CLASS 10 SCIENCE, S. CHAND TEXTBOOK QUESTIONS AND ANSWERS (11-20)

Very short answer type questions:

11) Write the balanced chemical equations for the following reactions:

a) Calcium hydroxide + Carbon dioxide          —->        Calcium carbonate + Water

Ans) Ca(OH)₂ + CO₂     —->    CaCO₃  + H₂O

b) Aluminium + Copper chloride          —->        Aluminium chloride + Copper

Ans) 2Al + 3 CuCl₂           —->          2AlCl₃ + 3Cu

12) Complete and balance the following equations:

a) NaOH + …………..        —->        Na₂SO₄ + H₂O

Ans) NaOH +   H₂SO₄             —->           Na₂SO₄ + H₂O

b) Ca(OH)₂ + ………….  —->   CaCO₃ + H₂O

Ans) Ca(OH)₂ + CO₂     —->    CaCO₃ + H₂O

13) Correct and balance the following equations:

a) Ca + H₂O       —->      CaOH + H

Ans) Ca + 2 H₂O       —->      Ca(OH)₂ + H₂

b) N + H       —->      NH₃

Ans) N₂ + 3H₂      —->     2 NH₃

14) Write complete balanced equations for the following reactions:

a) Calcium(solid) + water (liquid)          —->          Calcium hydroxide(solution) + Hydrogen(gas)

Ans)  Ca(s) + 2H₂O (l)     —->    Ca(OH)₂(aq) + H₂(g)

b) Sulphur dioxide (gas) + Oxygen (gas)           —->       Sulphur dioxide(gas)

Ans) 2SO₂ (g) + O₂ (g)      —-> 2SO₃(g)

15) Balance the following equations:

(i) Na + O₂      —->      Na₂O

Ans) 4Na + O₂            —->          2 Na₂O

(ii) H₂O₂          —->          H₂O + O₂

Ans) 2H₂O₂         —->        2H₂O + O₂

(iii) Mg(OH)₂ + HCl          —->        MgCl₂ + H₂O

Ans) Mg(OH)₂ + HCl             —->     MgCl₂ + H₂O

iv) Fe + O₂      —->     Fe₂O₃

Ans) 4Fe +3O₂    —->    2Fe₂O₃

v) Al(OH)₃     —->      Al₂O₃ + H₂O

Ans) 2 Al(OH)₃     —->     Al₂O₃ + 3H₂O

vi) NH₃ + CuO          —->         Cu + N₂ + H₂O

Ans) 2NH₃ + 3 CuO           —->        3Cu + N₂ + 3H₂O

vii)Al₂(SO4)₃ + NaOH       —->     Al(OH)₃ +Na₂SO₄

Ans) Al₂(SO4)₃ + 6NaOH       —->      2 Al(OH)₃ +3Na₂SO₄

viii)HNO₃ + Ca(OH)₂         —->        Ca(NO₃)₂ +H₂O

Ans) 2HNO₃ + Ca(OH)₂        —->      Ca(NO₃)₂ +2 H₂O

ix)NaOH + H₂SO₄                   —-> Na₂SO₄  + H₂O

Ans) 2NaOH + H₂SO₄        —->       Na₂SO₄  + 2 H₂O

x) BaCl₂ + H₂SO₄         —->       BaSO₄ + HCl

Ans) BaCl₂ + H₂SO₄         —->         BaSO₄ + 2HCl

16) Fill the following blanks with suitable words:

a) Chemical equations are balanced to satisfy the Law of Conservation of Mass

b) A solution made in water is known as an aqueous solution and indicated by the symbol (aq)

Short Answer Type Questions:

17) a) Give one example of a chemical reaction.

b) State two characteristics of the chemical reaction which takes place when dil sulphuric acid is poured over zinc granules

c) State two characteristics of the chemical reaction which occurs on adding potassium iodide solution to lead nitrate solution

Ans) a) Magnesium ribbon when heated in the presence of air, reacts with oxygen in the air to form a white powder called Magnesium oxide.

2Mg(s) + O₂(g)            —->        2MgO(s)

b) When dil sulphuric acid is poured over zinc granules

(i) There will be evolution of hydrogen gas

(ii) There will be a rise in the temperature as it is an exothermic reaction.

c) The two characteristics of the chemical reaction which occurs on adding potassium iodide solution to lead nitrate solution are

2KI + Pb(NO₃)₂       —->     2KNO₃ + PbI₂

(i) A precipitation reaction occurs in which a yellow precipitate is formed due to the formation of Lead iodide

(ii) There will be a change in colour (from colourless to yellow) also takes place in this chemical reaction.

18) a) What is a chemical reaction? Explain with the help of an example.

b) Giving examples, state the difference between balanced and unbalanced chemical equation

c) Balance the following chemical equations:

(i) NH₃       —->      N₂ + H₂

(ii) C + CO2        —->      CO

Ans) a) Chemical reactions are processes in which new substances with new properties are formed. The burning of magnesium in air to form magnesium oxide is an example of a chemical reaction.

Magnesium ribbon when heated in the presence of air reacts with oxygen in the air to form a white powder called Magnesium oxide.

2Mg(s) + O₂(g)           —->         2MgO(s)

The properties of the product (magnesium oxide) are entirely different from those of the reactants (Magnesium and oxygen)

b)

Balanced chemical equation	Unbalanced chemical equation
A balanced chemical equation has an equal number of atoms of different elements in the reactants and products.	An unbalanced chemical equation has unequal number of atoms of one or more elements in the reactants and products.
A balanced chemical equation has equal masses of various elements in reactants and products.	An unbalanced chemical equation has unequal masses of various elements in reactants and products.
Zn + H2SO4    —->   ZnSO4 + H2	H2 + O2   —->  H2O

c) Balance the following chemical equations:

(i) NH₃       —->      N₂ + H₂

Ans) 2NH₃      —->    N₂ + 3H₂

(ii)C + CO₂        —->        CO

Ans) C + CO₂      —->      2CO

19) When hydrogen is passed over copper oxide, copper and steam are formed. Write a balanced equation for this reaction and state which of the chemicals are

(i) elements   (ii) compounds   (iii) reactants    (iv) products   (v) metals   (vi) non-metals

Ans) H₂ + CuO         —->       Cu + H₂O

• elements  – H₂  and Cu
• Compounds- CuO and H₂O
• reactants –H₂ and CuO
• Products- Cu and H₂O
• Metal- Cu
•  Non-metal- H₂

20) a) What are the various ways in which a chemical equation can be made more informative? Give examples to illustrate your answers.

b) Write a balanced chemical equation from the following information:

An aqueous calcium hydroxide solution(lime water) reacts with carbon dioxide gas to produce a solid calcium carbonate precipitate and water.

Ans) The chemical equation can be made more informative in three ways-

• By indicating the “physical states” of the reactants and products.
• By indicating the “heat changes” taking place in the reaction
• By indicating the “conditions” under which the reaction takes place.

By indicating the “physical states” of the reactants and products.

Information regarding the physical states of the reactants and products, can be provided by using the letters(s), (l), (g) and (aq) for solid, liquid, gas and a solution in water (aqueous), respectively, at the end of the formula of the substance involved.

For example, solid sodium metal reacts with water atomic room temperature to produce hydrogen gas, and a solution of sodium hydroxide in water. Then , the complete chemical equation is..

• 2Na(s) + 2H₂O (l)     —->    2NaOH (aq) + H₂ (g)

By indicating the “heat changes” taking place in the reaction: There are two types of reactions on the basis of heat changes involved: Exothermic reactions and Endothermic reactions.

Chemical reactions takes place either with the evolution or absorption of heat. The reactions in which heat is given out are called exothermic reactions. This information is given by writing “+ heat” or “+ Heat energy” or just “+ energy” on the product-side (right hand side) of the chemical equation.

For example,

(a) When carbon is burnt in air (or oxygen) heat is evolved. Then, the chemical equation is written as,

C(s) + O₂ (g)         —->     CO₂ (g) + Heat

The reactions in which heat is absorbed from the surroundings are called endothermic reactions. This information is given by writing “+ heat” or “+ Heat energy” or just “+ energy” on the reactants-side (left hand side) of the chemical equation.

For example,

The information about the temperature, pressure conditions, and presence of catalyst etc. is given above the arrow (→) separating the reactants and products.

For example, 

The mixture of CO and hydrogen gas is compressed to 300 atmospheres pressure and then passed over a catalyst consisting of ZnO +CrO₃ heated to a temperature of 300⁰C

b) Write a balanced chemical equation from the following information:

An aqueous calcium hydroxide solution(lime water) reacts with carbon dioxide gas to produce a solid calcium carbonate precipitate and water.

Ans) Ca(OH)₂(aq) + CO₂(g)    —->    CaCO₃(s) + H₂O(l)