CBSE Class 10 Answered

Dear Student,

(a)     

A = NaCl, B = NaHCO₃, C = NaHSO₄

Aqueous solution of salt NaHSO₄ is acidic since the salt is a result of strong acid and weak base. Hence, the salt solution of C is acidic.

(b)      

(i)                  The pH of the salt solution of A must be 7 (Neutral). When NaOH is added to the salt solution of A which has pH 7, the pH shifts to the alkaline side due to the addition of alkali. Phenolphthalein changes its colour from colourless to pink in an alkaline medium.

(ii)                Aqueous solution of salt NaHSO₄ is acidic since the salt is a result of strong acid and weak base. In an acidic medium, the blue litmus solution changes to red while the colour of the red litmus solution remains the same.

OR

(b)    Aqueous solution of A i.e. sodium chloride is termed as Brine. When electricity is passed through the brine, the following reaction takes place.

2NaCl(aq) + H₂O(l) ⟶ 2NaOH(aq) + Cl₂(g) + H₂(g)

At the anode (positive electrode), chlorine gas is evolved and at the cathode (negative electrode), hydrogen gas is evolved. Sodium hydroxide is formed near the cathode.

Use of Sodium chloride: It is used in cooking and is known as common salt.