CHEM 212 Laboratory
Dissociation constant of acids and bases
Data Analysis Supplement
Reference: General Chemistry Laboratory Experiments, Suzanne W Slayden, 1999, 3rd edition, Pages
155-164
Data: After you have noted down all the molarities, volumes and pH’s, enter your own data into the
appropriate Web-based data entry form, using a computer in the lab. In your measurements and
calculations, remember to pay attention to uncertainties and significant figures.
Results: Outside of class, retrieve your data in spreadsheet form (along with that of the entire class) from:
http://chem.gmu.edu/results/. Then use Excel to calculate the [H+]A1, [HA]A1,
[H+]A2, [A-]A2, [HA]A2, Ka _A1, Ka _A2, and Ka _ave.
Your lab report should include the following in addition to the pages from your lab notebook:
 An Excel sheet “Raw Data” showing the raw data for the entire class (as downloaded). A typical
example of the raw data sheet is shown below:
Raw Data
A
B
C
D
E
F
G
1
ID M_HAc pH_HAc M_NaOH V_NaOH V_HAc pH_buffer
M
ml
ml
2
1
0.096
2.86
0.101
8.11
19.96
4.35
3
2
0.096
2.83
0.101
8.05
20.01
4.44
M
Explanation:
o M_Hac: molarity of acetic acid solution
o pH_Hac: pH of acetic acid solution
o M_NaOH: molarity of sodium hydroxide solution
o V_NaOH: volume of sodium hydroxide solution
o V_Hac: volume of acetic acid solution
o pH_buffer: pH of the buffer solution. A buffer was produced when NaOH was added to
the acetic acid solution.

A 2nd Excel sheet “Results” showing the calculated results for each student in the class –
each in a separate row. Make sure to show an example calculation for each column. This
can be done by copying the equation from the formula bar to a blank cell below the
elements in the table An apostrophe in front of it makes it text instead of an equation.
Each table should be formatted as in previous classes with lines separating the table
headings from the contents. A line below the contents should also be drawn. A typical
example of the results sheet is shown below:
1
Results
A
B
C
E
F
G
H
Ka_A2
Ka_ave
2
0.0014 0.0941 4.47E-05 0.0292 0.0387 2.02E-05 3.37E-05 2.70E-05
3
0.0015 0.0940 3.63E-05 0.0290 0.0391 2.33E-05 2.69E-05 2.51E-05
M
M
[A-]A2 [HA]A2
Ka_A1
[H+]A1 [HA]A1
M
[H+]A2
D
1
M
M
Explanation:
o [H+]A1: [H+] of acetic acid
o [HA]A1: [HA] of acetic acid
o [H+]A2: [H+] after addition of NaOH.
o [A]A2: [A] after addition of NaOH.
o [HA]A2: [HA] after addition of NaOH.
o Ka_A1: Ka of acetic acid. This was calculated using the pH and initial concentration of
the acetic acid.
o Ka_A2: Ka of acetic acid. This value is calculated after addition of NaOH. Remember
that for every mole of NaOH added you form one mole of acetate anion (A).
o Ka_ave: average Ka of acetic acid and the mixture

A 3rd Excel sheet “Histogram-1” showing a histogram of the distribution of the Ka results for
acetic acid. Use equally spaced “bins” chosen to display the “spread” in the class results.

A 4th Excel sheet “Histogram-2” showing a histogram of the distribution of the Ka results for the
mixture of acetic acid and sodium hydroxide. Use equally spaced “bins” chosen to display the
“spread” in the class results.
Printing Tables:
 Large tables should be printed in the landscape mode and sometimes it might be necessary to go
to “page setup” and select “Fit to 1 page” to make the page fit on one page.
 Include column and row headings on the printout so that the instructor can more easily
understand equations used. This can be done by going to File → Page Setup → Sheet tab →
Select “Row and Column Headings”.
Discussion: In your discussion section address the following questions:
 How does the degree of disassociation affect Ka or Kb?
 What precautions do you need to take while standardizing the pH meter?
 What are the possible sources of error in this experiment? Refer in your answer to the class
histogram as well as to your own results.
 How well do your results (and the class’s) agree with the literature value? Compare each result
and the average with the literature value.
 Are the deviations systematic or random?
 What are the possible sources of error in this experiment? Refer in your answer to the class
histogram as well as to your own results.
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