Determination of k a values 5 pt s k graphical

Table 3. Determination of K
a
Values
5
pt
s
K
Graphical Analysis Literature Values
V
1/2
(mL) p K
a
K
a
p K
a
K
a
K
a1
5.25 3.07
8.51E-
4 2.12 7.50E-3
K
a2
18.00 5.97 1.07E-6 7.21 6.20E-8
p K
a1
calculated from initial pH 2.48

IV. Discussion
a. Discussion of standardization
i. The objectives of part A of the experiment was to use the standardization
reaction to determine the exact concentration of NaOH. In order to do this,
the indicator phenolphthalein was used to determine the endpoint of the
titration or when the equivalence point had been reached and the
neutralization was complete. This concentration of NaOH was used in the
calculations of part B of the experiment.
ii. The mean concentration of NaOH is 0.008405 and the standard deviation
is
1.001*10 -4 .
iii. Sample Calculation: Concentration of sodium hydroxide
M NaOH =
0.069 gKHP
39.5 = 70 mL NaOH
∗ 1 mol KHP
204.23 g KHP
∗ 1 mol NaOH
1 mol KHP
∗ 1000 mL
1 L
M NaOH = 0.008510 M
iv. For the two trials of standardizing NaOH, the concentration differed by
only 0.0002. This difference is extremely is extremely small and
negligible which explains why the titrations are fairly accurate. However,
there is still a variance and this is due to the subjective nature of the color
change of the indicator. Often times, it is extremely difficult to determine
the exact moment when the indicator changes color so it is easy to
accidently add a few extra mL’s of water.
b. Discussion of Titration of Cola