Question

Write the chemical equation of the reaction with an example each in which the following change has taken place:

(i) Change in colour

(ii) Change in temperature 

(iii) Formation of precipitate.

Answer 1

(i) Change in colour:

The reaction between lead nitrate solution and potassium iodide solution.

Pb(NO₃​)₂​(aq) + 2KI → PbI₂​(s) + 2KNO₃​(aq)

In this reaction colour changes from colourless to yellow.

(ii) Change in temperature:

The action of dilute sulphuric acid on zinc.

Zn(s) + H_2​SO₄​(aq) → ZnSO₄​(s) + H_2​(g)

In this reaction, heat is evolved.

(iii) Formation of precipitate:

The action of barium chloride on sodium sulphate.

BaCl₂​(aq) + Na₂​SO_4​(aq) → BaSO₄​(s) + 2NaCl(aq)

Answer 2

(i) Change in colour: Reaction between lead nitrate solution and potassium iodide solution.

Pb(NO₃)₂(aq)+2KI → PbI₂(s)+2KNO₃(aq)

In this reaction, colour changes from colourless to yellow.

(ii)Change in temperature: Action of dilute sulphuric acid on zinc.

Zn(s) + H₂SO₄(aq) → ZnSO₄(aq) + H₂

In this reaction, heat is evolved

(iii) Formation of precipitate: Action of barium chloride on sodium sulphate.

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

BaSO₄(s) - ppt