Titration question

Question

A 20.0 mL sample of 0.150 M KOH is titrated with 0.125 M HClO4 solution. Calculate the pH after the following volumes of acid have been added: (a) 20.0 mL, (b) 23.0 mL, (c) 24.0 mL, (d) 25.0 mL, (e) 30.0 mL.

Answer 1

This answer uses the Henderson Hasselbach equation or HHeq for short. The equation is as follows pH = pKa + Log₁₀(cB/wa) where cB is the concentration of the base and wa is the concentration of the weak acid in mol/L. First you need to get the pH of the KOH which can be done by taking -Log₁₀(concentration of the base) to get the pOH and then taking 14 - pOH to get the initial pH plugging in we get .82 for pOH and 13.17 for pH. Using the found pH we can also get the pKa by solving for it in the HHeq pKa = pH - Log₁₀(cb/wa) with each concentration times .020 L we get the pKa = 13.09. Now we have pH = 13.09 + Log₁₀(.020L*.150/.020,.023,.024,.025,.030 L *.125 M) with the simple addition of adding the amount of acid added to the proportion. Plugging in the pKa we get a = 13.17, b = 13.10, c = 13.09, d = 13.07, e = 12.99. Note, I converted ml to l in the final two equations to make it compatible with mol/L. I hope this helps!