NCERT SOLUTION-CH-1-CHEMICAL REACTION & EQUATION || Class 10 Science Ch 1 Chemical Reactions And Equations question-answer.

NCERT Solution For Class 10 Science Chapter 1 Chemical Reactions And Equations.

Class 10 Science Chapter 1 Chemical Reactions And Equations exercise solution.

Chemical Reactions and Equations – Class 10 Science Question-Answer.

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NCERT TEXTBOOK QUESTION SOLVED

INTEXT QUESTIONS

Pg No. :- 6

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

Ans:-Because Magnesium is a very reactive element. It easily reacts with atmospheric oxygen to form a layer of magnesium oxide (MgO) which is very stable. To prevent further reaction of magnesium with oxygen it is necessary to clean magnesium ribbon for removing magnesium oxide(MgO) before burning in air. 

Q2. Write the balanced equation for the following chemical reactions :

(1)  Hydrogen + Chlorine →Hydrogen chloride

Ans.  H₂ + Cl → 2HCI

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

Ans .3BaCl₂ + Al₂ (S0₄) ₃ → 3BaSO₄ + 2AICI₃

iii) Sodium + Water Sodium→ hydroxide+ Hydrogen

Ans. 2Na + 2H₂0 → 2NaOH + H₂

Q3. 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.

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

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

Ans.  NaOH(aq) + HCl(aq)→ NaCl(aq) +H₂O (l)

Pg No. :- 10

 

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) The substance X is calcium oxide (quick lime). Its formula is Cao.

Q-2). Why is the amount of gas collected in one of the test tubes in Activity 1.7 double of the amount collected in the other? Name this gas.

Ans: - The gas is hydrogen.

During electrolysis, A balanced chemical equation shows that the water decomposes to form hydrogen and oxygen in the ratio of 2: 1 by volume.

the amount of hydrogen gas produced is double the amount of oxygen produced.

Pg No.:- 13

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

Ans. Because iron is more reactive than copper displaced copper from copper sulphate solution and iron sulphate is formed which is green in colour.

Q. 2. Give an example of a double displacement reaction other than the one was given in Activity 1.10

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

      (1)  4Na(s) + O2(g) → 2Na20(s)

(ii) CuO (s) + H2(g) → Cu (s) + H2O(1)

Answer:

 (i) Sodium(Na) is oxidised to Sodium oxide (Na₂O) and oxygen  is reduced.

 (ii) Hydrogen(H₂) is oxidised to Water(H₂O) and Copper(II) oxide(CuO) is reduced to copper (Cu).

 

NCERT TEXT-BOOK EXERCISE (Pg NO. 14-16)

 Q. 4 What is a balanced chemical equation? Why should chemical equations be balanced?

Ans: A balanced chemical equation has an equal number of atoms of different elements on both side of the equation (Reactant and Product side). 

3Fe (s) + 4H₂0 (g) ____ Fe304 (s) +4H₂(g)

The chemical equations should be balanced to satisfy the law of conservation of mass.

5. Translate the following statements into chemical equations and then balance them.

6. Balance the following chemical equations.

7. Write the balanced chemical equations for the following reactions.

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

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

Ans:- Exothermic Reactions:- Reaction in which heat or energy is released/evolved along with the formation of products.

e.g.  

 (1) Burning of natural gas

CH₄ (g) +0₂(g)→ CO₂(g) + 2H₂0 (g) + Heat

ii) Respiration is also an exothermic reaction.

C₆H₁₂O₆(aq) + 60₂ (g) →6C0₂ (aq) + 6H₂0 (l) + energy.

Endothermic Reactions: The reactions which require energy in the form of heat or light to break reactants  are called endothermic reactions.

e.g. 

N2 (g) + O2(g)    →     2NO     - Heat

C(s) + H2O (l)   →   CO(g) +H2(g)   -Heat

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

Ans: Respiration is an exothermic process because during respiration glucose combines with oxygen in the cells of our body to form carbon dioxide and water along with the production of energy.

11) Why are decomposition reactions called the opposite of combination reactions? Write equations for these reactions.

Ans:- DECOMPOSITION REACTION:- The reaction in which a single compound splits into two or more simple substances are called decomposition reaction.
eg;

CaCo3(s)  →CaO(s) + CO2(g)

COMBINATION REACTION: The reaction in which two or more reactant combine to form a single product.

CaO(s) + CO2(g)→CaCo3(s) 

That's why decomposition reactions called the opposite of combination reactions.

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

Ans:- Decomposition reaction involving absorption of heat, light or electricity

 
 

13. What is the difference between displacement and double displacement reactions? Write equations for these reactions. 

Ans: In displacement reactions, a more reactive metal displaces a less reactive metal from its solution.

 eg.

Fe(s) + CuSO4(aq) + Cu(s) + FeSO4(aq)

In this reaction, iron displaces copper from its solution.

→ In double displacement reactions, two reactants in solution exchange their ions.

eg. AgNO3(aq) + NaCl (aq) → AgCl(s) + NaNO3(aq)

In this reaction  silver nitrate and sodium chloride exchange  their ions.

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

Ans:-

2AgNO3 (aq) + Cu(s) → Cu(NO3)2 (aq) + 2Ag (s)

 Silver Nitrate + Copper → Copper Nitrate + Silver

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

Answer:- A reaction in which an insoluble solid called precipitate is formed that separates from the solution is called a precipitation reaction. 

Example:

Q-16,  Explain the following in terms of gain or loss of oxygen with two examples each:

 (a) Oxidation and (b) Reduction.

Answer: - (a) Oxidation:-

(i)The addition of oxygen to substance       OR

(ii) The removal of hydrogen from a substance. 

 

 

 (b) Reduction :-

(i) The addition of hydrogen to substance     OR

 (ii) The removal of oxygen from a substance.

Q.17 A shiny brown coloured element X' on heating in air becomes black in colour. Name the element X' and the black coloured compound formed.

Answer: Element "X" is copper (Cu). The black coloured compound is copper(II) oxide (CuO).

The reaction involved is:-

Q. 18. Why do we apply paint in iron articles?

Ans. Paint forms a protective layer on the surface of iron. It protect iron article from direct contact with air and water and saves iron from damage due to rusting.

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

Ans. Because of nitrogen act as an antioxidant and prevent oil and fat-containing food from getting oxidised.

20. Explain the following items with one example each :
(a) Corrosion  (b) Rancidity

a)  Corrosion:- The Process of Slow and gradual Conversion of metals into their undesirable compounds due to their reaction with air, moisture(water) present in the atmosphere is called Corrosion.

Eg. Rusting of Iron

Rusting:- Iron when reacts with oxygen and moisture forms the red substance which is called Rust.

4Fe(s) + 30₂(g) + H₂0 (l) — 2Fe₂O₃. xH₂0 (s)

Hydrated Ferric oxide (Rust)

The rusting of iron is a redox reaction.

Corrosion (rusting) weakens the iron and steel objects and structures such as railings, car bodies, bridges and ships etc. and cuts short their life.

 Methods to Prevent Rusting:-

 • By  painting. 

• greasing and oiling. 

• galvanization.

• electroplating.

b) Rancidity:- The oxidation of fats and oils when exposed to air is known as rancidity. It leads to bad smell and bad taste of food.

 Rancidity spoils the food materials prepared in fats and oils which have been kept for

considerable time and makes them unfit for eating.

Methods to prevent rancidity:

(i) By adding antioxidants 
(ii) Keeping food in airtight containers
(iii) Replacing air by nitrogen
(iv) Refrigerator

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