Question

A) Determine the [H3O+] of a 0.240 M solution of formic acid.

B) Determine pH of this solution of formic acid.

Answer 1

Ka of formic acid = 1.8 x 10^-4

HCOOH + H2O -----------------> HCOO - +   H3O+

0.240                                                 0                 0

0.240 - x                                           x                   x

Ka   = [HCOO-][H3O+]/ [HCOOH]

1.8 x 10^-4 = x^2 / 0.240 - x

x = 0.0065

[H3O+] = 0.0065 M

pH = - log [H3O+] = -log (0.0065)

pH = 2.19