Finding pH of solution

Rron

A solution is prepared by mixing 200 mL of 0.2 M CH3COOH with 100 mL of 0.1 M of NaOH solution.Calculate the pH of the solution.(Ka=1.8x10^-5)

I really don't know how to start this, so please help me.Its gonna be a similar one on my exam tomorrow.

Thanks.

chemisttree

Assume the strong base completely converts the acetic acid to acetate. From there look at the expression which defines Ka for this acid. That's a start.

If you can't see it from that information, try looking over this information.

Borek

Hint: have you heard about buffers?

salger12

This is a buffer question. You will need to set up two ICE tables. The first one outlines the remaining concentration of weak acid and conjugate base after the reaction with OH-. The second should use those concentrations to determine the final pH. If you have a book, there should be an example.

Borek

Actually no need even for a single ICE table, this is almost a simple plug and chug application of the Henderson-Hasselbalch equation. You just need to start calculating concentrations of the reaction products, assuming reaction went to completion.

salger12

Correct, the Henderson-Hasselbalch equation is the preferred method. If this student does not know where to start, however, I figured writing out the concentration ratios would help in gaining some intuition.