Problem: A 1.50 L buffer solution is 0.250 M HF and 0.250 M NaF. What is the pH of the solution after the addition of 0.0500 moles of solid NaOH? Assume no volume change. Ka for HF is 3.5 x 10-4.

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FREE Expert Solution

The buffer solution is composed of HF and NaF. These two components will break up in the solution:

HF(aq) H+(aq) + F-(aq)

NaF(aq) Na+(aq) + F-(aq)


HF is a weak acid and based on the Bronsted-Lowry definition, an acid is a proton (H+). Once HF loses its proton, its conjugate base is formed:

HF(aq)  +   H­2O(l)  →   F(aq)   +   H3O+(aq)
(weak acid)    (base)     (conjugate base)    (conjugate acid)

Whenever we have a conjugate base and a weak acid, we have a buffer.

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Problem Details

A 1.50 L buffer solution is 0.250 M HF and 0.250 M NaF. What is the pH of the solution after the addition of 0.0500 moles of solid NaOH? Assume no volume change. Ka for HF is 3.5 x 10-4.