pH of Solutions

Question

Calculate the pH of a 4.0 M HC2H3O2 solution. Ka= 1.8 x 10^10-5

Answer 1

Let HA represent the weak acid.

HA == H⁺ + A^-

Ka = [H+][A-]/[HA]

1.8x10^-5 = (x)(x)/4.0-x and assuming x is small relative to 4.0 M ..

x^{2 =} 7.2x10^-5

x = 8.5x10^-3 M = H⁺

pH = -log [H⁺] = 2.07 = 2.1