Chemical Reactions and Equations NCERT Solution, study material, CBSE Notes

NCERT Solution: Chemical Reactions and Equations

Give the characteristic tests for the following gases

(a) CO₂
Ans. When carbon dioxide is passed into lime water, the lime water turns milky. This is the characteristic test for carbon dioxide.
(b) SO₂

Ans. Sulphur dioxide smells like rotten egg.
(c) O₂
Ans. When a burning matchstick is brought near oxygen, the matchstick burns even more brightly. This is the characteristic test for oxygen.
(d) H₂
Ans. When a burning matchstick is brought near hydrogen gas, the matchstick burns with a pop sound

What happens when a piece of

(a) zinc metal is added to copper sulphate solution?
Ans. Zinc displaces copper to form zinc sulphate.
Zn(s) + CuSO₄(aq) → ZnSO₄(aq) +Cu

(b) aluminium metal is added to dilute hydrochloric acid?
Ans. Aluminium reacts with dil.hydrochloric acid to form aluminium chloride. Hydrogen gas is evolved in this rection.

2Al(s) + 6HCl(aq) → AlCl₃(aq) + 3H₂

(c) silver metal is added to copper sulphate solution?
Ans. Silver is less reactive than copper. Hence, no reaction takes place.

What happens when zinc granules are treated with dilute solution of H₂SO₄ , HCl, HNO₃, NaCl and NaOH, also write the chemical equations if reaction occurs

The reaction of Zn granules with
(a) Dilute H₂SO₄

Zn(s) +H₂SO₄(aq) → ZnSO₄(aq) + H₂(g)

(b) Dilute HCl

Zn(s) + 2HCl(aq) → ZnCl₂(aq) + H₂(g)

(c) Dilute HNO₃

Reaction with dilute HNO₃ is different as compared to other acids because nitric acid is an oxidising agent and it oxidises H₂ gas evolved to H₂O.

4Zn(s) + 10HNO₃(aq) → 4Zn(NO₃)₂(aq) + 5H₂O + N₂O(g)

(d) NaCl solution
Zn(s) + NaCl(aq) → Noreaction

(e) NaOH solution

Zn(s) + NaOH(aq) → NaZnO₂ (aq) + H₂(g)
Sodium Zincate

On adding a drop of barium chloride solution to an aqueous solution of sodium sulphite, white precipitate is obtained.

(a) Write a balanced chemical equation of the reaction involved.
Ans. Balanced chemical equation

NaSO₃(aq) + BaCl₂(aq) → BaSO₃(s) + 2NaCl(aq)

(b) What other name can be given to this precipitation reaction?
Ans. This reaction is also known as double displacement reaction.
(c) On adding dilute hydrochloric acid to the reaction mixture, white precipitate disappears. Why?
Ans. BaSO₃ is a salt of a weak acid (H₂SO₃) , therefore dilute acid such as HCl decomposes barium sulphite to produce sulphur dioxide gas which has the smell of burning sulphur
BaSO₃(s) + HCl → BaCl₂ + H₂O + SO₂(g)

You are provided with two containers made up of copper and aluminium. You are also provided with solutions of dilute HCl, dilute HNO₃ , ZnCl₂ and H₂O . In which of the above containers these solutions can be kept?

Copper is a nobel metal. It does not react with hydrochloric acid or with nitric acid. But aluminium is more reactive than copper. So, these acids should be kept in copper container.

Copper is less reactive than zinc and hence zinc chloride solution can be kept in copper container. But aluminium is more reactive than zinc and hence zinc chloride solution cannot be kept in aluminium container. For keeping water; both the containers can be used. However, copper is better.