Sorbic acid, HC6H702 (pKa=4.77), is widely used in the food industry as a preservative. For example, its potassium salt (potassium sorbate) is added to cheese to inhibit the formation of mold. What is the pH of 0.37M KC6H702(aq)?

Answer 1

Let's call sorbic acid HSorb.

HSorb ==> H^+ _ Sorb^-
Ka = (H^+)(Sorb^-)/(HSorb) = Ka.
So (H^+) = x
(Sorb^-) = x
(HSorb) = 0.37 - x
Substitute into the Ka expression and solve for x.
Note: It would be a good idea to convert pKa to Ka first.