A sample of 0.314g of unknown monoprotic weak acid, HA was dissolved in 25.00 mL of water and titrated with 0.1M KOH. The acid required 27.20 mL of the base to reach equilibrium point.

Question

Find the pH of the solution if 40 mL KOH is added to the acid solution.

My question is how I determine the acid dissociation constant with these information in order to find pH of solution.

Answer 1

HA + KOH ==> KA + H2O

If the acid requires 27.20 mL of 0.1M KOH to reach the equivalence, then 40 mL of the 0.1M KOH will neitralize all of the acid and have excess KOH reamaining. Therefore, the excess KOH will determine the pH of the solution and the Ka for the HA is not needed.

Answer 2

Thank you very much.