Question

Identify the type of chemical reaction taking place in each of the following:

(a) Barium chloride solution is mixed with a copper sulphate solution and a white precipitate is observed. 

(b) On heating copper powder in the air in a china dish, the surface of copper powder turns black. 

(c) On heating, green coloured ferrous sulphate crystals, reddish brown solid is left and a smell of a gas having an odour of burning sulphate is experienced. 

(d) Iron nails when left dipped in blue copper sulphate solution become brownish in colour and the blue colour of copper sulphate fades away. 

(e) Quick lime reacts vigorously with water releasing a large amount of heat.

Answer 1

(a) Double displacement and precipitation reaction

When barium chloride solution is mixed with copper sulphate solution and a white precipitate is observed. 

In double displacement reaction, a precipitate is formed which settles down at the bottom. Any reaction that produces a precipitate is called a precipitation reaction. 

BaCl₂ + CuSO₄→ BaSO₄ (↓) + NaCl White ppt.

Note: A precipitate is a substance which is insoluble in water. 

(b) Oxidation reaction 

On heating copper powder in air in a china dish, the surface of copper powder turns black because copper undergoes oxidation in the presence of air. 

2Cu +O₂→ 2CuO Black

 (c) Thermal decomposition 

On heating green coloured ferrous sulphate crystals, reddish brown solid is left and smell of a gas having odour of burning sulphate is experienced. 

2FeSO₄(s) \(\overset{Heat}\longrightarrow\) Fe₂O₃(s) + SO₂(g) + SO₃(g)

In the above reaction, ferrous sulphate (FeSO₄) decomposes to ferric oxide (Fe₂O₃) 

(d) Displacement reaction 

Iron nails when left dipped in blue copper sulphate solution become brownish in colour and the blue colour of copper sulphate fades away.

Fe + CuSO₄→ FeSO₄ + Cu 

As we know that displacement reaction is a reaction in which one element displaces other element from its compound and takes its place there in. 

In the above reaction Fe replaces Cu and form a new compound. 

(e) Exothermic reaction 

Quick lime reacts vigorously with water releasing a large amount of heat: 

CaO + H₂O → Ca(OH)₂ + heat 

In the above reaction, the heat is released. Hence, it is an exothermic reaction. 

Exothermic reaction is a reaction in which heat is released when reactants changes into products.