Veerendra

Selina Concise Mathematics Class 8 ICSE Solutions Chapter 2 Exponents (Powers)

Selina Publishers Concise Mathematics Class 8 ICSE Solutions Chapter 2 Exponents (Powers)

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

ICSESolutions.com provides step by step solutions for Selina Concise ICSE Solutions for Class 8 Mathematics Chapter 2 Exponents (Powers). 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

Exponents Exercise 2A – Selina Concise Mathematics Class 8 ICSE Solutions

Question 1.
Evaluate:

Solution:

Question 2.
If 1125 = 3^m x 5ⁿ; find m and n.
Solution:

Question 3.
Find x, if 9 × 3^x = (27)^2x-3
Solution:

Exponents Exercise 2B – Selina Concise Mathematics Class 8 ICSE Solutions

Question 1.
Compute:


Solution:

Question 2.
Simplify:

Solution:

Question 3.
Evaluate:

Solution:

Question 4.
Simplify:

Solution:

Question 5.
Simplify:
(x^a+b)^a-b.(x^b+c)^b-c.(x^c+a)^c-a
Solution:

Question 6.
Simplify:

Solution:


Question 7.
(i) (a^-2)^-2. (ab)^-3
(ii) (xⁿy^-m)⁴ × (x³y^-2)^-n

Solution:

Question 8.
Show that:

Solution:

Question 9.
Evaluate:

Solution:

Question 10.
Evaluate:

Solution:

Question 11.
(m+n)^-1 (m^-1 + n^-1) = (mn)^-1
Solution:

Question 12.
Prove that:

Solution:

Question 13.
Find the values of n, when:

Solution:

Question 14.
Simplify:

Solution:

APlusTopper.com provides ICSE Class 10 History and Civics Previous Year Board Question Papers Solved Pdf Free Download with Solutions, Answers and Marking Scheme. Here we have given ICSE Class 10 History and Civics Solved Question Papers Last Ten Years. Students can view or download the ICSE Board 10th History and Civics Previous Year Question Papers with Solutions for their upcoming examination.

These ICSE Class 10 History and Civics Previous 10 Years Board Question Papers with Answers are useful to understand the pattern of questions asked in the board exam. Know about the important concepts to be prepared for ICSE Class 10 Board Exam and Score More marks.

Board – Indian Certificate of Secondary Education (ICSE), www.cisce.org
Class – Class 10
Subject – History and Civics
Year of Examination – 2020, 2019, 2018, 2017.

ICSE Class 10 History and Civics Solved Question Papers Last Ten Years

• ICSE History and Civics Question Paper 2019 Solved
• ICSE History and Civics Question Paper 2018 Solved
• ICSE History and Civics Question Paper 2017 Solved
• ICSE History and Civics Question Paper 2016 Solved
• ICSE History and Civics Question Paper 2015 Solved
• ICSE History and Civics Question Paper 2014 Solved
• ICSE History and Civics Question Paper 2013 Solved
• ICSE History and Civics Question Paper 2012 Solved
• ICSE History and Civics Question Paper 2011 Solved
• ICSE History and Civics Question Paper 2010 Solved
• ICSE History and Civics Question Paper 2009 Solved
• ICSE History and Civics Question Paper 2008 Solved
• ICSE History and Civics Question Paper 2007 Solved

We hope the ICSE Class 10 History and Civics Previous Years Question Papers Solved Last 10 Years Pdf Free Download with Solutions will help you. If you have any query regarding ICSE Class 10 History and Civics Solved Question Papers Last Ten Years with Answers, drop a comment below and we will get back to you at the earliest.

ICSE Previous Year Question Papers Class 10

APlusTopper.com provides ICSE Class 10 Physics Previous Year Board Question Papers Solved Pdf Free Download with Solutions, Answers and Marking Scheme. Here we have given ICSE Class 10 Physics Solved Question Papers Last Ten Years. Students can view or download the ICSE Board 10th Physics Previous Year Question Papers with Solutions for their upcoming examination.

These ICSE Class 10 Physics Previous 10 Years Board Question Papers with Answers are useful to understand the pattern of questions asked in the board exam. Know about the important concepts to be prepared for ICSE Class 10 Board Exam and Score More marks.

Board – Indian Certificate of Secondary Education (ICSE), www.cisce.org
Class – Class 10
Subject – Physics
Year of Examination – 2020, 2019, 2018, 2017.

ICSE Class 10 Physics Solved Question Papers Last Ten Years

• ICSE 2019 Physics Question Paper Solved
• ICSE 2018 Physics Question Paper Solved
• ICSE 2017 Physics Question Paper Solved
• ICSE 2016 Physics Question Paper Solved
• ICSE 2015 Physics Question Paper Solved
• ICSE 2014 Physics Question Paper Solved
• ICSE 2013 Physics Question Paper Solved
• ICSE 2012 Physics Question Paper Solved
• ICSE 2011 Physics Question Paper Solved
• ICSE 2010 Physics Question Paper Solved
• ICSE 2009 Physics Question Paper Solved
• ICSE 2008 Physics Question Paper Solved
• ICSE 2007 Physics Question Paper Solved

ICSE Physics Class 10 Previous Years Question Papers Are Prepared By Our Experts In Accordance With The Guidelines Given By ICSE Board. ICSE Physics Class 10 Solved Question Papers Will Help, Students Gain Confidence And Make Them Ready To Face Their ICSE Board Exams. ICSE Physics Class 10 Question Papers Cover Important Concepts From An Examination Perspective. ICSE Class 10 Physics Model Solutions Are Also Provided To Help Self-Evaluation.

We hope the ICSE Class 10 Physics Previous Years Question Papers Solved Last 10 Years Pdf Free Download with Solutions will help you. If you have any query regarding ICSE Class 10 Physics Solved Question Papers Last Ten Years with Answers, drop a comment below and we will get back to you at the earliest.

ICSE Previous Year Question Papers Class 10

APlusTopper.com provides ICSE Class 10 English Language Previous Year Board Question Papers Solved Pdf Free Download with Solutions, Answers and Marking Scheme. Here we have given ICSE Class 10 English Language Solved Question Papers Last Ten Years. Students can view or download the ICSE Board 10th English Language Previous Year Question Papers with Solutions for their upcoming examination.

These ICSE Class 10 English Language Previous 10 Years Board Question Papers with Answers are useful to understand the pattern of questions asked in the board exam. Know about the important concepts to be prepared for ICSE Class 10 Board Exam and Score More marks.

Board – Indian Certificate of Secondary Education (ICSE), www.cisce.org
Class – Class 10
Subject – English Language
Year of Examination – 2020, 2019, 2018, 2017.

ICSE Class 10 English Language Solved Question Papers Last Ten Years

ICSE Class 10 English Language Practice Papers With Answers Pdf

• ICSE English Language Question Paper 2019 Solved
• ICSE English Language Question Paper 2016 Solved
• ICSE English Language Question Paper 2015 Solved
• ICSE English Language Question Paper 2014 Solved
• ICSE English Language Question Paper 2013 Solved
• ICSE English Language Question Paper 2012 Solved
• ICSE English Language Question Paper 2011 Solved
• ICSE English Language Question Paper 2010 Solved
• ICSE English Language Question Paper 2009 Solved
• ICSE English Language Question Paper 2008 Solved
• ICSE English Language Question Paper 2007 Solved
• Letter Writing Topics ICSE Board Exams
• Informal Letter Writing
• Formal Letter Writing
• Essay Writing Topics
• Argumentative Essay Topics
• Descriptive Essay Topics
• Reflective Essay Topics

We hope the ICSE Class 10 English Language Previous Years Question Papers Solved Last 10 Years Pdf Free Download with Solutions will help you. If you have any query regarding ICSE Class 10 English Language Solved Question Papers Last Ten Years with Answers, drop a comment below and we will get back to you at the earliest.

ICSE Previous Year Question Papers Class 10

APlusTopper.com provides ICSE Class 10 Economics Previous Year Board Question Papers Solved Pdf Free Download with Solutions, Answers and Marking Scheme. Here we have given ICSE Class 10 Economics Solved Question Papers Last Ten Years. Students can view or download the ICSE Board 10th Economics Previous Year Question Papers with Solutions for their upcoming examination.

These ICSE Class 10 Economics Previous 10 Years Board Question Papers with Answers are useful to understand the pattern of questions asked in the board exam. Know about the important concepts to be prepared for ICSE Class 10 Board Exam and Score More marks.

Board – Indian Certificate of Secondary Education (ICSE), www.cisce.org
Class – Class 10
Subject – Economics
Year of Examination – 2020, 2019, 2018, 2017.

ICSE Class 10 Economics Solved Question Papers Last Ten Years

• ICSE Class 10 Economics Question Paper 2019 Solved
• ICSE Class 10 Economics Question Paper 2018 Solved
• ICSE Class 10 Economics Question Paper 2017 Solved
• ICSE Class 10 Economics Question Paper 2016 Solved
• ICSE Class 10 Economics Question Paper 2015 Solved
• ICSE Class 10 Economics Question Paper 2014 Solved
• ICSE Class 10 Economics Question Paper 2013 Solved
• ICSE Class 10 Economics Question Paper 2012 Solved
• ICSE Class 10 Economics Question Paper 2011 Solved
• ICSE Class 10 Economics Question Paper 2010 Solved
• ICSE Class 10 Economics Question Paper 2009 Solved

We hope the ICSE Class 10 Economics Previous Years Question Papers Solved Last 10 Years Pdf Free Download with Solutions will help you. If you have any query regarding ICSE Class 10 Economics Solved Question Papers Last Ten Years with Answers, drop a comment below and we will get back to you at the earliest.

ICSE Previous Year Question Papers Class 10

APlusTopper.com provides ICSE Class 10 Maths Previous Year Board Question Papers Solved Pdf Free Download with Solutions, Answers and Marking Scheme. Here we have given ICSE Class 10 Maths Solved Question Papers Last Ten Years. Students can view or download the ICSE Board 10th Maths Previous Year Question Papers with Solutions for their upcoming examination.

These ICSE Class 10 Maths Previous 10 Years Board Question Papers with Answers Solutions are useful to understand the pattern of questions asked in the board exam. Know about the important concepts to be prepared for ICSE Class 10 Board Exam and Score More marks.

ICSE Previous Year Question Papers Class 10 Maths With Solutions are solved last 10 years here.

Board – Indian Certificate of Secondary Education (ICSE), www.cisce.org
Class – Class 10
Subject – Maths
Year of Examination – 2020, 2019, 2018, 2017.

ICSE Class 10 Maths Solved Question Papers Last Ten Years

• ICSE 2019 Maths Question Paper Solved
• ICSE 2018 Maths Question Paper Solved
• ICSE 2017 Maths Question Paper Solved
• ICSE 2016 Maths Question Paper Solved
• ICSE 2015 Maths Question Paper Solved
• ICSE 2014 Maths Question Paper Solved
• ICSE 2013 Maths Question Paper Solved
• ICSE 2012 Maths Question Paper Solved
• ICSE 2011 Maths Question Paper Solved
• ICSE 2010 Maths Question Paper Solved
• ICSE 2009 Maths Question Paper Solved
• ICSE 2008 Maths Question Paper Solved
• ICSE 2007 Maths Question Paper Solved

We hope the ICSE Class 10 Maths Previous Years Question Papers Solved Last 10 Years Pdf Free Download with Solutions will help you. If you have any query regarding ICSE Class 10 Maths Solved Question Papers Last Ten Years with Answers, drop a comment below and we will get back to you at the earliest.

APlusTopper.com provides ICSE Class 10 Geography Previous Year Board Question Papers Solved Pdf Free Download with Solutions, Answers and Marking Scheme. Here we have given ICSE Class 10 Geography Solved Question Papers Last Ten Years. Students can view or download the ICSE Board 10th Geography Previous Year Question Papers with Solutions for their upcoming examination.

These ICSE Class 10 Geography Previous 10 Years Board Question Papers with Answers are useful to understand the pattern of questions asked in the board exam. Know about the important concepts to be prepared for ICSE Class 10 Board Exam and Score More marks.

Board – Indian Certificate of Secondary Education (ICSE), www.cisce.org
Class – Class 10
Subject – Geography
Year of Examination – 2020, 2019, 2018, 2017.

ICSE Class 10 Geography Solved Question Papers Last Ten Years

• ICSE 2019 Geography Question Paper Solved
• ICSE 2018 Geography Question Paper Solved
• ICSE 2017 Geography Question Paper Solved
• ICSE 2016 Geography Question Paper Solved
• ICSE 2015 Geography Question Paper Solved
• ICSE 2014 Geography Question Paper Solved
• ICSE 2013 Geography Question Paper Solved
• ICSE 2012 Geography Question Paper Solved
• ICSE 2011 Geography Question Paper Solved
• ICSE 2010 Geography Question Paper Solved
• ICSE 2009 Geography Question Paper Solved
• ICSE 2008 Geography Question Paper Solved
• ICSE 2007 Geography Question Paper Solved

We hope the ICSE Class 10 Geography Previous Years Question Papers Solved Last 10 Years Pdf Free Download with Solutions will help you. If you have any query regarding ICSE Class 10 Geography Solved Question Papers Last Ten Years with Answers, drop a comment below and we will get back to you at the earliest.

ICSE Previous Year Question Papers Class 10

APlusTopper.com provides ICSE Class 10 Biology Previous Year Board Question Papers Solved Pdf Free Download with Solutions, Answers and Marking Scheme. Here we have given ICSE Class 10 Biology Solved Question Papers Last Ten Years. Students can view or download the ICSE Board 10th Biology Previous Year Question Papers with Solutions for their upcoming examination.

These ICSE Class 10 Biology Previous 10 Years Board Question Papers with Answers are useful to understand the pattern of questions asked in the board exam. Know about the important concepts to be prepared for ICSE Class 10 Board Exam and Score More marks.

Board – Indian Certificate of Secondary Education (ICSE), www.cisce.org
Class – Class 10
Subject – Biology
Year of Examination – 2020, 2019, 2018, 2017.

ICSE Class 10 Biology Solved Question Papers Last Ten Years

ICSE Biology Class 10 Solved Question Papers

• ICSE 2019 Biology Question Paper Solved
• ICSE 2018 Biology Question Paper Solved
• ICSE 2017 Biology Question Paper Solved
• ICSE 2016 Biology Question Paper Solved
• ICSE 2015 Biology Question Paper Solved
• ICSE 2014 Biology Question Paper Solved
• ICSE 2013 Biology Question Paper Solved
• ICSE 2012 Biology Question Paper Solved
• ICSE 2011 Biology Question Paper Solved
• ICSE 2010 Biology Question Paper Solved
• ICSE 2009 Biology Question Paper Solved
• ICSE 2008 Biology Question Paper Solved
• ICSE 2007 Biology Question Paper Solved

We hope the ICSE Class 10 Biology Previous Years Question Papers Solved Last 10 Years Pdf Free Download with Solutions will help you. If you have any query regarding ICSE Class 10 Biology Solved Question Papers Last Ten Years with Answers, drop a comment below and we will get back to you at the earliest.

ICSE Previous Year Question Papers Class 10

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.

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.

(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:

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

(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.

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:

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.

Answer:

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.

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.

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

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:

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:

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.

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.

(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.

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

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:

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:

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 (O^2-)
Valency of O^2- = 2
(c) Aluminium nitride — (Al N)
Here valency of aluminium = 3
Another radical = Nitride (N^3-)
Valency of nitride (N^3-) = 3
(d) Aluminium sulphate — Al₂(SO₄)₃
Here valency of aluminium is 3
Another radical = Sulphate (SO₄^2-)
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).

Metal	Radicals	Valency
Iron	Ferrous [Iron (II)] Ferric [Iron (III)]	2 3
Copper	Cuprous [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.

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.

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:

Answer:

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