How are percent ionization values similar to equilibrium constant values? Explain your reasoning and identify which weak acid would have the smallest equilibrium constant.

Weak Acid

Percent Ionization

HNO2

6.2%

HClO2

28.2%

HCN

0.007%

The greater the percent ionization the larger will be the equilibrium constant.

Consider the HCN which is 0.007% ionization. For a 0.10 M solution, 0.00007 (.10) will give the [H+] = 7 x 10^-6

K = [H+][CN-]/[HCN]

K = 7 x 10^-6 * (7 x 10^-6) / 0.1

K = 4.9 x 10^-10

Consider the HClO2 which is 28.2%. [H+] = 0.28 (0.10) = 0.028. Substituting in the K expression

0.028 (0.028) / 0.10 - 0.028 which will give a larger equilibrium constant.