Which statement correctly describes the pH behavior of a salt formed from a weak base and a strong acid?

Which statement correctly describes the pH behavior of a salt formed from a weak base and a strong acid?

• A. It yields an acidic solution due to hydrolysis of the conjugate acid.
• B. It yields basic solution due to conjugate base hydrolysis.
• C. It yields neutral solution regardless of identity.
• D. It yields a highly unstable pH that cannot be predicted.

Answer: (A)

When a salt forms from a weak base and a strong acid, the pH is governed mainly by the hydrolysis of the cation, which is the conjugate acid of the weak base. This conjugate acid donates a proton to water: BH+ + H2O ⇌ B + H3O+. That production of hydronium ions makes the solution acidic. The anion, coming from a strong acid, is the conjugate base of a strong acid and is a very weak base, so it doesn’t significantly hydrolyze to generate OH-. Therefore it doesn’t counteract the acidity. Net result: the solution is acidic. For example, ammonium chloride from ammonia (a weak base) and HCl (a strong acid) yields an acidic solution because NH4+ hydrolyzes to release H3O+.

When a salt forms from a weak base and a strong acid, the pH is governed mainly by the hydrolysis of the cation, which is the conjugate acid of the weak base. This conjugate acid donates a proton to water: BH+ + H2O ⇌ B + H3O+. That production of hydronium ions makes the solution acidic. The anion, coming from a strong acid, is the conjugate base of a strong acid and is a very weak base, so it doesn’t significantly hydrolyze to generate OH-. Therefore it doesn’t counteract the acidity. Net result: the solution is acidic. For example, ammonium chloride from ammonia (a weak base) and HCl (a strong acid) yields an acidic solution because NH4+ hydrolyzes to release H3O+.