Rebecca Tsarofski 2/21/19
Lab Partner: Olivia Mattos
Chem 201 Experiment 3
Measurement of Ka and Kb
Procedure: Please refer to page 4 of my laboratory manual for an outline of the general
procedure to be followed. There were no changes made to the experiment.
Experimental Data:
Solution
pH
0.10 M NH₄ᐩ
5.58
0.001 M NH₄ᐩ
6.56
0.10 M NH₃
11.20
0.001 M NH₃
10.09
Calculated Data:
Solution
[H₃Oᐩ]
[OH⁻]
[NH₄ᐩ]
[NH₃]
Ka or Kb
% Ionization
0.10 M NH₃
6.31 x 10⁻¹² M
1.59 x 10⁻³ M
1.59 x 10⁻³ M
0.1 M
2.56 x 10⁻⁵
1.6%
0.001 M NH₃
8.13 x 10⁻¹¹ M
1.24 x 10⁻⁴ M
1.24 x 10⁻⁴ M
0.001 M
1.54 x 10⁻⁵
12.4%
0.10 M NH₄Cl
2.63 x 10⁻⁶ M
4.00 x 10⁻⁹ M
0.1 M
2.63 x 10⁻⁶ M
6.92 x 10⁻¹¹
0.00263%
0.001 M
NH₄Cl
2.75 x 10⁻⁷ M
3.70 x 10⁻⁸ M
0.001 M
2.75 x 10⁻⁷ M
7.56 x 10⁻¹¹
0.0275%
Discussion:
In this experiment, my partner and I used a pH meter to measure the pH of certain
diluted solutions, as well as the two solutions of pH 4 and 7 provided for us. Then, we took 0.10
M Ammonium and Ammonia, a weak acid and a weak base, and diluted 1 mL with 99 mL of DI
water. We took samples of each, measured the pH, and then found the following data according
to those values.
According to the pH scale, my values do agree with the pH of weak acids and bases. For
the standard solution of 01. M NH3, my partner and I got a pH of 5.58, which seems good
because it is a weak acid. The more diluted sample had a pH of 6.56 because it was closer to
neutral when diluted with water. They were also similar to the values written on the board, so I
believe our values are pretty accurate. As solutions were diluted with water, the pH moved
closer towards 7.0, which is neutral. The standard value for Kb is 1.8 x 10⁻⁵ M, and both of my
Kb values were pretty close to that. For the standard solution of 0.1 M NH3, it had a Kb of 2.56 x