Question

8) The Ka of hydrofluoric acid (HF) at 25.0 C is 6.8 x10-4. What is the pH of a 0.15 M aqueous 8) solution of HF? A) 4.60 B) 0.82 C)3.64 D) 1.17 E) 2.00

Answer 1

Kaof the acid is 6.8x104 Acid hydrolyis reaction is, Initial Change Equilbrium 0.15 0 0 0.15-х F-|H,O HF 6.8x 10.0 15 Assume x is much smaller than 0. 1 5 , so (0, 1 5-x) 0. 1 5 x -6.8x104 x 0.15 x=(1.02x10-4 ) x=1.01×10-2 M H,O-1.01x102 MM pH=-log [H30.] -log(1.01x10-2 2.00 Hence, the pH of HF is 2.00