# Problem: A buffer contains 0.16 mol of propionic acid (C2H5COOH) and 0.22 mol of sodium propionate (C2H5COONa) in 1.20 L.What is the pH of the buffer after the addition of 0.02 mol of NaOH?

###### FREE Expert Solution

Henderson-Hasselbalch equation.

C2H5COONa will break up in the solution

▪ C2H5COO-  weak base (conjugate base)
[C2H5COO-] = [C2H5COONa

▪ Na+ → neutral ion  will not contribute to pH

C2H5COOH → weak acid

• The solution is composed of a weak acid and its conjugate base, therefore we have a buffer.

Step 1: Calculate the pKa of the weak acid.

Calculate pKa:

Ka C2H5COOH = 1.34x10-5

pKa = 4.87

Step 2: Create an ICF chart and determine the final amounts of species present after the reaction.

▪ weak acid + conjugate base = buffer

Step 3: Calculate the pH of the solution.

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###### Problem Details

A buffer contains 0.16 mol of propionic acid (C2H5COOH) and 0.22 mol of sodium propionate (C2H5COONa) in 1.20 L.

What is the pH of the buffer after the addition of 0.02 mol of NaOH?