Problem:

A 25.00 mL sample of an unknown monoprotic acid (HA) was titrated with 0.5 mol/L NaOH. The pH of the resulting solution was measured after the addition of NaOH to the acid. Determine the Ka of the unknown acid and its identity.

Procedure:

1. Graph the data from the table below.

Volume of NaOH added (mL)	pH	Volume of NaOH added (mL)	pH
0	2.79	6.4	5.58
2	4.33	6.6	5.69
3	4.59	6.8	5.84
4	4.83	7.0	6.05
5	5.08	7.2	6.42
5.2	5.14	7.4	10.79
5.4	5.19	7.9	11.89
5.6	5.26	8.4	12.16
5.8	5.32	8.9	12.37
6.0	5.40	9.4	12.44
6.2	5.48	9.9	12.53

2. From the graph, determine the equivalence point.

3. Calculate the molar concentration of the acid.

4. Write the Ka expression for the ionization of HA in water.

5. Determine the initial [H3O+] (before the addition of NaOH).

6. What is the initial concentration of A-?

7. Determine the Ka value for the unknown acid.

8. What is the identity of the acid?