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NCERT Solutions for Class 10 Science Chapter 1 Chemical reactions and equations

NCERT Solutions for Class 10 Science Chapter 1 – Chemical reactions and equations is an outstanding study resource needed for the student studying in CBSE class 10. These NCERT Solutions are crafted as per the latest CBSE syllabus 2020-21 by subject experts.

CBSE Class 10 Science chapter 1 has good weightage and there will be around 4 questions being asked every year from this chapter. Type of questions that arise in this chapter is mostly of practice-based question. Thorough knowledge and good practice will help you score full marks on the questions asked in this chapter.

NCERT Solutions for Class 10 Science Chapter 1

Intext Questions

(A) QUESTIONS GIVEN ON PAGE NUMBER 6 OF THE TEXTBOOK

Q.1. Why should a magnesium ribbon be cleaned before burning in air?

Ans. This is done to remove the layers of magnesium oxide and magnesium carbonate from the surface of magnesium ribbon. These layers are formed as a result of reaction with atmospheric oxygen and carbon dioxide. Magnesium ribbon is cleaned by rubbing with sand-paper after which magnesium ribbon burns smoothly.

Q.2. Write the balanced equation for the following chemical reactions:

(i) Hydrogen + Chlorine → Hydrogen chloride

(ii) Barium chloride + Aluminium sulphate → Barium sulphate + Aluminium chloride

(iii) Sodium + Water → Sodium hydroxide + Hydrogen.

Ans. Balanced equations in the symbolic form are given as under:

(i) H2 + Cl2 → 2HCI

(ii) 3BaCl2 + Al2 (SO4)3 → 3BaSO4 + 2AlCl3

(iii) Na + 2H2O → 2NaOH + H2

Q.3. Write a balanced chemical equation with state symbols for the following reactions:

(i) Solutions of barium chloride and sodium sulphate in water react to give insoluble

barium sulphate and the solution of sodium chloride.

(ii) Sodium hydroxide solution (in water) reacts with hydrochloric acid solution (in water) to produce sodium chloride solution and water.

Ans. Balanced equations in symbols and formulae with state symbols for the above reactions are given as under

(i) BaCl2 (aq)+ Na2SO4 (aq) → BaSO4 (s) + 2NaCl (aq)

       Barium chloride       Sodium sulphate             Barium sulphate   Sodium chloride

(ii) NaOH (aq)+ HCl (aq) → NaCl (aq) + H2O (l)

       Sodium hydroxide   Hydrochloric acid      Sodium chloride      Water

[B] QUESTIONS GIVEN ON PAGE NUMBER 10 OF THE TEXTBOOK

Q.1. A solution of a substance X' is used for white washing.

(i) Name the substance X and write its formula.

(ii) Write the reaction of the substance X' named in (i) above with water.

Ans. (i) Substance 'X' used for white washing is calcium oxide (or quick lime). Its formula is CaO.

(ii) Calcium oxide reacts with water as under:

CaO (s) + H2O (l) → Ca(OH)2 (aq)

Calcium oxide     Water                Calcium hydroxide

Q.2. Why is the amount of gas collected in one of the test tubes in Activity 5 double of

the amount collected in the other ? Name this gas.

Ans. Electric current is passed through water acidulated with sulphuric acid. The gas collected over the cathode is hydrogen and the gas collected over anode is oxygen.

The volume of gas collected over cathode i.e., Hydogen gas is double the volume of gas collected over anode i.e., Oxygen gas.

This can be explained with the help of the chemical reaction that takes place

                        2H2O (l) → 2H2 (g) +O2 (g)

Volume of the gas is proportional to the number of molecules of the gas as indicated in the balanced equation. There are two molecules of hydrogen and one molecule of oxygen in the balanced equation. Hence, hydrogen collected has twice the volume of oxygen collected.

[C] Questions Given On Page Number 13 Of Textbook

  

Q.1. Why does the colour of copper sulphate solution change when an iron nail is dipped in it ?

Ans. Fe(s)  +  CuSO4(aq) -------->    FeSO4(aq)  +      Cu(s)

               Iron        Copper Sulphate                             Ferrous Sulphate               Copper

                               (blue colour).                                    (very light green)

Displacement reaction takes place. Copper is deposited and Ferrous sulphate solution is obtained which is very light green in colour compared to dark blue colour of copper sulphate. Hence a colour change is noticed.

Q.2. Give an example of a double displacement reaction other than the one given in Activity 8.

Ans. 

     Pb(NO3)2 (aq)  + 2KI (aq)  --------> PbI2(s) + 2KNO3(aq)

            Lead nitrate                Potassium iodide                   Lead iodide      Potassium nitrate

When we mix aqueous solutions of lead nitrate, Pb(NO3)2 and potassium iodide, KI, we obtain a precipitate of lead iodide and a solution of potassium nitrate. In this reaction, the cation,Pb2+ and K+ exchange their anions, NO3-  and I- to give the new substances  PbI2  and KNO3 .

Q.3. Identify the substances that are oxidised and the substances that are reduced in the following reactions :

i) 4Na(s) + O2(g) ------> 2Na2O(s)

ii) CuO(s) + H2(g) -------> Cu(s) + H2O(l)

Ans. i) 4Na(s) + O2 (g) ------->   2Na2O (s)

In this reaction, sodium is oxidised because it combines with oxygen to form sodium oxide.

ii) CuO(s)  +  H2(g) -------> Cu(s) + H2O(l)

In this reaction, CuO is reduced because it loses oxygen and H2 is oxidised because it combines with the oxygen of CuO to form water..

Exercise Questions

Qu.1  Which of the statements about the reaction below are incorrect.

a) Lead is getting reduced.

b) Carbon dioxide is getting oxidized. 

c) carbon is getting oxidized. 

d) Lead oxide is getting reduced.

Reason :- both (a) and (b) are incorrect because lead oxide is reduced not lead similarly carbon is getting oxidised not carbon dioxide in the above reaction.

Qu.2 

The above reaction is an example of a 

a) combination reaction

b) double displacement reaction 

c) decomposition reaction 

d) displacement reaction

Answer :-  d) displacement reaction.

Qu.3  What happens when dilute hydrochloric acid is added to iron fillings?  Tick the correct answer

a) Hydrogen gas and iron chloride are produced 

b) Chlorine gas and iron hydroxide are produced

c) No reaction taken place 

d) A Iron salt and water are produced.

Answer :- a) hydrogen gas and iron chloride are produced.

Qu.4  What is balanced chemical equation? Why should chemical equation be balanced?

Answer:- The chemical reaction in which the number of atoms of each elements remains the same before and after the reaction such reaction are known as balanced chemical reaction

chemical equation should be balanced because only a balanced equation tells us the relative quantities of different reactants and products involved in the reaction.

Qu.5 Translate the following statement into chemical equation and then balance them –

a) Hydrogen gas combines with nitrogen to form ammonia.

b) Hydroge sulphide gas burns in air to give water and sulphur dioxide.

c) Barium chloride react with aluminium sulphate to give aluminium chloride and a precipitate of Barium sulphate.

d) Potassiu metal react with water to give potassium hydroxide and hydrogen gas.

Answer :-

Qu.6  Balance the following chemical equations :-

Qu.7  Write the balanced chemical equation for the following reactions.

a) Calcium hydroxide + carbon dioxide ------> Calcium carbonate + water

b) Zin + Silver nitrate ------> Zinc nitrate + Silver

c) Aluminium + Copper chloride ------> Aluminium chloride + Copper

d) Barium chloride + Potassium sulphate -------> Barium sulphate + Potassium  chloride

Qu.8  Write the balanced chemical equation for the following and identify the type of reaction in each case.

a) Potassium bromide (aq.)  + Barium iodide (aq.) -------> Potassium iodide (aq.) + Barium bromide(aq.)

b) Zinc carbonate ------> Zinc oxide + carbon dioxide

c) Hydrogen(g) + Chloride(g) -----> Hydrogen chloride

d) Magnesium (s) + Hydrochloric acid (aq.) ------> Magnesium chloride + hydrogen.

Answer :-

Qu.9  What does one mean by exothermic and endothermic reaction? Give Examples.

Answer:-  

Exothermic:- The  reactions in which energy is released in the form of light and heat are   called Exothermic reactions.

Endothermic reaction :-  The  reactions in which energy is absorbed from the surroundings and is produced are called Endothermic reactions.

Qu.10  Why is respiration considered an exothermic reaction? Explain.

Answer :- During Respiration we inhale oxygen from the atmosphere which reacts with glucose in our body to produce carbon dioxide and water.

Heat is liberated in this process, hence respiration is considered an exothermic reaction.

Qu.11  Why are decomposition reactions called the opposite of combination reaction? write equation for these reactions.

Answer :-

In decomposition reaction a single reactants  decomposes into two or more substances where as in combination reaction two or more reactants combine to form a single product therefore decomposition reactions called the opposite of combination reaction.

Qu.12  Write one equation each for decomposition reaction where energy supplied in the form of heat,light or electricity.

Answer :-

Qu.13  What is the difference between displacement and double displacement reaction? Write the equation for these reactions.

Answer :-

Displacement reaction:- The reaction in which an element displaces another element from its compound are called displacement reaction.

Double displacement reaction :- The reaction in which an exchange of ions occurs between the reactants are called double displacement reaction.

Qu.14  In the refining of silver, the recovery of silver from silver nitrate solution involved displacement by copper metal. Write down the reaction involved.

Answer :-

Qu.15  What do you mean by a precipitate reaction? Explain by giving examples.

Answer :- The reaction in which a precipitate(insoluble substance) is formed as a product are called precipitation reaction.

Qu.16  Explain the following terms of gain or loss of oxygen with two examples of each.

a. Oxidation

b. Reduction 

Answer :-

a. Oxidation :- Addition of oxygen or removal of hydrogen in a reaction is called oxidation.

b. Reduction :- Addition of hydrogen or removal of oxygen in a reaction is called reduction.

Qu.17  A Shiny a brown coloured element X on heating in air becomes black in colour name the element X and the black coloured compound formed.

Answer :-

The Shiny brown colour element X is copper. On heating in air it forms copper oxide which is black in colour.

Qu.18  Why do we apply paint on iron articles?

Answer :-

We apply paint on an iron articles to prevent rusting (corrosion). Iron articles to not come into contact with atmospheric oxygen and moisture and thus rusting is prevented.

Qu.19  Oil and fat containing food items are flushed with nitrogen. Why?

Answer :-

Oil and fat containing items get rancid due to oxidation with atmospheric oxygen. To prevent that that such items are flushed with nitrogen. Nitrogen does not react with oil and fat containing articles.

Qu.20   Explain the following terms with one example each :- 

a. Corrosion

b. Rancidity

Answer :-

a. Corrosion :- Metals are attacked by atmospheric oxygen,carbon dioxide and moisture and are converted into metal oxide and carbonates This phenomenon is called corrosion. In the case of iron corrosion is called rusting.

Example :-  Green coating on copper and black coating on silver are examples of corrosion  

b. Rancidity :- The phenomena of reaction of atmospheric oxygen with oils and fats is called rancidity. Rancidity can be prevented by flushing oil and fat containing articles with nitrogen.

Example :- When fats and oils containing articles kept for sometime in the open, start giving bad smell and taste.