Answer to Question #140507 in General Chemistry for Ashley

Question

A solution contains 0.428 M sodium fluoride and 0.284 M hydrofluoric acid.

Calculate the pH of this solution. The Ka of HF is 7.20×10-4.

pH =

Answer 1

HF - weak acid ;

NaF - its conjugate base;

The Henderson–Hasselbalch equation:

pH = pKa + lg([F-]/[HF]);

pK_a=-lg(K_a);

pH=-lg(7.2*10^-4) + lg(0.428/0.284) =3.3

Answer: pH=3.3