Exercise 8 | Buffers and Titration of Acids and Bases

Consider a solution initially containing 0.40 mol fluoride anion and 0.30 mol of hydrogen fluoride.

What is the pH after addition of 0.20 mol of HCl to this solution?


Data: pKa (HF/F-) = 3.14

The titration equation is:

Reaction: F- + H3O+ HF + H2O

 

After adding 0.20 mol of HCl:

nF-,0 = 0.40 mol

nH+,0 = 0.20 mol

H3O+ is the limiting reagent.

nF- = nF-,0 - nH+,0 = 0.20 mol

nHF = nHF,0 + nH+,0 = 0.50 mol

 

Henderson-Hasselbalch equation can be used:

pH = pKa + log base0acid0

pH = 3.14 + log 

pH = 2.74