CHM-202 General Chemistry and Laboratory II
Laboratory 7
Acids and Bases: pH Determination and Buffer Capacity
Name
Group
Results
Dilution of Acids and Bases
pH of distilled water is
Solution
A.
HCl
Conc.
pH
Color
B.
HOAc
pH
Color
C.
NaOH
pH
Color
D.
NH3
pH
Color
pH of tap water is
1
10-2 M
2
10-3 M
3
10-4 M
4
10-5 M
5
10-6 M
6
10-7 M
Buffer dilution
Solution
1
10-2 M
2
10-3 M
3
10-4 M
4
10-5 M
5
10-6 M
6
10-7 M
5x10-2 M
5x10-3 M
5x10-4 M
5x10-5 M
5x10-6 M
5x10-7 M
Undiluted
1:10
1:100
1:1,000
1:10,000
1:100,000
Conc.
A.
Buffer
pH
Color
Conc.
B.
HOAc/NaOAc
pH
Color
Conc.
C.
Lemonade
pH
Color
Buffer
Capacity
10-2 M Buffer
Distilled H2O
HOAc/NaOAc
Lemonade
Initial pH
Volume added
(Buffer Solution)
Final pH
Volume of
NaOH Added
Questions
1.
Calculate the number of grams of NaOH per 100 mL to give a pH 8.0 solution if pure water at pH 7.0 is
used in the experiment. Repeat this calculation for a pH 6.0 solution using HCl. Comment on how this
would or would not explain the fact that distilled and tap water are not exactly at a pH value of 7.000.
2.
Compare the pH values in the dilution experiment for each of the acids and bases used to the pH
determined for distilled water. Do the pH values for the more dilute solutions approach the pH of the
distilled water? What would you predict the pH to be if you diluted the 10-7 M HCl solution by a factor of
10?
3.
Compare the pH values in the dilution experiment for the strong acid (HCl) and the weak acid (acetic
acid). Do they both have the same pH values at the same concentrations? Do the pH values increase at the
same rate across the wells?
4.
What is the effect of dilution on the buffer solution? What is the effect of dilution on the acetic
acid/sodium acetate solution? On the pH of the lemonade solution?
5.
Compare the volumes of base used to change the pH by 1 unit for water, buffer, acetic acid/sodium
acetate solution and lemonade (note that you used less lemonade than the other solutions). Do the latter
two solutions behave more like the buffer or water?