Hydrolysis Of Salts

Question

Which of the following aqueous salt solutions will be basic (pH > 7) at 25°C due to hydrolysis of its ions?

RankGuru · Accepted Answer

Salt hydrolysis depends on the nature of the acid and base from which the salt is derived. Na_2CO_3 is a salt of strong base NaOH and weak acid H_2CO_3; in water, the carbonate ion undergoes anionic hydrolysis: CO_3^{2-} + H_2O \rightleftharpoons HCO_3^- + OH^-, producing OH^- ions that make the solution basic (pH > 7). NH_4Cl is wrong because it is a salt of strong acid HCl and weak base NH_3; the ammonium ion undergoes cationic hydrolysis producing H^+ ions, giving an acidic solution (pH < 7). NaCl is wrong because it is a salt of strong acid HCl and strong base NaOH; neither Na^+ nor Cl^- hydrolyse appreciably, so the solution is neutral (pH = 7). FeCl_3 is wrong because it is a salt of strong acid HCl and weak base Fe(OH)_3; Fe^{3+} undergoes extensive hydrolysis producing H^+ and a highly acidic solution. The NCERT Equilibrium chapter classifies salt hydrolysis systematically based on the strength of the parent acid and base. Plausibility check: Na_2CO_3 solution is used as a cleaning agent (washing soda) precisely because of its basicity, confirming our answer.

Hydrolysis Of Salts

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