Activity 2.9 NCERT Class 10 Science, Acids, Bases and Salts

Activity 2.9 NCERT Class 10 Science, Chapter 2 Acids, Bases, and Salts

Procedure:

Activity 2.9 asks us to react solid sodium chloride with concentrated sulphuric acid and check if the gas evolved turn the blue litmus paper into red or not.

Observation:

Gas fumes produce but do not turn the blue litmus paper into the red.

Explanation: 

Solid sodium chloride reacts with concentrated sulphuric acid and forms dry hydrochloric acid gas. Here HCl is produced in gaseous form as there is no water.

NaCl(S) + H₂SO₄(Conc.) ———> Na₂SO₄ (s)+ HCl(g)

A litmus paper works on H+  or OH- ion. Since there is no water in HCl gas, HCl does not dissociate into its ion and does not turn the blue litmus red.

HCl (aq) ——-> H⁺ + Cl^–

Inference/Conclusion:

Concentrated acids and bases need an aqueous medium to turn litmus paper.

Fact:

If we use moist blue litmus paper (as depicted in the diagram) then HCl gas will turn blue litmus paper into the red.

Next:  Activity 2.10: Dissolution of concentrated sulphuric acid in water produces heat,

See also: Activity 2.8: Acids, bases, and salt increase the electrical conductivity of the water.

Other activities from NCERT class 10 science Chapter 2.

 

Reference: NCERT textbook for class 10 Science.