What is the pH of the solution which results from mixing 25ml of 0.30M HF(aq)and 25ml of 0.30M NaOH(aq)

Question

at 25 degree celcius?

(ka of HF=7.2x10-4)

Answer 1

0.025 litres @ 0.30 mol/litre - 0.0075 moles HF

0.025 litres @ 0.30 mol/litre - 0.0075 moles NaOH

they produce 0.0075 moles of NaF which in 0.050 litres  = 0.15 molar F-

that hydrolyses:

F- in water => HF & OH-

Kh = Kwater/ Ka = 1e-14 / 7.2e-4 = 1.39e-11

1.39e-11 = [HF] [OH-] / [HF]

1.39e-11 = [x] [x] / [0.15]

x = [OH-] = 1.44e-6

pOH = 5.84

14 - pOH = pH

your answer: pH = 8.16