Question

Calculate the pH at the equivalence point for the following titration: 0.100 M NaOH versus 1.60 g formic acid (HCO2H Ka = 1.8 x 10-4)

Answer 1

At the equivalence point we have a solution of sodium formate. As both concentrations of titrated acid and titrant are identical, and monoprotic formic acid reacts 1:1 with sodium hydroxide, we have to add identical volume of base to the given volume of acid. That in turn means that final volume is twice that of initial volume of acid sample, so after dilution concentration of formate must be half that of acid - that is 0.05 M.

We have titrated weak acid, so to calculate pH we have to calculate concentration of OH- from formate hydrolysis first. Formate is a weak base with