Calculate the percent ionization of 0.120 m lactic acid in a solution containing 8.5×10−3 m sodium lactate.
express the percent ionization to two significant digits.

1.62 %

Explanation:

Percent ionization can be expressed as:

[H⁺]/[HA] * 100%

We're already given [HA], the molar concentration of lactic acid (0.120 M), so now we need to calculate [H⁺].

To do that we can use the Henderson-Hasselbach equation:

pH = pKa + log [A⁻]/[HA]

The pKa of lactic acid is 3.86, and we're given the concentrations of lactic acid and its salt (sodium lactate):

pH = 3.86 + log [8.5x10⁻³]/[0.120]

pH = 2.71 = -log [H⁺]

= [H⁺]

[H⁺] = 1.95x10⁻³M

Finally we calculate the percent ionization:

1.95x10⁻³ / 0.120 = 1.62 %

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