A solution of hydrofluoric acid (0.27 M, 10.00 mL) was titrated with 15.0 mL of 0.13 M sodium hydroxide (K_a of hydrofluoric acid = 7.20 $\times$ 10^-4). What is the final pH of this solution?

Question

Quizplus · Accepted Answer

The reaction between HF and NaOH forms water and the salt NaF. After the reaction, the solution contains NaF, which is a weak base. The pH is determined by the hydrolysis of F⁻ ions. Using the Kb of F⁻ (calculated from Kw/Ka), the concentration of OH⁻ can be found, and thus the pH is approximately 3.56.

A Solution of Hydrofluoric Acid (0 ×\times× 10-4)

A Solution of Hydrofluoric Acid (0 $\times$ 10^-4)