Living Science Chemistry Class 8 ICSE Solutions Chapter 5 Language of Chemistry

ICSE Living Science Chemistry for Class 8 Solutions Chapter 5 Language of Chemistry

Think And Answer (Page 57)

Can all chemical changes be represented by chemical equations?
Answer:
Yes, all chemical changes be represented by chemical equations.

Check Your Progress (Page 60)

Answer these questions.
Question 1.
Write skeletal equations for the following word equations.
a. magnesium + oxygen → magnesium oxide
b. hydrogen + chlorine → hydrogen chloride
c. calcium carbonate → calcium oxide + carbon dioxide
d. zinc carbonate → zinc oxide + carbon dioxide
Answer:
a. Mg + O₂ → MgO
b. H₂ + Cl₂ → HCl
c. CaCO₃ → CaO + CO₂
d. ZnCO₃ → ZnO + CO₂

Question 2.
Balance the following equations.
a. Ca + O₂ → CaO
b. HgO → Hg + O₂
c. Fe + O₂ → Fe₂O₃
d. N₂ + H₂ → NH₃
Answer:
a. 2Ca + O₂ → 2CaO
b. 2HgO → 2Hg + O₂
c. 2Fe + 3O₂ → Fe₂O₂
d. N₂ + 3H₂ → 2NH₃

A. Tick the most appropriate answer

Question 1.
Which of the following has variable valencies?
a. sodium
b. calcium
c. copper
d. chlorine
Answer:
c. copper

Question 2.
Which of the following is a potassium ion?
a. K³⁺
b. K²⁺
c. K⁺
d. K
Answer:
c. K⁺

Question 3.
Which of the following is a nirite ion?
a. NO₂^–
b. NO₃^–
c. NO^–
d. NO₂
Answer:
a. NO₂^–

Question 4.
What is the chemical formula of ammonia?
a. NH₂
b. NH
c. N₂H
d. NH₃
Answer:
d. NH₃

Question 5.
What is the product of the following reaction?
C + O₂ → CO₂
a. C
b. O₂
c. CO₂
d. all of these
Answer:
c. CO₂

Question 6.
What is the coefficient of MgO in the following reaction?
Mg + O₂ → 2MgO
a. 1
b. 2
c. 3
d. 0
Answer:
b. 2

B. Fill in the blanks

Question 1.
The ………………. of an element is the one- or two-letter abbreviation of its name.
Answer:
The symbol of an element is the one- or two-letter abbreviation of its name.

Question 2.
An atom that loses one or more electrons to form a positive ion is called a ……………….
Answer:
An atom that loses one or more electrons to form a positive ion is called a cation.

Question 3.
The ………………. of a compound is the symbolic representation of its composition.
Answer:
The chemical formula of a compound is the symbolic represen-tation of its composition.

Question 4.
The representation of a chemical reaction by using the symbols and formulae of the reactants and the products involved in the reaction is called its chemical ……………….
Answer:
The representation of a chemical reaction by using the symbols and formulae of the reactants and the products involved in the reaction is called its chemical equation.

Question 5.
If the number of atoms of each element on both the sides of a chemical equation is equal, then the equation is called a ………………. chemical equation.
Answer:
If the number of atoms of each element on both the sides of a chemical equation is equal, then the equation is called a balanced chemical equation.

Question 6.
A ………………. is a number that we place in front of a symbol or formula in an equation.
Answer:
A coefficient is a number that we place in front of a symbol or formula in an equation.

Question 7.
………………. is neither created nor destroyed during a chemical reaction.
Answer:
Matter is neither created nor destroyed during a chemical reaction.

C. Write true or false. Correct the false statements

Question 1.
Iron has only one valency.
Answer:
False; Iron exhibit variable valencies.

Question 2.
When an atom loses or gains electrons, it becomes a charged particle.
Answer:
True

Question 3.
An atom that gains one or more electrons to form a negative ion is called a cation.
Answer:
False; An atom that gains one or more electrons to form a negative ion is called a anion.

Question 4.
A hydroxide ion is a polyatomic ion.
Answer:
True

Question 5.
The chemical formulae of different compounds can be written easily if the symbols and the valencies of the elements are known.
Answer:
True

Question 6.
The law of conservation of mass states that mass is created during a chemical reaction.
Answer:
False; The law of conservation of mass states that mass is neither created nor destroyed during a chemical reaction.

Question 7.
If heat is evolved during the reaction, it is endothermic.
Answer:
False; If heat is evolved during the reaction, it is exothermic.

D. Match the columns

1. Positively charged ion	a. sulphite ion
2. ZnS	b. anion
3. Valency	c. catalyst
4. MnO2	d. zinc sulphide
5. S–	e. cation
	f. whole number

Answer:

1. Positively charged	e. cation
2. ZnS	d. zinc sulphide
3. Valency	f. whole number
4. MnO2	c. catalyst
5. S–	a. sulphite ion

E. Write the formulae for the following
1. Aluminium chloride
2. Magnesium hydroxide
3. Calcium chloride
4. Sodium carbonate
5. Copper (II) oxide
6. Iron(II) sulphide
Answer:
1. Aluminium chloride – AlCl₃
2. Magnesium hydroxide – Mg (OH)₂
3. Calcium chloride – CaCl₂
4. Sodium carbonate – Na₂ CO₃
5. Copper (II) oxide – CuO
6. Iron(II) sulphide – FeS

F. Write the names of the compounds represented by the following formulae

1. Al₂(SO₄)₃
2. K₂SO₄
3. KNQ₃
4. CaCO₃
5. MgCl₂
Answer:
1. Al₂ (SO₄)₃ – aluminium sulphate
2. K₂SO₄ – potassium sulphate
3. KNO₃ – potassium nitrate
4. CaCO₃– calcium nitrate
5. MgCl₂ – magnesium chloride

G Define the following terms

Question 1.
Symbol
Answer:
The symbol of an element is the one- or two – letter abbreviation of its name.

Question 2.
Valency
Answer:
Valency is the number of electrons an atom can donate or accept to form a chemical bond with another atom. It is the combining capacity of an atom of an element.

Question 3.
Ion
Answer;
Ion is an atom or group of atoms that has lost or gained one or more electrons, making it positively or negatively charged.

Question 4.
Cation
Answer:
An atom that loses one or more electrons to form a positive ion is called a cation.

Question 5.
Anion
Answer:
An atom that gains one or more electrons to form a negative ion is called an anion.

H. Write chemical equations in symbols and formulae for the following word equations

Question 1.
iron + sulphur → iron(II) sulphide
Answer:
Fe + S → FeS

Question 2.
magnesium + oxygen → magnesium oxide
Answer:
2Mg + O₂ → 2MgO

Question 3.
calcium carbonate -» calcium oxide + carbon dioxide
Answer:
CaCO₃ → CaO + CO₂

Question 4.
silver chloride -» silver + chlorine
Answer:
2AgCl → 2Ag + Cl₂

I. Answer the following in short

Question 1.
How is a cation formed?
Answer:
An atom that loses one or more electrons to form a positive ion is called a cation.

Question 2.
How is an anion formed?
Answer:
An atom that gains one or more electrons to form a negative ion is called an anion.

Question 3.
What is a polyatomic ion?
Answer:
An ion that consists of a group of atoms with an overall charge is called a polyatomic or compound ion.

Question 4.
Name the polyatomic ion that carries a positive charge.
Answer:
Ammonium ion (NH⁺₄)

Question 5.
What is a chemical formula?
Answer:
The chemical formula of a compound is the symbolic representation of its composition. It tells the number of atoms of various elements present in one molecule of a compound.

Question 6.
Differentiate between a balanced chemical equation and an unbalanced chemical equation.
Answer:
If the number of atoms of each element on both the sides of the chemical equation is equal, then the equation is called a balanced chemical equation. If the number of atoms of each element on both sides of the chemical equation is not equal, then the chemical
equation is called an unbalanced chemical equation. It is also known as a skeletal equation.

Question 7.
What is the law of conservation of mass?
Answer:
The law of conservation of mass states that matter is neither created nor destroyed during a chemical reaction.

Question 8.
Write the symbols for all physical states.
Answer:
The symbols for the physical state of reactants and products are:
(s) for solid state
(l) for liquid state
(g) for gaseous state
(aq) for aqueous solution

J. Answer the following in detail

Question 1.
Write the difference between monoatomic ions and polya tomic ions with the help of examples.
Answer:
An ion that consists of only a single atom with a charge is called a simple ¡on or monoatomic ion. For example, a sodium ion
(Na₂) is a simple ion. An ion that consists of a group of atoms with an overall charge is called a polyatomic or compound ion. For example, an ammonium ion (NH⁺₄) is a polyatomic ion.

Question 2.
What are the rules for writing the formulae of compounds?
Answer:
Rules for writing the formulae of compounds The following are the rules for writing the formulae of compounds.

• Write the symbols of the elements or ions that form the compound.
• Wnte the valency of each element or the charge of each ion below its symbol.
• Finally, interchange the valencies or charges of the combining atoms or ions and write them as subscripts.
• if the valencies or charges are divisible by a common factor, divide and simplity the formula.
• For charges, exclude the + and – signs, exchange the numbers, and then write them as subscripts.

Question 3.
Describe a chemical equation with an example.
Answer:
A chemical reaction is represented by a chemical equation. There are two ways of representing a chemical equation.
1. In words (called a word equation): For example, the reaction of carbon with oxygen to produce carbon dioxide can be written in words as: Carbon + oxygen → carbon dioxide

2. In symbols and formulae: The above reaction can be written in symbols and formulae as:
C + O₂ → CO₂
Carbon oxygen carbon dioxide

The substances that react with one another in a reaction are called reactants and the new substances produced by the reaction are called products. In the above reaction, carbon and oxygen are the reactants and carbon dioxide is the product.

Question 4.
Write about the limitations of a chemical equation.
Answer:
Limitations of a chemical equation :
A chemical equation does not give information about the following,

1. The physical state of the reactants and products of a reaction
2. The concentration of the reactant of a reaction. If an acid is one of the reactants, it may be dilute or concentrated.
3. The nature of a reaction. If heat is evolved during the reaction, it is exothermic. If heat is absorbed during the reaction, it is endothermic.
4. The conditions of a reaction. A chemical equation does not give any information about the pressure, temperature, concentration, pressure of catalyst, etc under which the reaction occurs.
5. The direction of a reaction. Certain chemical reactions can proceed in both the forward and backward directions. The reactants change into the forward reaction. The products , can be converted into the reactants in the backward reaction. Such reactions are also called reversible reactions.

K. Balance the following equations
1. Na + H₂O → NaOH + H₂
2. N₂ + O₂ → NO
3. KClO₂ → KCl + O₂
4. NO + O₂ → NO,
Answer:
1. 2Na + 2H₂O → 2NaOH + H2
2. N₂ + O₂ → 2NO
3. 2KClO₃ → 2KCl + 3O₂
4. 2NO + O₂ → 2NO₂

Living Science Chemistry Class 8 ICSE Solutions