Based on Chemical Equations
  5. Electrolysis
  6. Metallurgy
  7. Study of Compounds
    A: Hydrogen Chloride
    B: Ammonia
    C: Nitric Acid
    D: Sulphuric Acid
  8. Organic Chemistry
  9. Practical Chemistry

Give Reasons – State Observations

For More Resources

A New Approach to ICSE Physics Part 2 Class 10 Solutions

A New Approach to ICSE Physics Part 2 Class 10 Solutions

A New Approach to ICSE Physics Part 2 Class 10 Solutions (Goyal Brothers Prakashan)

More Resources

Selina Concise Chemistry Class 8 ICSE Solutions – Physical and Chemical Changes

Selina Concise Chemistry Class 8 ICSE Solutions – Physical and Chemical Changes

ICSE Solutions  Selina ICSE Solutions  ML Aggarwal Solutions

ICSESolutions.com provides step by step solutions for Selina Concise ICSE Solutions for Class 8 Chemistry Chapter 2 Physical and Chemical Changes. You can download the Selina Concise Chemistry ICSE Solutions for Class 8 with Free PDF download option. Selina Publishers Concise Chemistry for Class 8 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

Selina Class 8 Chemistry ICSE SolutionsPhysicsBiologyMathsGeographyHistory & Civics

Selina Concise ICSE Solutions for Class 8 Chemistry Chapter 2 Physical and Chemical Changes

Exercise

Question 1.
Define:
(a) a physical change, (b) a chemical change.
Answer:
(a) Physical Change: A physical change is a temporary change in which no new substance is formed and the chemical composition of the original substance remains the same, even though its physical properties like colour, state, shape, size etc. might change.
(b) Chemical Change: A chemical change is permanent change in which new substances are formed whose chemical composition and physical and chemical properties are different from those of in original substance.

Question 2.
Classify the following as a physical or a chemical change.
(a) Drying of wet clothes
(b) Manufacture of salt from sea water
(c) Butter getting rancid
(d) Boiling of water
(e) Burning of paper
(f) Melting of wax
(g) Burning of coal
(h) Formation of clouds
(i) Making of a sugar solution
(j) Glowing of an electric bulb
(k) Curdling of milk
Answer:
Physical change
(a) Drying of wet clothes
(b) Manufacture of salt from sea water
(d) Boiling of water
(f) Melting of wax
(h) Formation of clouds
(i) Making of a sugar solution
(j) Glowing of an electric bulb.
Chemical change
(c) Butter getting rancid
(e) Burning of paper
(g) Burning of coal
(k) Curdling of milk

Question 3.
Fill in the blanks.
Answer:
(a) The process of a liquid changing into a solid is called freezing.
(b) A change, which alters the composition of a substances, is known as a chemical change.
(c) There is no change in the composition of the substance during a physical change.
(d) The reaction in which energy is evolved is called exothermic reaction.

Question 4.
Given reason:
(a) Freezing of water to ice and evaporation of water are physical changes.
(b) Burning of a candle is both a physical and chemical change.
(e) Burning of paper is a chemical change.
(d) Cutting of a cloth piece is a physical change, though it cannot be reversed.
Answer:
(a) Freezing of water to ice and evaporation of water are physical change because water can be brought back to its original (liquid) form by

  1. We can heat the ice to bring it back to water.
  2. We can cool down the vapours to bring it back to water.

(b) When a candle is lighted, some of the solid wax first melts and turns into liquid, then it turns into vapours to produce a flame. New substances CO2 and H2O vapours are formed alongwith the evolution of light and heat energy. This shows a chemical change. When some of the molten wax drops to the floor, it again solidifies. Which shows a physical change. Thus the melting of candle wax is a physical change and the production of CO2 and H2O represents chemical change.

(c) When a piece of paper is burnt a new substance ash is produced. Even when the burning is stopped, the ash cannot be changed back into paper. This shows that the formation of the ash from paper is a permanent and irreversible change.

(d) Because it does not change chemical composition of cloth and the change is only in the state, size, shape, colour, texture or the smell of some or all of the substances that undergo physical change.

Question 5.
Give four difference between physical and chemical changes.
Answer:
The differences are Physical and Chemical Changes:
Physical change

  1. In a physical change no new substance is formed and the chemical composition of substance remains same. There are changes only in physical properties and state.
  2. Temporaiy change which can be reversed by simple physical methods.
  3. Weight of original substance doesn’t change
  4. Energy like heat, light etc. may or may not be absorbed or released

Chemical change

  1. In a chemical change new substance with entirely different chemical composition and properties is formed.
  2. Permanent change and irreversible
  3. Weight of original substances may increase or decrease
  4. Energy like heat, light etc. are given out or absorbed.

Selina Concise Chemistry Class 8 ICSE Solutions – Chemical Reactions

Selina Concise Chemistry Class 8 ICSE Solutions – Chemical Reactions

ICSE Solutions  Selina ICSE Solutions  ML Aggarwal Solutions

ICSESolutions.com provides step by step solutions for Selina Concise ICSE Solutions for Class 8 Chemistry Chapter 6 Chemical Reactions. You can download the Selina Concise Chemistry ICSE Solutions for Class 8 with Free PDF download option. Selina Publishers Concise Chemistry for Class 8 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

Selina Class 8 Chemistry ICSE SolutionsPhysicsBiologyMathsGeographyHistory & Civics

Selina Concise ICSE Solutions for Class 8 Chemistry Chapter 6 Chemical Reactions

Exercise – I

Question 1.
(a) Define a chemical reaction.
(b) What happens during a chemical reaction?
(c) What do you understand by a chemical bond?
Answer:
(a) Any chemical change in a matter which involves transformation into one or more substances with entirely different properties is called a chemical reaction.
(b) A chemical reaction involves breaking of chemical bonds between the atoms or groups of atoms of reacting substances and rearrangement of atoms making new bonds to form new substances.
Selina Concise Chemistry Class 8 ICSE Solutions - Chemical Reactions 1
(c) A chemical bond is the attractive force that holds the atoms of a molecule together, in a compound.

Question 2.
Give one example each of which illustrates the following characteristics of a chemical reaction:
(a) evolution of a gas
(b) change of colour
(c) change in state
Answer:
(a) When Zinc reacts with dil. sulphuric acid. Hydrogen gas is evolved, with an effervescence
Selina Concise Chemistry Class 8 ICSE Solutions - Chemical Reactions 2

(b) When blue coloured copper sulphate reacts with hydrogen sulphide gas, a black coloured substance copper sulphide is formed.
Selina Concise Chemistry Class 8 ICSE Solutions - Chemical Reactions 3

(c) The reaction between hydrogen sulphide and chlorine (both gases) produces sulphur (solid) and hydrogen chloride (gas).
Selina Concise Chemistry Class 8 ICSE Solutions - Chemical Reactions 4

Question 3.
How do the following help in bringing about a chemical change?
(a) pressure (b) light
(c) catalyst (d) heat.
Answer:
(a) Some chemical reactions take place when reactants are subjected to high pressure.
e.g: Nitrogen and hydrogen when subjected to high pressure produce ammonia gas.
Selina Concise Chemistry Class 8 ICSE Solutions - Chemical Reactions 5

(b) Some chemical reactions can take place in the presence of light. Ex. Photosynthesis.
Selina Concise Chemistry Class 8 ICSE Solutions - Chemical Reactions 6

(c) A catalyst can either increases or decreases the rate of a chemical reaction and some chemical reactions need a catalyst to change the rate of the reaction, in case it is too slow or too fast.

  1. Positive catalyst: When a catalyst increases the rate of reaction finely divided iron is used as a positive catalyst in the manufacturing of ammonia from hydrogen and nitrogen.
    Selina Concise Chemistry Class 8 ICSE Solutions - Chemical Reactions 7
  2. Negative Catalyst: When a catalyst decreases the rate of reaction.
    Ex. Phosphoric acid act as a negative catalyst to decrease the rate of the decomposition of hydrogen peroxide.

(d) Some chemical reactions take place only in the presence of heat.
e.g. When lead nitrate is heated, it breaks into lead monoxide, nitrogen dioxide, and oxygen.
Selina Concise Chemistry Class 8 ICSE Solutions - Chemical Reactions 8

Question 4.
(a) Define catalyst.
(b) What are (i) positive catalysts and (ii) negative catalysts? Support your answer with one example for each of them.
(c) Name three biochemical catalysts found in the human body.
Answer:
(a) Catalyst: A catalyst is a substance that either increases or decreases the rate of a chemical reaction without itself undergoing any chemical change during the reaction.

(b) (i) Positive catalyst: When a catalyst increases the rate of chemical reaction, it is called a positive catalyst.
e.g. when potassium chlorate heated to 700°C decomposes to evolve oxygen gas, when MnO2 has added the decomposition takes place at 300°C
Selina Concise Chemistry Class 8 ICSE Solutions - Chemical Reactions 9
(ii) Negative catalyst: When a catalyst decreases the rate of chemical reaction it is called a negative catalyst.
Example. Phosphoric acid acts as a negative catalyst to decrease the rate of the decomposition of hydrogen peroxide. Alcohol too acts as a negative catalyst in certain chemical reactions.

(c) Biochemical catalysts found in the human body:

  1. Pepsin
  2. Trypsin
  3. lipase.

Question 5.
What do you observe when
(a) dilute sulphuric acid is added to granulated zinc?
(b) a few pieces of iron are dropped in a blue solution of copper sulphate?
(c) silver nitrate is added to a solution of sodium chloride?
(d) ferrous sulphate solution is added to an aqueous solution of sodium hydroxide.
(e) solid lead nitrate is heated?
(f) when dilute sulphuric acid is added to barium chloride solution?
Answer:
(a) When Zinc reacts with dilute sulphuric acid, hydrogen gas is evolved with effervescence.
Zn + dil. H2SO4 → Zn SO4 + H2.

(b) When a few pieces of iron are dropped into a blue coloured copper sulphate solution, the blue colour of the solution fades and eventually turns green.

(c) When a solution of silver nitrate is added to a solution of sodium chloride, white insoluble ppt. of silver chloride is formed.
AgNO3 (aq) + NaCl (aq) → AgCl (ppt) + NaNO3 (aq)

(d) When ferrous sulphate solution is added to sodium hydroxide solution, a dirty green ppt. of ferrous hydroxide is formed.
FeSO4 (aq) + 2NaOH (aq) → Fe(OH)2 ↓ + Na2SO4(aq)

(e) When solid lead nitrate is heated, it decomposes to produce light yellow solid lead monoxide, reddish-brown nitrogen dioxide gas and colourless oxygen gas.
Selina Concise Chemistry Class 8 ICSE Solutions - Chemical Reactions 10

(f) When few drops of dilute sulphuric acid is added to barium chloride solution, a white precipitate of barium sulphate is formed.
Selina Concise Chemistry Class 8 ICSE Solutions - Chemical Reactions 11

Question 6.
Complete and balance the following chemical equations:
Selina Concise Chemistry Class 8 ICSE Solutions - Chemical Reactions 12
Answer:
Selina Concise Chemistry Class 8 ICSE Solutions - Chemical Reactions 13
Selina Concise Chemistry Class 8 ICSE Solutions - Chemical Reactions 14

Exercise – II

Question 1.
1. Fill in the blanks.
(a) A reaction in which two or more substances combine to form a single substance is called a combination reaction.
(b) A catalyst is a substance which changes the rate of a chemical reaction without undergoing a chemical change.
(c) The formation of gas bubbles in a liquid during a reaction is called effervescence
(d) The reaction between an acid and a base is called a neutralization reaction.
(e) Soluble bases are called alkalis.
(f) The chemical change involving iron and hydrochloric acid illustrates a displacement reaction.
(g) In the type of reaction called double decomposition reaction, ions two compounds exchange their positive and negative radicals ions respectively.
(h) A catalyst either increases or decreases the rate of a chemical change but itself remains unchanged at the end of the reaction.
(i) The chemical reaction between hydrogen and chlorine is a combination reaction
(j) When a piece of copper is added to silver nitrate solution, it turns blue in colour.

Question 2.
Classify the following reactions as a combination, decomposition, displacement, precipitation, and neutralization. Also, balance the equations.
Selina Concise Chemistry Class 8 ICSE Solutions - Chemical Reactions 15
Selina Concise Chemistry Class 8 ICSE Solutions - Chemical Reactions 16
Answer:
Selina Concise Chemistry Class 8 ICSE Solutions - Chemical Reactions 18

Question 3.
Define:
(a) precipitation (b) neutralization (c) catalyst
Answer:
(a) Precipitation: A chemical reaction in which two compounds in their aqueous state react to form an insoluble salt as one of the product.
Acid + Base → Salt + Water
Example.
Selina Concise Chemistry Class 8 ICSE Solutions - Chemical Reactions 19

(b) Neutralization: A chemical reaction in which a base or an alkali reacts, with an acid to produce a salt and water only.
Selina Concise Chemistry Class 8 ICSE Solutions - Chemical Reactions 20

(c) Catalyst: A catalyst is a substance that either increases or decreases the rate of a chemical reaction without itself undergoing any chemical change.
Selina Concise Chemistry Class 8 ICSE Solutions - Chemical Reactions 21
here iron act as a catalyst and increases the rate of a chemical reaction.

Question 4.
Explain the following types of chemical reactions giving two examples for each of them.
(a) combination reaction
(b) decomposition reaction
(c) displacement reaction
(d) double decomposition reaction
Answer:
(a) Combination reaction: A reaction in which two or more substances combine to form a single substance is called a combination reaction.
A + B → AB
e.g (i) When iron and sulphur are heated together, they combine to form iron sulphide.
Selina Concise Chemistry Class 8 ICSE Solutions - Chemical Reactions 22
(ii) When carbon bums in oxygen to form a gaseous compound called carbon dioxide.
Selina Concise Chemistry Class 8 ICSE Solutions - Chemical Reactions 23
(b) Decomposition reaction: A reaction in which a compound breaks up due to the application of heat into two or more simple substances is called a decomposition reaction.
Selina Concise Chemistry Class 8 ICSE Solutions - Chemical Reactions 24
e.g. (i) Mercuric oxide when heated, decomposes to form two elements mercury and oxygen
Selina Concise Chemistry Class 8 ICSE Solutions - Chemical Reactions 25
(ii) CaCO3 when heated decomposes to calcium oxide and carbon dioxide.
Selina Concise Chemistry Class 8 ICSE Solutions - Chemical Reactions 26

(c) Displacement reaction: A reaction in which a more active element displaces a less active element from a compound is called a displacement reaction.
AB + C → CB + A
e.g. (i) Zinc, displaces copper from copper sulphate solution.
Zn + CuSO4 (aq) → ZnSO4 (aq) + Cu
(ii) Iron piece when added to copper sulphate solution, copper is displaced.
Fe + CuSO4 → FeSO4 + Cu.

(d) Double decomposition reaction: A chemical reaction in which two compounds in their aqueous state exchange their ions to form new compounds is called a double decomposition reaction.
AB + CD → CB + AD
e.g. (i) AgNO3 + HCl  AgCl + HNO3(aq)
(ii) NaOH (aq) + HCl (aq)  NaCl (aq) + H2O.

Question 5.
Write the missing reactants and products and balance the equations.
Selina Concise Chemistry Class 8 ICSE Solutions - Chemical Reactions 27
Answer:
Selina Concise Chemistry Class 8 ICSE Solutions - Chemical Reactions 28

Question 6.
How will you obtain it?
(a) Magnesium oxide from magnesium.
(b) Silver chloride from silver nitrate.
(c) Nitrogen dioxide from lead nitrate.
(d) Zinc chloride from zinc.
(e) Ammonia from nitrogen.
Also, give balanced equations for the reactions
Answer:
(a) Magnesium when burnt in air (oxygen) Magnesium oxide is formed
Selina Concise Chemistry Class 8 ICSE Solutions - Chemical Reactions 29

(b) When silver nitrate solution reacts with sodium chloride, silver chloride is formed.
Selina Concise Chemistry Class 8 ICSE Solutions - Chemical Reactions 30

(c) Lead nitrate when heated nitrogen oxide is obtained
Selina Concise Chemistry Class 8 ICSE Solutions - Chemical Reactions 31

(d) Zinc when reacts with hydrochloric acid zinc chloride and hydrogen (g) is formed.
Zn + 2HCl → ZnCl2 + H2

(e) Nitrogen when reacts with hydrogen at 450°C and under 200 atm, ammonia is formed.
Selina Concise Chemistry Class 8 ICSE Solutions - Chemical Reactions 32

Question 7.
What do you observe when
(a) Iron nail is kept in copper sulphate solution for some time.
(b) Phenolphthalein is added to sodium hydroxide solution.
(c) Blue litmus paper is dipped in dilute hydrochloric acid.
(d) Lead nitrate is heated.
(e) Magnesium ribbon is burnt in oxygen.
(f) Ammonia is brought in contact with hydrogen chloride. gas.
Answer:
(a) A brown layer of copper gets deposited on an iron nail. This is due to a chemical reaction.
Fe (s) + CuSO4 (aq) → FeSO4 (aq) + Cu (s)
(b) Solution turns pink.
(c) Blue litmus turns red in an acid solution.
(d) The pale yellow solid is lead monoxide, the reddish-brown gas is nitrogen dioxide and the colourless gas is oxygen.
Selina Concise Chemistry Class 8 ICSE Solutions - Chemical Reactions 33
(e) Magnesium ribbon bums with a dazzling white light and produces a white powder which is magnesium oxide.
The reaction can be represented as
2Mg + O2 → 2MgO (white powder)
(f) Ammonia and hydrogen chloride, both compounds, combine to form a compound, ammonium chloride.
Selina Concise Chemistry Class 8 ICSE Solutions - Chemical Reactions 34

Question 8.
Give reason:
(a) A person suffering from acidity is advised to take an antacid.
(b) Acidic soil is treated with quick lime.
(c) Wasp sting is treated with vinegar.
Answer:
(a) An antacid neutralizes stomach acidity.
(b) If the soil is acidic it can be treated with a base like quick lime, to make it neutral.
(c) Wasp stings are alkaline and can be neutralized by vinegar which is a weak acid.

Question 9.
What is meant by the metal reactivity series? State its importance, (any two points).
Answer:
A list in which the metals are arranged in the decreasing order of their chemical reactivity is called the metal reactivity series.
Selina Concise Chemistry Class 8 ICSE Solutions - Chemical Reactions 35
Special features of the activity series:

  1. The ease with which a metal in solution loses an electron(s) and forms a positive ion decreases down the series, i.e. from potassium to gold.
  2. Hydrogen is included in the activity series because, as metals do, it too loses an electron and becomes positively charged (H+) in most chemical reactions.
  3. The series facilitates the comparative study of metals in terms of the degree of their reactivity.
  4. The compounds of the metals (oxides, carbonates, nitrates and hydroxides) too can be easily compared.

Question 10.
What are oxides? Give two examples of each of the following oxides.
(a) Basic oxide (b) Acidic oxide
(c) Amphoteric oxide (d) Neutral oxide
Answer:
An oxide is a compound that essentially contains oxygen in its molecule, chemically combined with a metal or a non-metal.
Selina Concise Chemistry Class 8 ICSE Solutions - Chemical Reactions 36

Question 11.
Define exothermic and endothermic reactions. Give two examples of each.
Answer:
Exothermic reactions: The chemical reaction in which heat is given out is called exothermic reactions. It causes rise in temperature. .
e.g. (i) When carbon bums in oxygen to form carbon dioxide, a lot of heat is produced.
C + O2 → CO2 + heat.
When water is added to quicklime a lot of heat is produced which boils the water.
CaO + H2O → Ca (OH)2 + Heat.

Endothermic reaction: A chemical reaction in which heat is absorbed is called endothermic reaction. It causes fall in temperature.
e.g. (i) When nitrogen and oxygen together are heated to a temperature of about 3000°C, nitric oxide gas is formed.
N2 + O2 + heat → 2NO (g)
(ii) Decomposition of calcium carbonate into carbon dioxide and calcium oxide when heated to a 1000°C.
CaCO3 + Heat → CaO (s) + CO2 (g)

Question 12.
State the effect of:
(a) an endothermic reaction
(b) an exothermic reaction on the surroundings.
Answer:
(a) Carbon dioxide present in the atmosphere is trapped by infrared radiations, gives rise to temperature which is exothermic reaction.
(b) The melting of glaciers by global warming.

Question 13.
What do you observe when
(a) an acid is added to a basic solution.
(b) ammonium chloride is dissolved in water.
Answer:
(a) A chemical reaction in which a base or an alkali reacts with an acid to produce a salt and water.
Acid + Base → Salt + Water
(b) Dissolution of ammonium chloride in water is an endothemic reaction in which heat energy is absorbed.

Selina Concise Chemistry Class 8 ICSE Solutions – Matter

Selina Concise Chemistry Class 8 ICSE Solutions – Matter

ICSE Solutions  Selina ICSE Solutions  ML Aggarwal Solutions

ICSESolutions.com provides step by step solutions for Selina Concise ICSE Solutions for Class 8 Chemistry Chapter 1 Matter. You can download the Selina Concise Chemistry ICSE Solutions for Class 8 with Free PDF download option. Selina Publishers Concise Chemistry for Class 8 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

Selina Class 8 Chemistry ICSE SolutionsPhysicsBiologyMathsGeographyHistory & Civics

Selina Concise ICSE Solutions for Class 8 Chemistry Chapter 1 Matter

Exercise

Question 1.
Define:
(a) matter
(b) intermolecular force of attraction.
Answer:
(a) Matter is anything which has mass, occupies space and can be percieved by our senses.
Example: Air, Book.
(b) The molecules of matter are always in motion and attract each other with a force called intermolecular force of attraction due to which they are held together.

Question 2.
What are the three states of matter ? Define each of them with two examples.
Answer:
The three states of matter are:
solids, liquids and gases

  • Solids — A solid has a definite shape and definite volume.
    Example – wood, stone, iron, ice etc.
  • Liquid — A liquid has a definite volume but not definite shape.
    Example — water, juice, milk, oil, etc.
  • Gases — A gas neither has definite shape nor a definite volume.
    Example – air, hydrogen, oxygen, watervapour etc.

Question 3.
Define interconversion of states of matter. What are the two factors responsible for the change of states of matter?
Answer:
The process by which matter changes from one state to another and back to original state, without any change in its chemical composition is called interconversion state of matter.
Two factors responsible for change of state of matter are: change in
(i) Temperature (ii) Pressure

Question 4.
State the main postulates of kinetic theory of matter.
Answer:
The main postulates of the theory are:

  1. Matter is composed of very small particles called atoms and molecules.
  2. The constituent particles of a kind of matter are identical in all respects.
  3. These particles have space or gaps between them which is known as interparticular or intermolecular space.
  4. There exists a force of attraction between the particles of matter which holds them together. This force of attraction is known as interparticular or intermolecular force of attraction.
  5. Particles of matter are always in a state of random motion and possess kinetic energy, which increases with increase in temperature and vice-versa.

Question 5.
What happens to water if
(a) it is kept in a deep freezer
(b) it is heated
Explain the phenomenon of change of state of water.
Answer:
(a) When water is kept in a deep freezer, it gets cooled and change into ice at 0°C ice.
Selina Concise Chemistry Class 8 ICSE Solutions - Matter 1
(b) Water on heating changes into steam at 100°C
Selina Concise Chemistry Class 8 ICSE Solutions - Matter 2

Phenomenon of change of state of water:
Water is a liquid under ordinary conditions but, when it is kept in a deep freezer, it changes into ice at 0°C and when ice is kept at room temperature again changes back into liquid water.
Similarly, water on heating change into steam at 100°C, which on cooling changes back into liquid water. But there is no change in the chemical composition of water. When its state changes from liquid to solid or liquid to gaseous state.
Selina Concise Chemistry Class 8 ICSE Solutions - Matter 3

Question 6.
(a) State the law of conversation of mass.
(b) What do you observe when barium chloride solution is mixed with sodium sulphate solution?
Answer:
(a) “Matter can neither be created nor be destroyed in a chemical reaction”. However, it may change from one form to another in the process.
It can also be stated as, “In a chemical reaction, the total mass of the reactants is equal to the total mass of the products”.

(b)
Selina Concise Chemistry Class 8 ICSE Solutions - Matter 4
We will observe that a white insoluble solid (precipitate) of barium sulphate is formed along with a solution of sodium chloride. Wait for ten minutes to complete the reaction and the solid formed to settle down.
Weigh the content again and note the reading.
We will observe that,
total mass of the apparatus + reactants = total mass of apparatus + products
Hence the law of conservation of mass is verified.

Question 7.
Give reasons:
(a) A gas can fill the whole vessel in which it is enclosed.
(b) Solids cannot be compressed.
(c) Liquids can flow.
(d) When magnesium is burnt in air, there is an increase in mass after the reaction.
Answer:
(a) Because, in gases, the molecules are free to move.
They are not stuck to each other and the intermolecular force of attraction is least in the gases. So the gas almost filled the whole vessel in which it is enclosed.

(b) In solids, particles are closely packed. There is a strong force of attraction and the intermolecular space is almost zero. Therefore the molecules are not free to move, which makes them hard and rigid. So solids can not be compressed.

(c) In liquids intermolecular force is weaker because the particles are not closely packed and hence there is large intermolecular space. So molecules in a liquids can move randomely and hence liquids can flow easily.

(d) When magnesium ribbon is burnt in air, a white solid, magnesium oxide is formed. The mass of magnesium oxide is more than the mass of magnesium. This is because mass of oxygen used is not taken. If that is considered, the total mass of the reactants and the products is found to be almost equal.
Selina Concise Chemistry Class 8 ICSE Solutions - Matter 5

Question 8.
Fill in the blanks:

(a) The change of a solid into a liquid is called melting or fusion.
(b) The process in which a solid directly changes into a gas is called sublimation.
(c) The change of water vapour into water is called condensation.
(d) The temperature at which a liquid starts changing into its vapour state is evaporation or vaporisation.

Question 9.
Give two examples for each of the following:
(a) The substances which sublime.
(b) The substances which do not change their state on heating.
Answer:
(a) Camphor, iodine, naphthalene, ammonium chloride, dry ice (solid carbon dioxide), etc.
(b) Gases do not change their state on heating.
Example: O2.

Question 10.
Define:
(a) Diffusion.
(b) Brownian motion.
Answer:
(a) Diffusion: The intermixing of two or more substances due to the motion of their particles in order to get a uniform mixture is called ‘diffusion’.
(b) Brownian motion: The haphazard, random motion of suspended particles on the surface of a liquid or in air is called ‘Brownian motion’.

Question 11.
When sodium chloride is added to a definite volume of water and stirred well, a solution is formed, but there is no increase in the level of water. Why?
Answer:
This is because there is some space between the particles of water in which the salt particles get accomodated when dissolved.

Question 12.
What do you observe when a gas jar which appears empty is inverted over a gas jar containing Bromine vapours? Name the phenomenon.
Answer:
When a gas jar full of bromine vapours (reddish brown) is inverted over a gas jar containing air over it. It is observed that after sometime, the reddish brown vapours of bromine also spread out into the upper jar. This mixing is called diffusion. The rate of diffusion is the fastest in gases and the slowest in solids. It increases with an increase in temperature.

Question 13.
Why can a piece of chalk be broken easily into smaller pieces while a coal piece cannot be broken easily?
Answer:
The particles of matter have force acting between them. This force keeps the particles together. The strength of this force of attraction is lesser in chalk, hence it could be broken easily into smaller pieces.
But the strength of inter-molecular force of attraction is very strong in coal, therefore it is not possible to break them into small pieces.

Selina Concise Chemistry Class 8 ICSE Solutions – Elements, Compounds and Mixtures

Selina Concise Chemistry Class 8 ICSE Solutions – Elements, Compounds and Mixtures

ICSE Solutions  Selina ICSE Solutions  ML Aggarwal Solutions

ICSESolutions.com provides step by step solutions for Selina Concise ICSE Solutions for Class 8 Chemistry Chapter 3 Elements, Compounds and Mixtures. You can download the Selina Concise Chemistry ICSE Solutions for Class 8 with Free PDF download option. Selina Publishers Concise Chemistry for Class 8 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

Selina Class 8 Chemistry ICSE SolutionsPhysicsBiologyMathsGeographyHistory & Civics

Selina Concise ICSE Solutions for Class 8 Chemistry Chapter 3 Elements, Compounds and Mixtures

Exercise 3(A)

Question 1.
Define: (a) Elements (b) Compounds
Answer:
(a) Elements: Element is a substance which cannot be broken further into simpler substances and has a definite set of properties. Elements are made up of only one kind of atoms.
(b) Compounds: Compounds are pure substances composed of two or more elements in definite proportion by mass and has properties, entirely different from those of its constituents elements.
Compound, are made up of different types of atoms combined chemically.

Question 2.
Give two examples for each of the following:
(a) Metals (b) Non-metals
(c) Metalloids (d) Inert gases
Answer:
(a) Metals: Iron, silver, gold.
(b) Non-metals: Carbon, sulphur, oxygen.
(c) Metalloids: Antimony, silicon, boron.
(d) Inert gases: Helium, argon, neon.

Question 3.
Differentiate between:
(a) Pure and impure substances
(b) Homogenous and heterogenous substances
Answer:
(a) Pure substances —

  1. Pure substances have definite composition and definite physical and chemical properties.
  2. They are all homogeneous i.e. their composition is uniform throughout the bulk.
  3. Examples: Elements and compounds.

Impure substances —

  1. Impure substances are made up of two or more pure substances mixed together in any proportion.
  2. They may be homogeneous or hetergeneous i.e. their composition is not uniform throughout the bulk.
  3. They are all mixtures.
    Examples: air, sea water, petroleum, a solution of sugar in water are all impure substances.

(b) Homogeneous mixture — is a mixture where the components that make up the mixture are uniformly distributed throughout the mixture.
Example — air, sugar water, rain water.
Heterogeneous mixture — is a mixture, where the components of the mixture are not uniform or have localized regios with different properties.
Example—Cereal in milk, vegetable soup.

Question 4.
Write the chemical name of the following and also give their molecular formulae:
(a) Baking soda (b) Vinegar
(c) Marble (d) Sand
Answer:
(a) Sodium bicarbonate (Baking soda) — NaHCO3
(b) Acetic acid (Vinegar) — CH3COOH
(c) Calcium carbonate (Marble) — CaCO3
(d) Silicon dioxide (Sand) — SiO2

Question 5.
Name:
(a) a soft metal
(b) a metal which is brittle
(c) a non-metal which is lustrous
(d) a liquid metal
(e) a metal which is a poor conductor of electricity.
(f) a non-metal which is a good conductor of electricity.
(g) a liquid non-metal
(h) the hardest naturally occurring substance
(i) an inert gas
Answer:
(a) Gold
(b) Zinc
(c) Iodine
(d) Mercury
(e) Tungsten
(f) Graphite
(g) Bromine
(h) Diamond
(i) Neon, helium

Question 6.
How is sodium chloride different from its constituent elements ?
Answer:
The properties of sodium chloride are completely different from those of sodium and chlorine. Sodium is a soft, highly reactive metal. Chlorine is a poisonous non-metallic gas while sodium chloride is a very useful non poisonous compound which is added to our food to get minerals and also to add taste to it.

Question 7.
Why is iron sulphide a compound ?
Answer:
Iron sulphide is a compound which can be broken into the elements iron and sulphur they both have different properties. The properties of compound are entirely different from there of its constituents elements.

Exercise 3(B)

Question 1.
Classify the following substances into compounds and mixtures:
Answer:
Carbon dioxide, air, water, milk, common, salt, blood, fruit juice, iron sulphide.
Carbon dioxide — (Compound)
air — (Mixture)
water — (Compound)
milk — (Mixture)
common salt — (Compound)
blood — (Mixture)
fruit juice — (Mixture)
iron sulphide — (Compound)

Question 2.
Give one example for each of the following types of mixtures
(a) solid-solid homogenous mixture
(b) solid-liquid heterogenous mixture
(c) misicible liquids
(d) liquid-gas homogenous mixture
Answer:
(a) Solid-solid homogenous mixture — Alloys of metals e.g. brass, bronze stainless steel etc.
(b) Solid-liquid heterogenous mixture — Sand and water, mud and water, sugar and oil.
(c) Misicible liquids — water and ethanol.
(d) Liquid-gas homogenous mixture — Air

Question 3.
Suggest a suitable technique to separate the constituents of the following mixtures. Also give the reason for selecting the particular method.
(a) Salt from sea water
(b) Ammonium chloride from sand
(c) Chalk powder from water
(d) Iron from sulphur
(e) Water and alcohol
(f) Sodium chloride and potassium nitrate
(g) Calcium carbonate and sodium chloride
Answer:

(a) The technique used to separate the salt from seawater is Evaporation.
Reason – Because this method is used to separate the components of the homogeneous solid-liquid mixture. In this method, sea water is collected in a shallow bed and allowed to evaporate in the sun. When all the water is evaporated, salt is left behind. By this method, we only get solid and liquid is evaporated in its vapour form.

(b) Technique used to separate Ammonium chloride from sand is sublimation.
Because this method is used for solid mixtures in which one of the components can sublime on heating. In this method, Ammonium chloride changes into vapours on heating and salt is left behind.

(c) Technique used to separate chalk powder from water is filtration.
Reason – Because this process is used to separate the components of a heterogeneous solid-liquid mixture in which solids are lights and insoluble in liquids. Substances used as filters are sand filter paper at C. These filters allows the liquid to pass through them, but not solids.

(d) Technique to separate iron from sulpher is magnetic separation.
Because, this method is used when one of the component of mixture is Iron. Iron gets attracted towards the magnet and hence get separated.

(e) Technique used to separate water and Alcohol is Fractional Distillation.
Because in this method, the vapours of water is left behind in the original vessel as the alcohol boils at lower temperature than water. Thus these two liquids can be separated.

(f) Technique used is Fractional-crystallisation.
Because: This method is used when solubility of solid components of mixture and different in the same solvent. Here, sodium chloride and potassium nitrate. Both are soluble in water but solubility of potassium nitrate is more.

(g) Technique used is Solvent Extraction Method: Because, by this method, salts get dissolve in water while calcium carbonate being insoluble in water settles down in the container. And hence get separated about.

Question 4.
(a) Define mixture.
(b) Why is it necessary to separate the constituents of a mixture.
(c) State four differences between compounds and mixtures.
Answer:
(a) “Mixtures can be defined as. a kind of matter which is formed by mixing two or more pure substances (elements and compounds) in any proportion, such that they do not undergo any chemical change and retain their individual properties. Therefore they are impure substances.

(b) Because: The mixtures contain unwanted substances which may be harmful and may degrade the properties of mixtures. So we, need to separated them and extract useful substances.
This is necessary because
(i) It removes unwanted and harmful substances
(ii) to obtain pure and useful substances them.
Example: Sea water is rich in common salt which is an important ingredient of our food to add taste and nutrients. But sea water, cannot be directly used to get the salt.
Hence, it is necessary to separate both.

(c) Compound

  1. A compound is formed from its constituent elements as a result of chemical reaction.
  2. A compound is always homogeneous in nature.
  3. In a compound the elements are present in a fixed ratio by weight.
  4. The components of a compound can’t be separated by physical methods but can be separated by chemical methods only.
  5. The properties of a compound are different from those of its elements.
  6. The formation of a compound from its elements is accompanied by energy changes.

Mixture

  1. A mixture is obtained form its (elements, compounds) components as a result of physical change.
  2. The mixtures can be homogeneous or heterogeneous.
  3. In a mixture the components can be present in any ratio.
  4. The components of a mixture can be separated by physical methods only.
  5. The properties of a mixture lie between those of-its components.
  6. The formation of a mixture from its constituents is not accompanied by energy changes.

Question 5.
(a) What is chromatography ? For which type of mixture is it used ?
(b) What are the advantages of chromatography.
Answer:
(a) This is one of the latest techniques to separate the coloured components of a mixture when all the components are very similar in their properties. Example: Components of ink are separated by this method. Ink is a mixture of different dyes, which are separated by chromatography because some of the dyes are less soluble and some are more soluble in a solvent.

(b)

  1. A very small quantity of the substance can be separated.
  2. Components with very similar physical and chemical properties can be separated.
  3. It identifies the different constitutes of a mixture.
  4. It also helps in quantitive estimation of components of a mixture.

6. Choose the most appropriate answer from the options given below:

(a) a mixture of sand and ammonium chloride can be separated by

  1. filtration
  2. distillation
  3. sublimation
  4. crystallisation

(b) A pair of metalloids are

  1. Na and Mg
  2. B and Si
  3. C and P
  4. HeandAr

(c) Which of the following property is not shown by compounds?

  1. They are heterogeneous.
  2. They are homogeneous.
  3. They have definite molecular formulae.
  4. They have fixed melting and boiling points.

(d) A solvent of Iodine is

  1. Water
  2. Kerosene oil
  3. Alcohol
  4. Petrol

(e) Which of the gas is highly soluble in water ?

  1. Ammonia
  2. Nitrogen
  3. Carbon monoxide
  4. Oxygen

Selina Concise Chemistry Class 8 ICSE Solutions – Carbon and Its Compounds

Selina Concise Chemistry Class 8 ICSE Solutions – Carbon and Its Compounds

ICSE Solutions  Selina ICSE Solutions  ML Aggarwal Solutions

ICSESolutions.com provides step by step solutions for Selina Concise ICSE Solutions for Class 8 Chemistry Chapter 9 Carbon and Its Compounds. You can download the Selina Concise Chemistry ICSE Solutions for Class 8 with Free PDF download option. Selina Publishers Concise Chemistry for Class 8 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

Selina Class 8 Chemistry ICSE SolutionsPhysicsBiologyMathsGeographyHistory & Civics

Selina Concise ICSE Solutions for Class 8 Chemistry Chapter 9 Carbon and Its Compounds

Points to Remember:

  1. Carbon occurs in the earth’s crust in the free as well as in the combined state.
  2. In the free state, it occurs as coal, diamond and graphite.
  3. In the combined state, carbon occurs in atmosphere (CO2) natural gas, food nutrients and carbonates.
  4. Diamond is the hardest naturally occuring substance known.
  5. Fullerenes are discovered only recently.

Exercise – I

Question 1.
Fill in the blanks.
(a) Carbon is present in both living and non-living things.
(b) The tendency of an element to exist in two or more forms but in the same physical state is called Allotropy.
(c) Crystalline and non-crystalline are the two major crystalline allotropes of carbon.
(d) Diamond is the hardest substance that occurs naturally.
(e) The name ‘carbon’ is derived from the Latin word carbo.

Question 2.
Choose the correct alternative.

(a) In a combined state, carbon occurs as
(i) coal
(ii) diamond
(iii) graphite
(iv) petroleum

(b) A crystalline form of carbon is
(i) lampblack
(ii) gas carbon
(iii) sugar
(iv) fullerene

(c) Graphite is not found in
(i) Bihar
(ii) Maharashtra
(iii) Orissa
(iv) Rajasthan

(d) Diamond is used for
(i) making the electrodes of electric furnaces.
(ii) making crucible for melting metals.
(iii) cutting and drilling rocks and glass.
(iv) making carbon brushes for electric motors.

(e) Carbon forms innumerable compounds because
(i) it has four electrons in its outermost shell.
(ii) it behaves as metal as well as non-metal.
(iii) carbon atoms can form long chains.
(iv) it combines with other elements to form covalent compounds.

Question 3.
Write ‘true’ or ‘false’ against the following statements.

(a) Carbon constitutes 0.03% of the earth’s crust. – True
(b) Graphite is the purest form of carbon. – False
(c) Coloured diamonds are costlier than colourless and transparent diamonds. – False
(d) Graphite has layers of hexagonal carbon bondings. – True
(e) Diamond is insoluble in all solvents. – True.

Question 4.
Define the following terms:

(a) Allotropy (b) Carat
(c) Crystal (d) Catenation
Answer:
(a) Allotropy: Allotropy is defined as the phenomenon due to which an element exists in two or more forms in the same physical state with identical chemical properties but with different physical properties.

(b) Carat – The weight of diamond is expressed in carats [ 1 carat = 0.2 g]

(c) Crystal – A crystal is a homogeneous solid in which particles (atoms, molecules, or ions) are arranged in the definite pattern due to which they have a definite geometrical shape with plane surfaces e.g. sugar and sodium chloride.

(d) Catenation – A large number of organic compounds is due to the ability of carbon atoms to form long chains with other carbon atoms through the sharing of electrons. This unique property of carbon is known as catenation.
Selina Concise Chemistry Class 8 ICSE Solutions - Water 6

Question 5.
State the terms:

(a) Substances whose atoms or molecules are arranged in a definite pattern. – Crystals.
(b) Different forms of an element found in the same physical state. – Allotropy.
(c) The property by which atoms of an element link together to form long chain or ring compounds. – Catenation

Question 6.
Name the following:

(a) The hardest naturally occurring substance. – Diamond.
(b) A greyish black non-metal that is a good conductor of electricity. – Graphite.
(c) The third crystalline form of carbon. – Fullerenes.

Question 7.
Answer the following questions:

(a) Why is graphite a good conductor of electricity but not diamond?
(b) Why is diamond very hard?
(c) What are fullerenes? Name the most common fullerenes.
(d) What impurity is present in black diamond?
(e) Explain the softness of graphite with reference to its structure.
Answer:
(a) In a graphite molecule, one valence electron of each carbon atom remains free, Thus making graphite a good conductor of electricity. Whereas in diamond, they have no free mobile electron. Thats why diamond are bad conductor electricity.

(b) A diamond is a giant molecule. The number of valence electrons in carbon atom is four. As such each carbon atom is linked with four neighboring carbon atoms. Thus forming a rigid tetrahedral structure. It is the strong bonding’that makes diamond the hardest substance.

(c) Fullerenes: Fullerenes are the third crystalline form of carbon.
Though they were discovered only recently. They have.been found to exist in interstellar dust as well as in the geological formations of the earth.
Common fullerenes are C – 32, C – 50, C – 70 and C – 76

(d) Black diamonds have copper oxide present in them as impurity.

(e) In a graphite molecule of each carbon atoms is linked with three neighboring carbon atoms. Thus forming a hexagonal arrangement of atoms. These hexagonal grouping of carbon atoms are arranged as layers or sheets piled one the top of other. The layers are held together by weak forces such that they can slide over one another. That is why graphite is soft.

Question 8.
Give two uses of (a) graphite (b) diamond.
Answer:

(a) Uses of graphite:

  1. For making the electrodes of electric furnaces.
  2. For making crucibles for melting metals due to its high melting points.

(b) Uses of Diamond:

  1. Diamond is used in jewellery as a gem
  2. It is used for cutting and drilling rocks, glass,

Question 9.
Write three differences between graphite and diamond.
Answer:
Difference between diamond and graphite.

Diamond

  1. Pure diamond is colourless and transparent.
  2. It is the hardest naturally occurring substance.
  3. It has high density i.e. 3.5 g/cm3
  4. It is bad conduct of electricity.
  5. It bums in air at 900°C to form carbon dioxide.

Graphite

  1. Graphite is greyish black opaque and shiny.
  2. It is soft and greasy to touch.
  3. It has low density i.e. 2.39 g / cm3
  4. It is good conductor of electricity.
  5. It bums in air at 700° C to form carbon dioxide.

Exercise – II

Question 1.
Fill in the blanks:

(a) Charcoal is formed when charcoal is burnt in a limited supply of air.
(b) Coal is a amorphous form of carbon.
(c) Peat is the most inferior form of coal.
(d) Wood charcoal is a bad conductor of heat and electricity.
(e) lampblack is used in making black shoe polish.

Question 2.
Choose the correct alternative

(a) Anthracite is
(i) an inferior type of coal
(ii) a superior type of coal
(iii) a cheapest form of coal
(iv) none of above

(b) Destructive distillation of coal yields
(i) coal tar
(ii) coal gas
(iii) coke
(iv) all of the above

(c) Lamp black is
(i) an amorphous form of carbon
(ii) a crystalline form of carbon
(iii) a pure form of carbon
(iv) a cluster of carbon atoms

(d) The process by which decayed plants slowly convert into coal is called.
(i) petrification
(ii) carbonisation
(ii) carbonification
(iv) fermentation

(e) The purest form of the amorphous carbon is
(i) wood charcoal
(ii) sugar charcoal
(iii) bone charcoal
(iv) lampblack

Question 3.
Write ‘true’ or ‘false’ against the following statements:

(a) Charcoal is a good adsorbent. True
(b) Coke is obtained by destructive distillation of sugar. False
(c) Activated charcoal is a good conductor of electricity. False
(d) Wood charcoal is an important constituent of gun powder. True
(e) Coal gas is used in the preparation of artificial ferilizers. False.

Question 4.
Define the following:

(a) Carbonization
(b) Adsorption
(c) Bone black
Answer: 
(a) Carbonization: The process of the slow conversion of vegetable matter into carbon-rich substances is called carbonization.
(b) Adsorption: Adsorption is the property due to which a substance absorbs gases, liquids and solids on its surface.
(c) Bone black: The Carbon content of bone charcoal is separated by treating the latter with hydrchloride acid, which dissolves the calcium phosphate. Carbon is then filtered out of the solution and in this form it is called bone black.

Question 5.
Name the following:

(a) Substances whose atoms or molecules are not arranged in a geometrical pattern. – Amorphous
(b) The best variety of coal. – Bituminous
(c) The purest form of amorphous carbon. – Anthracite
(d) An amorphous form of carbon that contains about 98% carbon. – Anthracite
(e) Mixture of carbon monoxide and hydrogen. – Water gas.

Question 7.
Answer the following questions:

(a) What is destructive distillation? What are the products formed due to the destructive distillation of coal?
(b) Why is wood charcoal used in water filters and gas masks?
(c) How is wood charcoal made locally? What other substances are formed in the process.
(d) How many carbon atoms are there in Buckminster fullerenes?
Answer: 
(a) Destructive Distillation: When a substances is heated in the absence of air. The process is called destructive distillation.
Products formed are: Coke, Coal tar, Coal gas and ammonia solution

(b) Due to its high adsorbing capacity, wood charcoal is used as gas masks to adsorb harmful gases. Wood charcoal is porous, that is why it is used to filter water.

(c) Wood charcoal is prepared when wood is heated in a limited supply of air. Locally wood charcoal is prepared by piling logs of wood one above the other with a gap in the centre of the pile. The pile is covered with wet clay to prevent the entry of air. A few holes are left at the bottom of the pile. The wood is set on fire. After some time when fire dies out, wood charcoal is left behind. The other substances are -wood tar, pyroligneous acid and wood gas.
Selina Concise Chemistry Class 8 ICSE Solutions - Water 7

(d) 60 carbon atoms are arranged in spherical structure in Buck minster fullerences.

Question 7.
(a) Descirbe the formation of coal,
(b) Name four types of coal with percentage of carbon present in each, with uses.
Answer:
(a) Formation of coal:- The formation of coal took millions of years. Coal was formed by the bacterial decomposition of ancient vegetable matter hurried under successive layers of the earth. Under in action of high temperature and pressure, and in the abcence of air, the decayed vegetable matter converted into coal.
(b) Types of Coal:

  1. Peat: It is light brown in colour and contains only 50 – 60% carbon. It is the most inferior form of coal.
  2. Lignite: it contains more than 60% carbon. It is brown in colour and harder than peat.
  3. Bituminous: It has 90%, 80%, 70 – 75% carbon contents. Bituminous coal is the most common variety of coal and used as house hold coal.
  4. Anthracite: It is the purest variety of coal. Its carbon contents vary between 92 – 98%. It is hard, dense and black, difficultto ignite.

Uses of coal:

  1. Coal is used as both domestic and industrial fuel.
  2. It is used to prepare coke, coal gas and coal tar.

Question 9.
Name the products formed when:

(a) wood is burnt in the absence of air.
(b) bone is heated in the absence of air.
(c) diamond is burnt in air at 900°C.
(d) graphite is subjected to high pressure and 3000°C temperature.
Answer:
(a) Wood charcoal is formed when wood is burnt in limited supply of air.
(b) Bone charcaol, bone oil and organic compound pyridine.
(c) Carbon dioxide.
(d) Artificial diamond.

Question 9.
Give two uses for each of the following:

(a) coal
(b) coke
(c) wood charcoal
(d) sugar charcoal
(e) bone charcoal
(f) lampblack
Answer: 
(a) Uses of coal

  • It is used as both a domestic and an industrial fuel.
  • It is used to prepare coke, coal gas and coal tar.

(b) Uses of coke

  • Coke is used as a smokeless fuel, in smelting furnaces.
  • It is used in the manufacturing of water and producer gas.

(c) Uses of wood charcoal:

  • Wood charcoal is used as a fuel.
  • It is an important constituent of gun powder.

(d) Sugar charcoal:

  • Sugar charcoal is mostly used as a reducing agent.
  • It is used to decolourise coloured solutions.

(e) Bone charcoal:

  • It is extensively used to decolourise cane-sugar in the process of manufacturing sugar.
  • It is also used in the manufacture of large number of phosphorous compounds.

(f) Uses of lamp black:

  • It is used in making black shoe polish.
  • It is used in the manufacture of tyres and gun powder.

Question 10.
Give balanced equations for the following chemical reactions:

(a) wood charcoal and cone, nitric acid
(b) coke and steam
(c) wood charcoal and lead monoxide.
Answer:
Selina Concise Chemistry Class 8 ICSE Solutions - Water 8

Exercise – III

Question 1.
(a) Name the chemicals required for the preparation of carbon dioxide in the laboratory.
(b) How will you collect the gas?
(c) Write the balanced chemical equation for the above reaction.
(d) Draw a labelled diagram for the preparation of CO2 in the laboratory.
(e) Why is sulphuric acid not used for the preparation of carbon dioxide in the laboratory?
Answer:
(a) Calcium carbonate and dilute hydrochloric acid.
(b) By upward displacement of air.
(c) CaCO3 + 2HCl → CaCl2 + H2O + CO2.
(d) Laboratory preparation of carbon dioxide
Selina Concise Chemistry Class 8 ICSE Solutions - Water 9

(e) Dilute sulphuric acid reacts with calcium carbonate. But it is not used because the calcium sulphate which is formed during the reaction is insoluble in water. It covers the marble chips and stops the reaction.
Selina Concise Chemistry Class 8 ICSE Solutions - Water 10

Question 2.
Write the balanced chemical equations for the preparation of carbon dioxide by:
(a) heating calcium carbonate.
(b) the action of acetic acid on sodium bicarbonate.
(c) the action of dilute sulphuric acid on sodium bicarbonate.
Answer:
Selina Concise Chemistry Class 8 ICSE Solutions - Water 11

Question 3.
What happens when:
(a) a lit splinter is introduced into a jar containing carbon dioxide?
(b) moist blue litmus paper is placed in a jar containing carbon dioxide?
(c) carbon dioxide is passed through lime water first in small amounts and then in excess?
(d) a baking mixture containing baking powder is heated?
(e) a soda water bottle is opened?
Answer:
(a) Lit splinter extinguishes.
(b) Blue litmus paper turns red.
(c) When CO2 is passed through lime water in small amount, it turns milky, when passed in excess milkiness disappears.
(d) Carbon dioxide is formed.
(e) When the pressure is released the bottled gas escapes with a bristling effervescence that ads fizz to the drink.

Question 4.
Give reasons for the following:
(a) An excess of carbon dioxide increases the temperature of the earth.
(b) Soda acid and foam types of fire extinguisher are not used for extinguishing electrical fires.
(c) Solid carbon dioxide is used for refrigeration of food.
Answer:
(a) Excess carbon dioxide increases the temperature of the earth. Due to the rise in temperature ice in the polar regions may melt causing floods in coastal regions island.
(b) In both of these fire extinguishers, the solutions are prepared in water, which conducts electricity. As a result, an electric shock might result, which might lead to short-circuiting and another fire.
(c) Solid carbon dioxide serves as a coolant and refrigeration for preserving food articles.

Question 5.
What is a fire extinguisher? What is the substance used in the modern type of fire extinguishers? How is it an improvement over the soda acid-type and the foam-type fire extinguishers?
Answer:
Fire Extinguisher— Fire extinguishers are a device in which carbon dioxide is produced in different forms for use as the extinguishing agent. It is a modem type of fire extinguisher in which liquid carbon dioxide is stored in a steel cylinder under pressure. Soda-acid and foam types of extinguisher cannot be used for extinguishing fire as they prepared in water, which conducts electricity and there can be short-circuiting, causing another fire.

Question 6.
Explain the term ‘greenhouse effect’. How can it be both beneficial and harmful for life on earth ?
Answer:
Green house effect— The trapping of the earth’s radiated energy by carbon dioxide present in air, so as to keep the earth warm, is called ‘green house effect’.
Green house is beneficial because this principle is applied to grow plants in colder regions.
Carbon dioxide increases the temperature of atmosphere. Due to rise in temperature; ice in the polar regions may melt, causing floods. So it is harmful for life on earth.

Question 7.
What steps should be taken to balance carbon dioxide in the atmosphere ?
Answer:
As global warming will cause an unbalanced ecological system, serious efforts should be made to balance the percentage of carbon dioxide in the atmosphere. Some of these steps are:

  • Growing more trees and plants.
  • Using smokeless sources of energy like solar energy, biogas, etc.
  • Using filters in the chimneys of factories and power houses.

Question 8.
State three ways by which carbon dioxide gas is added into the atmosphere.
Answer:

  1. By planting more trees.
  2. By combustion of fuels
  3. By decay of dead animals, plants and plants products.

Exercise – IV

Question 1.
Fill in the blanks:

(a) Carbon monoxide is formed when carbon is burnt in a limited supply of air or oxygen.
(b) Carbon monoxide bums in air with a pale blue flame to form carbon dioxide.
(c) Carbon monoxide is a products of incomplete combustion.
(d) A mixture of 95% oxygen and 5% carbon dioxide is called carbogen
(e) Carbon dioxide is used as a reducing agent in the extraction of pure metals from their corresponding ores.

Question 2.
Match the following.
Selina Concise Chemistry Class 8 ICSE Solutions - Carbon and Its Compounds 1
Answer:
Selina Concise Chemistry Class 8 ICSE Solutions - Water 12

Question 3.
How is carbon monoxide gas formed?
Answer:
Mostly carbon monoxide is formed when a large amount of carbon or its compounds is burnt in a limited supply of air or oxygen.
Selina Concise Chemistry Class 8 ICSE Solutions - Water 13

Question 4.
State the poisonous nature of carbon monoxide?
Answer:
Carbon monoxide is a highly poisonous gas. If air containing 0.5% carbon monoxide by volume is inhaled, death can result This is because carbon monoxide combines with the haemoglobin present in the blood cells of our body to form a stable compound called carboxyl-haemoglobin. This does not allow to absorb of oxygen. Thus depriving our body cells of oxygen. This cause obstruction in respiration and causes death.

Question 5.
Give two uses of carbon monoxide.
Answer:
Uses of carbon monoxide:

  • Carbon monoxide is a strong reducing agent.
  • Carbon monoxide is used in the extraction of pure metals from their ores.

Question 6.
Why is carbon monoxide called a silent killer?
Answer:
Carbon monoxide is produced by burning coal or wood in a limited supply of air. Since the gas is colourless and a barely detectable smell, people do not feel it and it can be proved as a silent killer.

Question 7.
Explain the reducing action of carbon monoxide.
Answer:
Reducing action of carbon- monoxide: Carbon monoxide is a strong reducing agent. It reduces the oxides of the less active metals to their respective metals and itself gets oxidised to carbon dioxide.
Selina Concise Chemistry Class 8 ICSE Solutions - Water 14

Question 8.
Write two remedies for carbon monoxide poisoning.
Answer:

  1. The victim should immediately be brought out into the open.
  2. The victim should be given artificial respiration with carbogen.

Question 9.
Complete the reactions and balance them.
(a) CuO + CO →
(b) Fe2O2 + CO →
Answer:

Selina Concise Chemistry Class 8 ICSE Solutions - Water 15

Selina Concise Chemistry Class 8 ICSE Solutions – Water

Selina Concise Chemistry Class 8 ICSE Solutions – Water

ICSE Solutions  Selina ICSE Solutions  ML Aggarwal Solutions

ICSESolutions.com provides step by step solutions for Selina Concise ICSE Solutions for Class 8 Chemistry Chapter 8 Water. You can download the Selina Concise Chemistry ICSE Solutions for Class 8 with Free PDF download option. Selina Publishers Concise Chemistry for Class 8 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

Selina Class 8 Chemistry ICSE SolutionsPhysicsBiologyMathsGeographyHistory & Civics

Selina Concise ICSE Solutions for Class 8 Chemistry Chapter 8 Water

Points to Remember:

  • Water is the source of life for all living beings.
  • Water occurs in all the three states of matter i.e. ice, liquid water and water vapours.
  • Water found in nature (i) oceans and seas (ii) rivers and lakes (iii) springs and wells (iv) rain.
  • Rainwater is the purest form of water. Sea water is very impure.
  • Potable water should be free from suspended impurities and harmful germs.
  • Water is a compound, with the molecular formula is H2O.
  • The boiling point of water is 100°C and the freezing point is 0°C.
  • 0°C is also called tripple point, because water can exist in all its three states.
  • The specific heat of water is higher than that of any other liquid. It is used as a cooling agent.
  • Water has minimum volume and maximum density at 4°C. This is called anomalous behaviour of water.
  • Water is an universal solvent. The gases dissolved in water have biological importance. They enable aquatic life to sustain itself.
  • Water may be ‘hard or soft’. Hardness of water can be removed by boiling or by chemical treatment.
  • Water pollution is a serious problem.
  • Industrial and agriculture processes, nuclear and thermal plants pollute water.

Exercise – I

Question 1.
Name the four main sources of water.
Answer:

  1. Oceans
  2. Seas
  3. Rivers
  4. Lakes

Question 2.
State the importance of water cycle in nature.
Answer:
(i) Water cycle helps in regulating weather on the earth.
(ii) Water cycle makes water available in various forms on the earth.

Question 3.
Why is water very precious for all living beings?
Answer:
Water is one of the most precious substances for the existence of life. Since life on the earth began in the oceans, and since no living thing can survive without water, it is rightly called the source of life.
Water forms a large part of the body mass of all living organisms — 90% of human blood is water. Water has the ability to dissolve a number of substances. Therefore, it serve as the liquid medium in which all reactions within the living body take place.
Fruits and vegetables contain water in them. Even dry-looking substances like wood, peas, beans, grams, etc., contain some amount of water.

Question 4.
Name the two gases from which water is formed. What is the chemical composition of these two gases in water? Give the molecular formula of water?
Answer:
Oxygen and hydrogen
Chemical composition = H2 and O2 proportion 2:1
Molecular formula = H2O

Question 5.
What is the effect on the boiling point of water when
(a) pressure is increased
(b) impurity is added
Answer:
(a) The boiling point of water increases with an increase, in pressure.
(b) Any impurity present in water lowers its freezing point and raises its boiling point.
For example, salt is added to ice to lower its melting point. Such a mixture is called a freezing mixture. The melting is called a freezing mixture is about -15° C.

Question 6.
Give reasons:
(a) Water is used as a cooling agent
(b) Water pipes burst in severe winters.
(c) It is difficult to cook in hills compared to plains.
(d) Ice floats on water.
(e) Seawater does not freeze at 0°C.
Answer:
(a) Water has high specific heat. Water neither heats up nor cools down quickly. This property makes water as an excellent cooling agent.
(b) Water pipes bursts in severe winter because the water inside I the pipes freezes and increases its volume.
(c) Water boils at a lower temperature in the hills, where the atmospheric pressure is lower than in the plains. This is why it takes a longer time to cook in hilly regions.
(d) Ice has a low density as compared to water. Water has a maximum density at 4°C. That is why ice floats on water.
(e) There are impurities dissolved in seawater which increases the freezing point. That is why seawater does not freeze at 0°C.

Question 7.
How does anomalous expansion of water help aquatic organisms in cold climates?
Answer:
The anomalous expansion of water helps in survivals of water animals in very cold climates. Initially when temperature of water falls, it becomes heavier and sinks down. This process continues till 4°C. Then after this expansion takes place. The surface layer of water gets freezed. Ice being bad conductor of heat does not allow loss of heat from the water below and results in survival of water animals.

Exercise – II

Question 1.
Explain the terms:
(a) Solution (b) Solute (c) Solvent.
Answer:
(a) Solution: “A homogeneous mixture of two or more substances can be varied is called a solution”.
(b) Solute: A substance which dissolves in a other substances to form a solution is called solute. Solute is smaller quantity in solution.
Or
“Substance which is dissolved in solvent.” is called Solute. Solute is smaller quantity in solution.
(c) Solvent: A solvent is a medium in which a solute dissolves. It is in large quantity in solution.
Solution = Solute + Solvent

Question 2.
What is meant by
(a) Unsaturated (b) Saturated and
(c) Supersaturated solutions.
Answer:
(a) Unsaturated solutions — A solution in which more of the solute can be dissolved at a given temperature is called an unsaturated solution.
(b) Saturated solutions — A solution that cannot dissolve any more of the solute at a given temperature is called a saturated solution.
(c) Supersaturated solutions — A solution that contains more solute than it can hold at room temperature is called supersaturated solution.

Question 3.
How do the solubility of a solid and a gas affected by –
(a) Increase in temperature
(b) Increase in pressure
Answer:
(a) Solubility of a solid solute generally increases with an increase in temperature. This makes it possible to prepare supersaturated solutions.
Solubility of a gas decreases with an increase in temperature.

(b) Pressure has practically no effect on the solubility of a solid (solute) in water.
In the case of gases, the amount of a gas dissolved in water increases with an increase in pressure.

Question 4.
Differentiate between:
(a) Solution and suspension
(b) Suspension and colloid
Answer:
(a) Solution and suspension

Solution

  1. It is an example of homogeneous mixture.
  2. Particle size less than 10-10m
  3. Transparent
  4. Solute particles can not be filtered. Solution pass easily through filter paper.

Suspension

  1. It is an example of heterogeneous mixture.
  2. Particle size greater team 10-7 m
  3. Opaque
  4. Particles of suspension do not pass through filter paper.

(b) Suspension and colloids

Suspension

  1. Heterogeneous
  2. Particle size greater than 10-7 m.
  3. Opaque.
  4. Particles are visible.
  5. Particles of suspension settle at the bottom of the container.
  6. Particles of suspension do not pass through filter paper.

Colloid

  1. Heterogeneous.
  2. Particles size between 10-10 to 10-7m.
  3. Translucent.
  4. Particles can be seen with the help of a powerful microscope.
  5. Particles of colloids do not settle.
  6. Colloidal particles pass easily through ordinary filter paper but do not pass through ultra filters.

Question 5.
Define: ‘water of crystallisation’. Give two examples with formulae.
Answer:
The fixed amount of water which is in loose chemical combination with a salt in its crystal is called water of crystallisation. Examples:
Selina Concise Chemistry Class 8 ICSE Solutions - Water 1

Question 6.
Give two examples for each of the following:
(a) Hydrated substances
(b) Crystalline anhydrous substances
(c) Drying agents
(d) Deliquescent substances
(e) Efflorescent substances
(f) Colloids
(g) Solvents other than water.
Answer:
(a) Washing soda, Glauber’s salt (Na2SO4.10H2O)
(b) Common salt (NaCl), potassium nitrate (KNO3), sugar (C12H22O111) etc.
(c) Concentrated sulphuric acid (H2SO4), phosphorus pentoxide (P2O5), quicklime (CaO)
(d) Caustic soda (NaOH), crystalline-magnesium chloride (MgCl2), calcium chloride (CaCl2), Iron (III) chloride etc.
(e) Washing soda and glauber’s salt (Na2SO4.10 H2O)
(f) Milk, blood, smoke, jellies, butter, ink etc.
(g) Acetone, ethanol, turpentive

Question 7.
What do you observe when:
(a) Blue vitriol is heated ?
(b) Washing soda is exposed to air ?
(c) Blue litmus solution is added to water ?
Answer:
(a) Blue vitriol is blue in colour as it contains 5 molecules of water of crystallisation (CuSO^HjO). When it is heated, it loses water of crystallisation and becomes an hydrous CuS04 which is grey-white in colour.
(b) Washing soda (Na2CO3.10H2O) is a white crystalline substance and on exposure to air it gets changed to white powder.
(c) Pure water is neutral to litmus which means that no change in the colour of blue or red litmus solution is observed when 1 treated with water.

Question 8.
Give reason:
(a) Silica gel pouches are kept in unused water bottles.
(b) Table salt becomes moist during rainy season.
(c) On opening a bottle of a cold drink, a fizz sound is heard.
Answer:
(a) Silica get pouches are very commonly used to absorb moisture and to keep things dry. They are often kept in unused water bottles, with camera lenses etc. to keep them dry. These pouches are ideal to reuse throughout, in places at home where there is excess of moisture.

(b) On exposure to air, table salt (NaCl) turns moist and ultimately forms a solution especially during rainy season because it contains impurities like magnesium chloride and calcium chloride which are deliquescent. Sodium chloride is not deliquescent.

(c) The cold drink bottles contain carbon dioxide and are bottled under high pressure i.e. they contain a large amount of gas dissolved in them and on opening a bottle we hear a fizz sound, this is because of the solubility of CO2 gas in it and pressure in it.

Question 9.
Give balanced chemical equations for the reaction of water with
(a) Sodium (b) Iron
(c) Carbon dioxide (d) Sodium oxide
Answer:
Selina Concise Chemistry Class 8 ICSE Solutions - Water 2

Question 10.
What is metal activity series ?
Answer:
The arrangement of metals in the decreasing order of their reactivity in the form of a series is called the activity or reactivity series of metals.
Selina Concise Chemistry Class 8 ICSE Solutions - Water 3

Question 11.
Name the gas produced when
(a) steam is passed over hot coke.
(b) chlorine is dissolved in water and exposed to sunlight
(c) a piece of calcium is added to water.
(d) when fossil fuel is burnt,
Answer:
(a) Water gas
(b) Oxygen
(c) Hydrogen
(d) Carbon dioxide

Exercise – III

Question 1.
Define:
(a) Soft water
(b) Hard water
Answer:
(a) Soft water: The water present in different natural sources has different substances dissolved in it. The water drawn from certain sources forms a lather with soap rather easily. Such water is called soft water.
(b) Hard water: Water obtained from various sources does not easily form a lather with soap, rather it forms a white sticky scum or a precipitate. This water is called hard water.

Question 2.
(a) Name the compounds responsible for
(i) temporary hardness
(ii) permanent hardness of water
(b) Suggest one method for the removal along with the reactions for
(i) temporary hardness
(ii) permanent hardness of water
Answer:
(a) (i) Temporary hard water— Water, which has bicarbonates of calcium and magnesium dissolved in it, is temporary hard water. This kind of hardness is easily removed by boiling.
(ii) Permanent hard water— Water, which has sulphates and chlorides of calcium and magnesium dissolved in it, is called permanent hard water. This hardness cannot be removed by boiling.

(b) Removal of the hardness of water:
(i) Temporary hardness—
By Boiling— This method helps to remove only the temporary hardness of water. When temporary hard water is boiled, the bicarbonates of calcium and magnesium break up to form their insoluble carbonates.
These can be filtered out so that water becomes soft.
Selina Concise Chemistry Class 8 ICSE Solutions - Water 4
(ii) Removal of hardness of permanent hardness of water—
By Adding sodium carbonate (washing soda)
Permanent hardness of water is removed when water is treated with a small quantity of sodium carbonate.
It reacts with the soluble chlorides and sulphates of calcium and magnesium to form their insoluble carbonates. These can be removed by filtration and then the water becomes soft. Sodium sulphate or sodium chloride formed after the reaction does not affect the soap.
Selina Concise Chemistry Class 8 ICSE Solutions - Water 5

Question 3.
Name three water-borne diseases.
Answer:
(i) Cholera (ii) Typhoid (iii) Hepatitis

Question 4.
What are the main causes of water pollution? How can it be controlled?
Answer:
Main causes of water pollution are:

  • Chemical waste, industrial waste and agricultural processes.
  • Thermal waste from nuclear and thermal power plants.
  • Sewage and garbage.

Prevention of water pollution:

  • Domestic sewage should be treated before being discharged into rivers.
  • Using of non-biodegradable substances like detergents should be stopped.
  • Trees and plants must be planted along the banks of rivers.
  • Purification of water bodies should be carried out.
  • The waste products of industries should be treated before they are discharged into rivers.

Question 5.
Give reasons:
(a) Alcohol is mixed with water and is used in car radiators.
(b) Icebergs float on ocean water.
(c) Carbonated drinks are bottled under high pressure.
Answer:
(a) Alcohol is mixed with the water used in car radiators to prevent it from freezing ki cold weather. Because it lowers the freezing point of water.
(b) Ice bergs float in ocean water because density of ice is less than water.
(c) Carbonated drinks are bottled under high pressure because the solubility of carbon dioxide increases with pressure.

OBJECTIVE TYPE QUESTIONS

1. Fill in the blanks:

(a) Water has maximum density and minimum volume at 4°C.
(b) Freezing mixture contains ice and salt.
(c) The solubility of a gas in water increases with rise in temperature and decreases with rise in pressure.
(d) Rain water is the purest form of natural water.
(e) Use of excessive fertilizers by farmers causes water pollution.
(f) Boiling removes the temporary hardness of water.
(g) Water turns the colour of anhydrous copper sulphate blue.
(h) Water turns the colour of anhydrous copper sulphate scum.

2. Give one word/words for the following statements:

(a) Water fit for human consumption potable water.
(b) The harmful substances dissolved in water impurities.
(c) The change of states of water from one form to another water cycle.
(d) The gaseous form of water found in air – water vapours.
(e) A mixture of common salt and ice – freezing mixture.
(f) A substance which does not contain water anhydrous substances.
(g) A property due to which a substance absorbs water without dissolving hygroscopic.
(h) Water molecules in loose chemical combination with other substances water of crystallisation.

MULTIPLE CHOICE QUESTIONS

1. Two gases found dissolved in natural water are
(a) oxygen and carbon dioxide
(b) hydrogen and oxygen
(c) sulphur dioxide and hydrogen
(d) chlorine and ammonia

2. Temporary hardness of water can be removed by
(a) filtering
(b) boiling
(c) loading
(d) none of the above

3. The ultimate source of all water on the earth is
(a) oceans and seas
(b) spring and wells
(c) rivers and lakes
(d) rain

4. Colloids have the particle size range between
(a) 10-7 to 10-10 m
(b) 10-10 to 10-12 m
(c) 10-7 to 10-5 m
(b) 10-12 to 10-15 m

Selina Concise Chemistry Class 8 ICSE Solutions – Language of Chemistry

Selina Concise Chemistry Class 8 ICSE Solutions – Language of Chemistry

ICSE Solutions  Selina ICSE Solutions  ML Aggarwal Solutions

ICSESolutions.com provides step by step solutions for Selina Concise ICSE Solutions for Class 8 Chemistry Chapter 5 Language of Chemistry. You can download the Selina Concise Chemistry ICSE Solutions for Class 8 with Free PDF download option. Selina Publishers Concise Chemistry for Class 8 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

Selina Class 8 Chemistry ICSE SolutionsPhysicsBiologyMathsGeographyHistory & Civics

Selina Concise ICSE Solutions for Class 8 Chemistry Chapter 5 Language of Chemistry

Points to Remember:

  • The valency of an element is the number of electrons donated or accepted by its ‘atom’ during chemical combination.
  • There are some elements with more than one valency e.g., iron, copper, tin, lead.
  • Two or more different non-metals that collectively accept or donate one or more electrons and become negatively or positively charged in the process are called radicals.
  • A chemical reaction involves the transformation of original substance into an altogether new substance(s).
  • A chemical reaction can be represented with the help of the symbols or the formulae of the elements and the compounds taking part in that reaction. This gives a chemical equation.
  • Certain necessary conditions for a chemical reaction to happen are — close contact, solution form, heat, light and catalyst.
  • Characteristics of chemical reactions are — change of colour, evolution of a gas, formation of a precipitate, change of state, change of smell and evolution/absorption of heat.
  • A complete chemical equation symbolically represents the reactants, products and their physical states.
  • The substances that react with each other are called reactants and they are represented on the left hand side of the equation. The substances that are formed as a result of the reaction are called products. They are represented on the right hand side of the equation.
  • A chemical equation needs to be balanced to make it follow the law of the conservation of mass.
  • The law of conservation of mass states that mass can be neither created nor destroyed, it can only be transformed from one form to another.
  • A chemical equation gives both qualitative and quantitative information about the reactants and products.

ACTIVITY 1
Write the names and symbols of the first twenty elements that you have studied in class VI & VII.
Answer:
Selina Concise Chemistry Class 8 ICSE Solutions - Language of Chemistry 1

ACTIVITY 2
Write the molecular formulae of:

  1. Copper oxide
  2. Iron (III) chloride
  3. Sodium hydroxide
  4. Iron (II) sulphide
  5. Lead (II) oxide
  6. Hydrogen nitrate (nitric acid)
  7. Hydrogen sulphate (sulphuric acid)
  8. Calcium hydroxide
  9. Magnesium carbonate
  10. Ammonium carbonate

Answer:

  1. Copper oxide – CuO
  2. Iron (III) chloride – FeCl3
  3. Sodium hydroxide – NaOH
  4. Iron (II) sulphide – FeS
  5. Lead (II) oxide – PbO
  6. Hydrogen nitrate (nitric acid) – HNO3
  7. Hydrogen sulphate (sulphuric acid) – H2SO4
  8. Calcium hydroxide – Ca(OH)2
  9. Magnesium carbonate – MgCO3
  10. Ammonium carbonate – (NH4)2CO3

ACTIVITY 3
Write the molecular formula for each of the following compounds:

  1. Sulphur trioxide
  2. Iron (II) sulphide and
  3. Ammonia

Find the number and names of elements present in them and calculate their molecular masses.
Answer:
1. Sulphur trioxide

  1. A molecule of sulphur trioxide is represented by the formula SO3.
  2. The elements present in it are sulphur dioxide and oxygen.
  3. One molecule of sulphur trioxide has one atom of sulphur and three atoms of oxygen.
  4. Molecular mass of sulphur trioxide (SO3)
    = 32 + 3 x 16
    = 32 + 48 = 80 amu.

2. Iron (II) sulphide

  1. A molecule of iron (II) sulphide is represented by the formula FeS.
  2. The elements present in it are iron and sulphur.
  3. One molecule of iron (II) sulphide has one atom of iron and one atom of sulphur.
  4. Molecular mass of iron (II) sulphide (FeS)
    = 55.5 + 32
    = 87.5 amu.

3. Ammonia

  1. A molecule of ammonia is represented by the formula NH3.
  2. The elements present in it are nitrogen and hydrogen.
  3. One molecule of ammonia has one atom of nitrogen and three atoms of hydrogen.
  4. Molecular mass of ammonia (NH3)
    = 14 + 3 x 1
    = 14 + 3
    = 17 amu.

Exercise

Question 1.
Define:
(a) Radical
(b) Valency
(c) Molecular formula
Answer:
(a) Radical: A radical is an atom of an element or a group of atoms of different elements that behaves as a single unit with a positive or negative charge on it.
(b) Valency: It is the number of electrons donated or accepted by the valence shell of an atom during chemical combination.
(c) Molecular formula: It is a symbolic representation of a molecule. It shows the number of atoms of each element present in it. These atoms combine in the whole numbers to form the molecule.

Question 2.
Give the symbols and valencies of the following radicals:
(a) Hydroxide (b) Chloride
(c) Carbonate (d) ammonium
(e) Nitrate
Answer:
Selina Concise Chemistry Class 8 ICSE Solutions - Language of Chemistry 2

Question 3.
Write the molecular formula for the oxide and sulphide of the following elements.
(a) Sodium (b) Calcium
(c) Hydrogen
Answer:
(a) Sodium oxide Na2O
Sodium sulphide Na2S
(b) Calcium oxide CaO
Calcium sulphide CaS
(c) Hydrogen oxide H2O
Hydrogen sulphide H2S

Question 4.
Write the molecular formulae for the following compounds and name the elements present.
(a) Baking soda (b) Common salt
(c) Sulphuric acid (d) Nitric acid
Answer:
(a) Baking soda — NaHCO3
Elements present in Baking soda are sodium, hydrogen, oxygen and carbon.
(b) Common salt — NaCl
Element present are: Sodium and chlorine.
(c) Sulphuric acid — H2SO4
Element present are: Hydrogen, sulphur and oxygen.
(d) Nitric acid — HNO3
Elements present are: Hydrogen, nitrogen and oxygen.

Question 5.
The valency of aluminium is 3. Write the valency of other radicals present in the following compounds.
(a) Aluminium chloride
(b) Aluminium oxide
(c) Aluminium nitride
(d) Aluminium sulphate
Answer:
(a) Aluminium chloride — (AlCl3) here valency of Al is 3.
Other radical – Chloride (Cl)
Valency of chloride = 1
(b) Aluminium oxide — (Al2O3)
Here valency of Al is 3
Other radical presents = oxide (O2-)
Valency of O2- = 2
(c) Aluminium nitride — (Al N)
Here valency of aluminium = 3
Another radical = Nitride (N3-)
Valency of nitride (N3-) = 3
(d) Aluminium sulphate — Al2(SO4)3
Here valency of aluminium is 3
Another radical = Sulphate (SO42-)
Valency of (SO42-) = 2

Question 6.
What is variable valency? Give two examples of elements showing variable valency.
Answer:
Certain elements exhibit more than one valency, which means they show variable valency.
Ferrous is written as Iron (II) and Ferric is written as Iron (III).

MetalRadicalsValency
IronFerrous [Iron (II)]
Ferric [Iron (III)]
2
3
CopperCuprous [Copper (I)]
Cupric [Copper (II)]
1
2

Question 7.
(a) What is a chemical equation?
(b) Why it is necessary to balance a chemical equation?
(c) What are the limitations of a chemical equation?
Answer:
(a) Chemical Equation— A chemical equation is the symbolic representation of a chemical reaction using the symbols and the formulae of the substances involved in the reaction.
(b) A chemical equation needs to be balanced so as to make the number of the atoms of the reactants equal to the number of the atoms of the products.
(c)

  1. It does not inform about the physical states of the reactants and the product i.e. whether they are solids, liquids, and gases.
  2. It does not inform about the concentration of reactants and products.
  3. It does not inform about the time taken for the completion of the reaction.
  4. It does not inform about the rate at which a reaction proceeds.
  5. It does not inform about the heat changes during the reaction i. e. whether the heat is given out or absorbed.
  6. It does not inform about the conditions such as temperature, pressure, catalyst, etc. which affect the reaction.
  7. It does not inform about the nature of the reaction i.e. whether it is reversible or irreversible.

Question 8.
What are the ways by which a chemical equation can be made more informative?
Answer:
A chemical equation can give more information in the following ways:

  1. The physical state of the reactants and products can be indicated by putting (s) for solid, (l) for liquid, (g) for gas and (aq) for aqueous state.
  2. Evolution or absorption of heat during the reaction can be denoted by adding or subtracting a heat term on the product side.
  3. Temperature, pressure and catalyst can be indicated above the arrow (→ or =) separating the reactants and products.
  4. Concentration of reactants and products are indicated by adding word (dil) for dilute and (cone) for concentrated before their formulae.
  5. By the sign → or \(\rightleftharpoons \) information about irreversible and reversible reactions can be obtained.

Question 9.
State the law of conservation of mass.
Answer:
Law of conservation of mass: It states that mass can neither be created nor destroyed in a chemical reaction. During any change (physical or chemical), matter is neither created nor destroyed. However it may change from one form to another.
Selina Concise Chemistry Class 8 ICSE Solutions - Language of Chemistry 3
Experimental Verification of Law of Conservation of Mass

Requirements: H-shaped tube called Landolt’s tube, Sodium chloride solution, silver nitrate solution, etc.
Procedure: A specially designed H-shaped tube is taken. Sodium chloride solution is taken in one limb of the tube and silver nitrate solution in the other limb as shown in the figure.
Both the limbs are now sealed and weighed. Now the tubes is averted so that the solutions can mix up together and react chemically. The reaction takes place and a white precipitate of silver chloride is obtained.
Selina Concise Chemistry Class 8 ICSE Solutions - Language of Chemistry 4
The tube is weighed again. The mass of the tube is found to be exactly the same as the mass obtained before inverting the tube.
Thus, this experiment clearly verifies the law of conservation of mass.

Question 10.
Differentiate between:
(a) Reactants and products
(b) A balanced and an unbalanced chemical equation
Answer:
(a) Reactants and products

Reactants

  1. The substances that react with one another are called reactants.
  2. Reactants are written on the left-hand side of the equation.

Products

  1. The new substances formed are called products.
  2. Products are written on the right-hand side of the equation.

(b) A balanced and an unbalanced chemical equation

Balanced chemical

  1. A balanced chemical reaction is one in which the number of atoms of each element on the reactant side is equal to the number of atoms of that element on the product side.
  2. Ex- H2 + Cl2 → HCl

Unbalanced chemical

  1. The number of elements on the reactant side is not equal to the number of elements on the product side.
  2. Ex- H2 + Cl2 → 2HCl

Question 11.
Balance the following equations:
Selina Concise Chemistry Class 8 ICSE Solutions - Language of Chemistry 5
Answer:
Selina Concise Chemistry Class 8 ICSE Solutions - Language of Chemistry 6

Question 12.
12. Write balanced chemical equations for the following word equations:
(a) Iron + Chlorine → Iron (III) chloride
(b) Magnesium + dil sulphuric acid → Magnesium sulphate + water
(c) Magnesium + oxygen → Magnesium oxide
(d) Calcium oxide + water → Calcium hydroxide
(e) Sodium + chlorine → Sodium chloride
Answer:
(a) Iron + Chlorine → Iron (III) chloride
4Fe + 3Cl2 → 2F2Cl3
(b) Magnesium + dil sulphuric acid → Magnesium sulphate + water
2Mg + 2H2SO4 → 2MgSO4 + 2H2
(c) Magnesium + oxygen → Magnesium oxide
2Mg + O2 → 2MgO
(d) Calcium oxide + water → Calcium hydroxide
CaO + H2O → Ca(OH)2
(e) Sodium + chlorine → Sodium chloride
2Na + Cl2 → 2NaCl

Question 13.
What information do you get from the following chemical equation:
Zn(s) + 2HCl (dil) → ZnCl2 (aq) + H2(g)
Answer:
This gives zinc chloride and hydrogen. The word equation is:
Zinc + Hydrochloric acid → Zinc chloride + Hydrogen
Formulae for the products are ZnCl2 and H2

Selina Concise Chemistry Class 8 ICSE Solutions – Atomic Structure

Selina Concise Chemistry Class 8 ICSE Solutions – Atomic Structure

ICSE Solutions  Selina ICSE Solutions  ML Aggarwal Solutions

ICSESolutions.com provides step by step solutions for Selina Concise ICSE Solutions for Class 8 Chemistry Chapter 4 Atomic Structure. You can download the Selina Concise Chemistry ICSE Solutions for Class 8 with Free PDF download option. Selina Publishers Concise Chemistry for Class 8 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

Selina Class 8 Chemistry ICSE SolutionsPhysicsBiologyMathsGeographyHistory & Civics

Exercise

1. Fill in the blanks.

(a) Dalton said that atoms could not be divided
(b) An ion which has a positive charge is called a cation.
(c) The outermost shell of an atom is known as valence shell.
(d) The nucleus of an atom is very hard and dense.
(e) Neutrons are neutral particles having mass equal to that of protons.
(f) Isotopes are the atoms of an element having the same atomic number but a different mass number.

2. Write ‘true’ or ‘false’ for the following statements:

(a) An atom on the whole has a positive charge.
false
(b) The maximum number of electrons in the first shell can be 8.
false
(c) The central pad of the atom is called nucleus.
True.

3. Give the following a suitable word/phrase.

(a) The sub-atomic particle with negative charge and negligible mass.
(b) Protons and neutrons present in the nucleus.
(c) The electrons present in the outermost shell.
(d) Arrangement of electrons in the shells of an atom.
(e) The number of protons present in the nucleus of an atom.
(f) The sum of the number of protons and neutrons of an atom.
(g) Atoms of same element with same atomic number but a different mass number.
(h) The smallest unit of an element which takes part in a chemical reaction.

Answer:

(a) Neutron
(b) Mass number
(c) Valency
(d) Orbits or Valence shells
(e) Atomic number
(f) Mass number
(g) Isotopes
(h) Atom

4. Multiple Choice Questions

(a) The outermost shell of an atom is known as

  1. valency
  2. valence electrons
  3. nucleus
  4. valence shell

(b) The number of valence electrons present in magnesium is

  1. two
  2. three
  3. four
  4. five

(c) The sub atomic particle with negative charge is

  1. proton
  2. neutron
  3. electron
  4. nucleon

(d) If the atomic number of an atom is 17 and mass number is 35 then number of neutron will be

  1. 35
  2. 17
  3. 18
  4. 52

(e) The number of electrons in an atom is equal to number of

  1. protons in a neutral atom
  2. neutrons in a neutral atom
  3. nucleons in a neutral atom
  4. none of the above

(f) The sum of number of protons and number of neutrons present in the nucleus of an atom is called its

  1. mass number
  2. atomic number
  3. number of electrons
  4. all of the above

Question 5.
Name three fundamental particles of the atom. Give the symbol with charge, on each particle.
Answer:
The fundamental particles of the atom are: electrons, protons and neutrons.

ParticleSymbolCharge
electrone-1 or 1.602 x 10-19 C. Where -1 represent its one unit negative electrical charge
protonp++ 1 or 1.602 x 10-19 C. Where +1 represents one unit +ve electrical charge.
neutronno0

Question 6.
Define the following terms:
(a) Atomic number
(b) Mass number
(c) Nucleons
(d) Valence shell
Answer:
(a) Atomic number: Atomic number refers to the number of protons present in an atom. It is denoted by Z. Example: An atom of oxygen contains 8 proton Therefore its atomic number is 8.
(b) Mass number: Mass number refers to the sum of the number of protons and neutrons present in the nucleus of an atom and denoted by A Mass number = Number of protons + Number of neutrons.
(c) Nucleons: The protons and neutrons collectively are known as nucleons.
(d) Valence Shell: The outermost shell of an atom is known as its valence shell.

Question 7.
Mention briefly the salient features of Dalton’s atomic theory (five points).
Answer:
Salient features of Dalton’s atomic theory:

  1. Matter consists of very small and indivisible particles called atoms, which can neither be created nor can be destroyed.
  2. The atoms of an element are alike in all respects i.e. size, mass, density, chemical properties but they differ from the atoms of other elements.
  3. Atoms of an element combine in small numbers to form molecules of the element.
  4. Atoms of one element combine with atoms of another element in simple whole number ratio to form molecules of compounds.
  5. Atoms are the smallest units of matter that can take part in a chemical reaction during which only rearrangement of atoms takes place.

Question 8.
(a) What are the two main features of Rutherford’s atomic model?
(b) State its one drawback.
Answer:
(a) According to Rutherford’s model an atom consists of:

  1. The centrally located nucleus: The nucleus is a centrally located positively charged mass. The entire mass of the atom is concentrated in it. It is the densest part of the atom. Its size is very small as compare to the atom as a whole.
  2. The outer circular orbits: Electrons revolve in circular orbits (shell) in the space available around the nucleus. An atom is electrically neutral i.e., number of protons and electrons present in an atom are equal.

(b) Rutherford’s atomic model could not explain the stability of the atom as it is like a solar system, the sun is at the centre and the planets revolve around it, in an atom the electrons revolve around the centrally located nucleus containing protons.

Question 9.
What are the observations of the experiment done by Rutherford in order to determine the structure of an atom?
Answer:
Following were the observations made by Rutherford:

  1. Most of the alpha particle passed straight through the foil without any deflection from their path.
  2. A small fraction of them were deflected from their original path by small angles.
  3. Only a few particles bounced back.

Question 10.
State the mass number, the atomic number, number of neutrons and electronic configuration of the following atoms.
Selina Concise Chemistry Class 8 ICSE Solutions - Atomic Structure 1
Also, draw atomic diagrams for them.
Answer:
Selina Concise Chemistry Class 8 ICSE Solutions - Atomic Structure 2
Selina Concise Chemistry Class 8 ICSE Solutions - Atomic Structure 3

Question 11.
What is variable valency? Name two elements having variable valency and state their valencies.
Answer:
Variable valency: Some elements exhibit more than one valency. They are said to have variable valency, e.g. Iron, copper, tin, lead.
Iron         Fe       Fe2+ or Fe3+
Copper   cu        cu+ or cu2+

Question 12.
The atomic number and the mass number of sodium are 11 and 23 respectively. What information is conveyed by this statement?
Answer:
Atomic number = 11; No of protons = 11
Mass number = 23 = Number of protons + Number of neutrons.
No of neutrons = 23-11 = 12.

Question 13.
Draw the diagrams representing the atomic structures of the following:
(a) Nitrogen (b) Neon
Answer:
Selina Concise Chemistry Class 8 ICSE Solutions - Atomic Structure 4

Question 14.
Explain the rule with example according to which electrons are filled in various energy levels,
Answer:
The maximum number of electrons that can be present in any shell or orbit of an atom is given by the formula 2n2, where n is the serial number of the shell.
Therefore:
K shell, n = 1, no. of electrons = 2 x 12 = 2
L shell, n = 2, no. of electrons = 2 x 22 = 8
M shell, n = 3, no. of electrons = 2 x 32 = 18
N shell, n = 4, no. of electrons = 2 x 42= 32
Electrons are not accommodated in a given shell, unless the inner shells are filled.
That is, the shells are filled in a stepwise manner.
Example:
Selina Concise Chemistry Class 8 ICSE Solutions - Atomic Structure 5

Question 15.
The atom of an element is made up of 4 protons, 5 neutrons and 4 electrons. What is its atomic number and mass number?
Answer:
Protons = 4, neutrons = 5, electrons = 4
Atomic number = 4,
Mass number = 4 + 5 = 9

Question 16.
(a) What are the two main parts of which an atom is made of?
(b) Where is the nucleus of an atom situated ?
(c) What are orbits or shells of an atom ?
Answer:
(a)

  1. The centrally located nucleus
  2. The outer circular orbits.

(b) The nucleus is a centrally located positively charged mass.
(c) The circular orbits (shell present) in the space available around the nucleus on which electrons revolve are called orbits or shells of an atom.

Question 17.
What are isotopes? How does the existence of isotopes contradict Dalton’s atomic theory?
Answer:
Atoms of an element must have the same atomic number, but their mass number can be different due to the presence of a different number of neutrons. These atoms of an element having a different number of neutrons are called groups.
According to Dalton’s theory, all atoms of an element are similar to all respects, for example, they have the same shape, size etc. and have similar physical and chemical properties like mass, density and reactivity. Whereas isotopes of an element have atoms that are similar as they have same number of protons and electrons but differ in the number of neutrons. So, the isotopes have atoms that are not similar in all aspects.

Question 18.
Complete the table below by identifying A, B, C, D, E and F.
Answer:
Selina Concise Chemistry Class 8 ICSE Solutions - Atomic Structure 6

Selina Concise Mathematics Class 8 ICSE Solutions Chapter 19 Representing 3-D in 2-D

Selina Concise Mathematics Class 8 ICSE Solutions Chapter 19 Representing 3-D in 2-D

Selina Publishers Concise Mathematics Class 8 ICSE Solutions Chapter 19 Representing 3-D in 2-D

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

ICSESolutions.com provides step by step solutions for Selina Concise ICSE Solutions for Class 8 Mathematics Chapter 19 Representing 3-D in 2-D. You can download the Selina Concise Mathematics ICSE Solutions for Class 8 with Free PDF download option. Selina Publishers Concise Mathematics for Class 8 ICSE Solutions all questions are solved and explained by expert mathematic teachers as per ICSE board guidelines.

Selina Class 8 Maths SolutionsPhysicsChemistryBiologyGeographyHistory & Civics

Representing 3-D in 2-D Exercise 19 – Selina Concise Mathematics Class 8 ICSE Solutions

Question 1.
If a polyhedron has 8 faces and 8 vertices, find the number of edges in it.
Solution:
Faces = 8
Vertices = 8
using Eulers formula,
F + V – E = 2
8 + 8 – E = 2
-E = 2 – 16
E= 14

Question 2.
If a polyhedron has 10 vertices and 7 faces, find the number of edges in it.
Solution:
Vertices = 10
Faces = 7
Using Eulers formula,
F + V – E = 2
7 + 10 – E = 2
-E = -15
E = 15

Question 3.
State, the number of faces, number of vertices and number of edges of:
(i) a pentagonal pyramid
(ii) a hexagonal prism
Solution:
(i) A pentagonal pyramid
Number of faces = 6
Number of vertices = 6
Number of edges = 10

(ii) A hexagonal prism
Number of faces = 8
Number of vertices = 12
Number of edges = 18

Question 4.
Verily Euler’s formula for the following three dimensional figures:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 19 Representing 3-D in 2-D - 1
Solution:
(i) Number of vertices = 6
Number of faces = 8
Number of edges = 12
Using Euler formula,
F + V – E = 2
8 + 6 – 12 = 2
2 = 2 Hence proved.

(ii) Number of vertices = 9
Number of faces = 8
Number of edges = 15
Using, Euler’s formula,
F + V – E = 2
9 + 8 – 15 = 2
2 = 2 Hence proved.

(iii) Number of vertices = 9
Number of faces = 5
Number of edges = 12
Using, Euler’s formula,
F + V – E = 2
9 + 5 – 12 = 2
2 = 2 Hence proved.

Question 5.
Can a polyhedron have 8 faces, 26 edges and 16 vertices?
Solution:
Number of faces = 8
Number of vertices = 16
Number of edges = 26
Using Euler’s formula
F + V – E
⇒ 8 + 16 – 26 ≠ -2
⇒ -2 ≠ 2
No, a polyhedron cannot have 8 faces, 26 edges and 16 vertices.

Question 6.
Can a polyhedron have:
(i) 3 triangles only ?
(ii) 4 triangles only ?
(iii) a square and four triangles ?
Solution:
(i) No.
(ii) Yes.
(iii) Yes.

Question 7.
Using Euler’s formula, find the values of x, y, z.
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 19 Representing 3-D in 2-D - 2
Solution:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 19 Representing 3-D in 2-D - 3

Question 8.
What is the least number of planes that can enclose a solid? What is the name of the solid.
Solution:
The least number of planes that can enclose a solid is 4.
The name of the solid is Tetrahedron.

Question 9.
Is a square prism same as a cube?
Solution:
Yes, a square prism is same as a cube.

Question 10.
A cubical box is 6 cm x 4 cm x 2 cm. Draw two different nets of it.
Solution:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 19 Representing 3-D in 2-D - 4

Question 11.
Dice are cubes where the sum of the numbers on the opposite faces is 7. Find the missing numbers a, b and c.
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 19 Representing 3-D in 2-D - 5
Solution:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 19 Representing 3-D in 2-D - 6

Question 12.
Name the polyhedron that can be made by folding each of the following nets:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 19 Representing 3-D in 2-D - 7
Solution:
(i) Triangular prism. It has 3 rectangles and 2 triangles.
(ii) Triangular prism. It has 3 rectangles and 2 triangles.
(iii) Hexagonal pyramid as it has a hexagonal base and 6 triangles.

Question 13.
Draw nets for the following polyhedrons:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 19 Representing 3-D in 2-D - 8
Solution:
Net of hexagonal prism:
Selina Concise Mathematics Class 8 ICSE Solutions Chapter 19 Representing 3-D in 2-D - 9
Net of pentagonal pyramid: