Please find attached below the completed work. Kindly reply in case of any doubt.

Experiment No: 3

Determination of Ka, Kb, and % Ionization from pH

Name:
Date:

Experiment No: 3
Objective: The purpose of this experiment is to learn determination of acid dissociation
constant (K a ) and of base dissociation constant (K b ) . In addition, the purpose is to learn
percent dissociation that is a measurement of the extent of ionization (%) .
Results & Calculations:
pH of tap water =6.24
pH of de-ionized water =6.84
pH of outgassed water with bubbles=4.53

Solution

0

1

2

3

4

5

6

7

Molarity of

6.0M

1.2M

0.24M

0.048M

0.0096M

0.00192M

0.00038M

0.000768M

1.50

2.10

2.55

2.89

3.18

3.27

3.44

3.60

0.17

0.38

0.86

1.92

4.29

9.59

21.55

15.16

Ka of acetic acid

02.8  10 −5

5.26  10 −5

3.31  10 −5

3.46  10 −5

4.55  10 −5

1.50  10 −4

3.347  10 −4

8.22  10 −5

Calculated pH

1.98

2.34

2.69

3.04

3.39

3.74

4.09

3.93

HC 2 H 3O2
Experimental

pH

% Dissociation
=

x
 100
M

Taking

k a = 1.76  10 −5

Acetic acid is a weak acid which partially dissociates in water to produce H 3 O + ion and
the conjugate base CH 3 COO −
The initial concentration of acetic acid is M 0

CH 3COOH + H 2 O  CH 3COO − + H 3O +
M0 − x

x

x

Using the given value of K a and the equilibrium concentrations from the table, we have

Experiment No: 3

x2
= 1.76  10 −5
(M 0 − x )
x  M 0  1.76  10 −5 = 4.1952  10 −3 M 0

log (M 0 )
1
pH = − log H 3O + = 3 − log (4.1952) − log M 0  = 2.377 −
2
2





Discussion:
The system used for the measurement might have been inaccurate while carrying out
the lab. The equivalence point might also have been wrongly noted. If inaccurate
Molarity of samples were provided it may lead to wrong calculation. Moreover drops per
second might have been too slow or too fast, thus leading to faulty end point.

Experiment No: 3

Procedure Questions:
Question 1: What is the pH of the tap water? Was this value what you expected?
Why or why not? What ions contribute to the pH?
Answer 1: pH of the tap water is 6.24. However, the expected value of pH level of the
tap water is 6.5-9.5. Therefore, the pH of the tap water is below the expectation. The
number of hydrogen ions that the water will receive determines the pH.

Question 2: What is the pH of the deionized water? Was this value what you
expected why or why not?
Answer 2: pH of the de-ionized water is 6.85. The pH of the de-ionized water is below
the expectation as pH of the de-ionized water is 7.
Question 3: What is the pH of the out gassed water? Why did the pH change?
Answer 3: pH of the out gassed water is 4.43. Out gassing p...