Question

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%

Answer 1

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.