Calculate the [H+] and pH of a 1.57 × 10-4 M acetic acid solution. The Ka of acetic acid is 1.76 × 10−5.

Answer 1

Let acetic acid be represented by HA.

HA ==> H⁺ + A^-

Ka = [H⁺][A^-] / [HA]

1.76x10^-5 = (x)(x) / 1.57x10^-4 - x

x² = 2.76x10^-9 - 1.76x10^-5x

x² + 1.76x10^-5x - 2.76x10^-9 = 0

Solve using the quadratic equation

x = [H⁺] = 4.45x10^-5 M

pH = -log [H⁺]

pH = -log 4.45x10^-5

pH = 4.35