Exercise 1: Determination of K a Data Table 1. Determination of Equivalence Poin
ID: 992512 • Letter: E
Question
Exercise 1: Determination of Ka
Data Table 1. Determination of Equivalence Point.
Trial 1
Trial 2
Volume of Unknown Weak Acid
4 mL
4 mL
Total Number of Drops Required to Reach Equivalence Point
5
5
Average Number of Drops
5
Data Table 2. Titration Curve Values.
Drops NaOH Added
pH Value
Trial 1
pH Value
Trial 2
pH Value
(Average)
Half-Equivalent Point = ( Drops)
2.5
2.5
2.5
Equivalent Point = ( Drops)
5
5
5
0
3.5
3.5
3.5
10
4.5
4.5
4.5
20
5.5
5.5
5.5
30
7.0
7.0
7.0
40
8.0
8.0
8.0
50
10.0
10.0
10.0
60
10.0
10.0
10.0
70
10.0
10.0
10.0
80
10.0
10.0
10.0
90
10.0
10.0
10.0
100
10.0
10.0
10.0
110
10.0
10.0
10.0
120
10.0
10.0
10.0
Data Table 3. Determination of Unknown.
pKa of Unknown Weak Acid:
Ka of Unknown Weak Acid:
Unknown Weak Acid Identity:
% Error pKa:
% Error Ka:
Please fill in the values in the chart?
Trial 1
Trial 2
Volume of Unknown Weak Acid
4 mL
4 mL
Total Number of Drops Required to Reach Equivalence Point
5
5
Average Number of Drops
5
Explanation / Answer
Chart for titration of weak acid with strong base
pKa of unknown acid = pH at half equivalence point = 2.5
pKa = -log[Ka]
Ka of unknown acid = 3.16 x 10^-3
Unknown weak acid Identity = Citric acid
% error pKa = [(2.79 - 2.5)/2.79] x 100 = 10.39%
% error in Ka = [(3.16 x 10^-3 - 1.62 x 10^-3)/3.16 x 10^-3] x 100 = 4.9%
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