Question

1st table: Standardization Data Table

2nd table: Equivalent Mass Data Table

3rd table: pKa data table

	Trail 1
mass KHP, g	.44
final volume, mL	36.10
initial volume, mL	11.2
volume of NaOH added, mL	24.9

	Trail 1
mass acid, g	.36
final volume, mL	59.60
initial volume, mL	4.30
volume of NaOH	55.30

buret reading (mL	pH
1.7	2.53
2.80	2.59
3.75	2.65
4.80	2.75
5.85	2.85
6.95	2.93
7.85	3.01
8.80	3.09
10.3	3.21
11.4	3.31
12.9	3.42
13.8	3.51
14.9	3.61
16.1	3.72
16.9	3.81
18.2	3.92
19.05	4.01
20.2	4.23
21.20	4.41
22.6	4.53
23.6	4.73
24.75	5.12
26.19	5.20
26.4	5.29
26.65	5.4
27.0	5.56
27.30	5.84
28.39	9.47
29.55	10.85
30.85	11.28
31.99	11.49
32.80	11.59
38.4	12.01

Using the data above answer the following questions:

1. From the standardization data, calculate the molarity of the sodium hydroxide for each trial. Average the values and enter the average in the Standardization Data Table.

2. From the equivalent mass data, calculate the equivalent mass of the unknown acid for each trail. Average the values and enter the average in the Equivalent Mass Data Table.

3. Why is equivalent mass determined and not molar mass?

4. Why must the KHP and the acid samples be dried? If they are not dried, how would the results change (high or low)?

5. Why must NaOH be standardized? Why can't an exact solution of NaOH be prepared?

6. From the graph of pH versus volume of NaOH, determine the pKa of the unknown acid. Convert this value to Ka.

7. Why is the equivalence point in the titration of the unknown acid with sodium hydroxide not at pH 7?