Titration question

Question

When a 21.1 mL sample of a 0.403 M aqueous hydrocyanic acid solution is titrated with a 0.420 M aqueous sodium hydroxide solution, what is the pH at the midpoint in the titration

Answer 1

Hi Chastity,

 

It's not totally clear what is meant by "midpoint in the titration," but a reasonable guess is that it is the half-equivalence point.

 

Working form there, and applying the Henderson-Hasselbalch equation, it becomes apparent that, at this point in the titration, the pH is equal to the pKa of the weak acid. Find the Ka of hydrocyanic acid, calculate the Pka from that number, and there is the answer.

 

Jim Scripko