Ph of a solution?

Question

What is the pH of a solution prepared by mixing exactly 59.7 mL of 0.200 M HC2H3O2 with 21.1 mL of 0.400 M KOH? (Ka for acetic acid 1.8*10-5). Report your answer to 3 decimal places.

I got 8.959 for this question, but it was incorrect. Could anyone please tell me what they get and how they get it? Thanks.

Answer 1

1. work out 59.7 x 0.2/1000
2. work out 21.1 x 0.4/1000
3. subtract 2 from 1. This is the moles of acid left. Now divide by the total volume to get [acid].
4. the moles of salt is given by 2. Now divide by the total volume to get [salt].
5. you have a buffer solution. Apply the equation [H+] = Ka x [acid]/[salt]