Question

the pH value of an aqueous solution of hydrochloric acid is 2. what is the pH value of the solution after the addition of 10 g of sodium chloride?

Answer 1

Hydrochloric acid is a strong acid, it ionizes completely in aqueous solution. It is not a weak acid, therefore, no equilibrium is set up between unionized solute and the solution. NaCl is a neutral salt and it's addition to a solution of HCl has no effect on the pH of the solution, a phenomenon called "Common ion effect." This does not occur because HCl is a strong acid and ionizes completely in aqueous solution. Had it been a weak acid, the common ion Cl- will lower the ionization of the acid, causing the pH to reduce.

Therefore, the pH after the addition of 10g of NaCl to the solution still remains 2.(fairly constant)