lab 3

Determination of Ka for a Weak Acid

Peter Jeschofnig, Ph.D.

Version 42-0151-00-01

Lab Report Assistant This document is not meant to be a substitute for a formal laboratory report. The Lab Report Assistant is simply a summary of the experiment’s questions, diagrams if needed, and data tables that should be addressed in a formal lab report. The intent is to facilitate students’ writing of lab reports by providing this information in an editable file which can be sent to an instructor.

Data Table 1: Determine the Volume of a Drop
	Number of Drops
1 mL	18
2 mL	20
3 mL	19
Average Drops \ mL	19
Average mL \ Drop	0.053

Observations Part 2

Data Table 2: Trials and Average
	Trial 1	Trial 2	Trial 3	Average
Volume – acid (ml)	2.0 mL	2.0 mL	2.0 mL	2.0 mL
Color of acid	3.5ph	3.5ph	3.5ph	3.5
Volume – NaOH (drops)	42	42	41	42
Color – final solution	Light Pink	Light Pink	Light Pink	Light Pink

Experiment

Determination of Ka for a Weak Acid

105

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Data Table 3: Volume of NaoH
NaOH added - drops	NaOH added - ml	pH
0	0.000	3.500
2	0.053	3.714
4	0.106	3.928
6	0.159	4.142
8	0.212	4.356
10	0.265	4.570
12	0.318	4.784
14	0.371	4.998
16	0.424	5.212
18	0.477	5.426
20	0.530	5.640
22	0.583	5.854
24	0.636	6.068
26	0.689	6.282
28	0.742	6.496
30	0.795	6.710
32	0.848	6.924
34	0.901	7.138
36	0.954	7.352
38	1.007	7.566
40	1.060	7.780
42	1.113	8.00
44
46
48
50
52
54

Questions

A. What is the relationship between Ka and pKa?

B. What are the potential sources for errors in this experiment?

C. If your experimental Ka is 5.3 and the actual Ka of your unknown acid is 4.7, what is your %

error?