Chapter 5 – Language of Chemistry

Selina Concise Chemistry 2023 solutions for class 7 Chemistry. Chapter 5 – Language of Chemistry is provided here with simple step-by-step explanations. These solutions for Language of Chemistry (5th Chapter) are extremely popular among class 10 students. The Language of Chemistry solution is handy for quickly completing your homework and preparing for exams.

Book Name	: Concise Chemistry Middle School
Subject	: Chemistry
Class	: 7
Publisher	: Selina Publisher PVT Ltd
Chapter Name	: Language of Chemistry

EXERCISE

Question 1

1. Define chemical reaction.
2. What is a chemical equation?
3. Why do we need to balance chemical equations?

Answer

1. Chemical reaction: Any chemical change in a matter which involves its transformation into one or more new substances is called a chemical reaction.
2. Chemical equation: A chemical equation is the symbolic representation of a chemical reaction using the symbols and the formula of the substances involved in the reaction.
3. 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.

Question 2

State four conditions necessary for chemical reactions to take place.

Answer

Conditions necessary for chemical reactions :

1. Close contact
2. Solution form
3. Heat
4. Light
5. Catalyst

Question 3

Differentiate between :

1. Reactants and products.
2. Chemical reaction and chemical equation.
3. A balanced and a skeletal chemical equation.

Answer

(a) Reactants and products.

Reactants	Products
Starting materials that participate in a chemical reaction	Substances that are formed as a result of the chemical reaction
Participate in the chemical reaction	Are formed during the chemical reaction
Reactants are consumed during the chemical reaction	Products are generated as a result of the chemical reaction

(b) Chemical reaction and chemical equation.

Chemical Reaction	Chemical Equation
A process in which one or more substances are transformed into one or more different substances through the breaking and forming of bonds.	A symbolic representation of a chemical reaction that uses chemical formulas and symbols to represent the reactants and products involved.
Describes the chemical transformation that occurs.	Provides a concise representation of the reaction using chemical formulas and symbols.
Includes the reactants, products, and any intermediates or catalysts involved in the chemical transformation.	Includes the chemical formulas and symbols for the reactants and products, along with any coefficients or other symbols used to balance the equation.

(c) A balanced and a skeletal chemical equation

Balanced Chemical Equation	Skeletal Chemical Equation
The number of atoms of each element is the same on both sides	Only chemical formulas and symbols
Accurately represent reaction	Quick representation of the reaction
Chemical formulas and coefficients	Chemical formulas and symbols
Allows stoichiometric calculations and predictions	Provides a useful starting point for balancing
Examples – 2H2 + O2 → 2H2O	Examples – H2 + O2 → H2O

Question 4

Write word equations for the following skeletal equations:

1. KClO₃ → KCl + O₂
2. Zn + HCl → ZnCl₂ + H₂
3. FeCl₂ + Cl₂ → FeCl₃
4. CO + O₂ → CO₂
5. Ca + O₂ → CaO
6. Na + O₂ → Na₂O
7. NaOH + H₂SO₄ → Na₂SO₄ + H₂O
8. AgBr → Ag + Br₂
9. KNO₂ → KNO₂ + O₂

Answer

1. Potassium chlorate decomposes to form potassium chloride and oxygen gas.
2. Zinc reacts with hydrochloric acid to form zinc chloride and hydrogen gas.
3. Iron(II) chloride reacts with chlorine gas to form iron(III) chloride.
4. Carbon monoxide reacts with oxygen gas to form carbon dioxide.
5. Calcium reacts with oxygen gas to form calcium oxide.
6. Sodium reacts with oxygen gas to form sodium oxide.
7. Sodium hydroxide reacts with sulfuric acid to form sodium sulfate and water.
8. Silver bromide decomposes to form silver metal and bromine gas.
9. Potassium nitrite decomposes to form potassium nitrate and oxygen gas.

Question 5

Balance the following chemical equations :

1. FeS + HCl → FeCl₂ + H₂S
2. Na₂CO₃ + HCl → NaCI + H₂O + CO₂
3. H₂ + O₂ → H₂O
4. Na₂O + H₂O → NaOH

Answer

1. FeS + 2HCl → FeCl₂ + H₂S
2. Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂
3. 2H₂+ O₂ → 2H₂O
4. Na₂O + H₂O → 2NaOH

Question 6

What information do you get from the equation H₂+ Cl₂ → 2HCl?

Answer

1. Hydrogen and chlorine molecules are the reactants.
2. They are in gaseous form.
3. The product is hydrogen chloride gas.
4. Two molecules of hydrogen chloride are formed.

Question 7

Write your observations for the following chemical reactions and name the products formed :

1. When sugar is heated.
2. When manganese dioxide is added to potassium chlorate and heated.
3. When dilute acetic acid is poured on baking soda.
4. When an aqueous solution of sodium chloride is mixed with an aqueous solution of silver nitrate.
5. When ammonium chloride is heated with sodium hydroxide.
6. When water is added to quick lime?

Answer

1. A black solid mass (charcoal) is formed along with water vapours.
2. Manganese dioxide acts as a catalyst for the decomposition of potassium chlorate into potassium chloride and oxygen at a lower temperature.
3. Sodium acetate, CO₂ and water are formed.
4. A white insoluble solid precipitate of silver chloride is formed along with Sodium nitrate.
5. When solid ammonium chloride is heated with sodium hydroxide solution, gas ammonia is evolved which is recognised by its strong pungent smell.
6. When water is added to quick lime, a large amount of heat energy is evolved.

Question 8

Write symbolic representations for the following word equations and balance them :

1. Calcium carbonate → Calcium oxide + Carbon dioxide
2. Carbon + Oxygen → Carbon dioxide
3. Calcium oxide + Water → Calcium hydroxide
4. Aluminium + Chlorine → Aluminium chloride
5. Iron + Sulphur → Iron sulphide

Answer

1. CaCO₃ → CaO + CO₂
2. C + O₂ → CO₂
3. CaO + H₂O → Ca(OH)₂
4. 2Al + 3Cl₂ → 2AlCl₃
5. Fe + S → FeS

OBJECTIVE TYPE QUESTIONS

Question 1

Fill in the blanks:

1. The substances which undergo chemical change are called ____.
2. The substances formed as a result of a chemical reaction are called ____.
3. During a chemical reaction transfer of ____ takes place.
4. The basic condition necessary for a chemical reaction is ____.
5. In some chemical reactions, an insoluble ____ is formed when two solutions are mixed.

Answer

1. reactants
2. products
3. energy
4. close contact
5. precipitate

Question 2

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

1. No new substance is formed during a chemical reaction.
2. Hydrogen sulphide has a rotten egg smell.
3. When potassium iodide solution is added to lead acetate solution a red precipitate is formed.
4. A black residue is formed when sugar is heated.
5. When iron and sulphur are heated together a grey mass is formed which is attracted by a magnet.

Answer

1. False
2. True
3. False (it’s yellow)
4. True
5. True

MULTIPLE CHOICE QUESTIONS

Question 1

A chemical equation is a statement that describes a chemical change in terms of

1. symbols and formulae
2. energy
3. number of atoms
4. colours

Answer

symbols and formula

Explanation

A chemical equation is a statement that describes a chemical change in terms of symbols and formulae. It uses chemical formulas and symbols to represent the reactants and products involved in the reaction.

Question 2

Balancing a chemical equation is based on

1. Law of conservation of mass
2. Mass of reactants and products
3. Symbols and formulae
4. None of the above

Answer

Law of Conservation of Mass

Explanation

Balancing a chemical equation is based on the Law of Conservation of Mass. The law states that matter cannot be created or destroyed in a chemical reaction, and therefore the number of atoms of each element must be conserved in the reactants and products. Balancing the equation involves adjusting the coefficients of the chemical formulas to ensure that the number of atoms of each element is the same on both the reactant and product sides.

Question 3

Copper carbonate when heated, it turns :

1. Blue
2. Green
3. Black
4. Yellow

Answer

Black

Explanation

When copper carbonate is heated, it decomposes into copper oxide and carbon dioxide gas. The black colour observed is due to the formation of copper oxide, which has a black colour. The chemical reaction is given by:

CuCO₃ (s) → CuO(s) + CO₂ (g)

Question 4

When lead acetate solution is added to potassium iodide solution, a precipitate is formed which is

1. Red
2. Yellow
3. White
4. Black

Answer

yellow

Explanation

When lead acetate solution is added to potassium iodide solution, a precipitate is formed which is yellow. The yellow precipitate is lead iodide (PbI2), which is insoluble in water and forms a solid precipitate when the two solutions are mixed. The balanced chemical equation for the reaction is:

Pb(CH₃COO)₂ (aq) + 2KI (aq) → PbI₂ (s) + 2CH₃COOK (aq)

Question 5

This gas has a rotten egg smell

1. Ammonia
2. Hydrogen
3. Hydrogen sulphide
4. Oxygen

Answer

Hydrogen sulphide

Explanation

The gas that has a rotten egg smell is hydrogen sulphide (H₂S). It is a colourless, toxic, and flammable gas that is produced naturally in the environment by the decay of organic matter.

Question 6

When sodium carbonate reacts with dilute hydrochloric acid, the gas evolved is

1. carbon-dioxide
2. Nitrogen
3. Oxygen
4. Hydrogen

Answer

Carbon dioxide

Explanation

When sodium carbonate reacts with dilute hydrochloric acid, the gas evolved is carbon dioxide (CO₂). The chemical reaction between sodium carbonate and hydrochloric acid is given by the following equation:

Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂