Question

In: Chemistry

Calculate the pH of a 25 mg/L solution of hydrofluroic acid. HF = H+ + F-...

Calculate the pH of a 25 mg/L solution of hydrofluroic acid.

HF = H+ + F- Ka=10^-3.2

Expert Solution

25 mg / L = 25 x 10^-3 g / L

molarity = 25 x 10^-3 / 20 mol / L

= 0.00125 M

HF <------------------> H+ + F-

0.00125 0 0 -------------> initial

-x +x +x ------------> change

0.00125-x x x -------------> equilibrium

Ka = [H+][F-]/[HF]

10^-32 = x^2 / 0.00125 - x

x^2 + 6.31 x 10^-4 x - 7.89 x 10^-7 = 0

x = 6.27 x 10^-4

x = [H+] = 6.27 x 10^-4 M

pH = -log [H+

pH = -log (6.27 x 10^-4 )

pH = 3.20

queen_honey_blossom answered 2 years ago

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