exp 05 complete

3.5 Kinetics of the Alkaline Hydrolysis of Crystal Violet in aqueous solution in the presence of a Cationic and an Anionic Surfactant.
3.5.1 THEORY
The alkaline hydrolysis of crystal violet, a carbocationicdye(CV+) takes place according to CV+ + OH- ↔ CVOH
Where CVOH is the colorless carbinol form of the dye.

The kinetics of the reaction can be monitored due to the carbocation form of the dye by measuring the decrease in absorbance at the wavelength corresponding to the absorption maximum(λmax). The hydrolysis is carried out by using a large excess of NaOH (more than 10-fold) with respect to the substratecrystal violet such that the reaction (CV+ +
OH-↔ CVOH) obey the pseudo-first order reaction rate equation
-d[CV+]/dt = kw[CV+][OH-]=k[CV+]
Where k=kw[OH-] is the pseudo-first order rate constant and kw is the second order rate constant. Assuming the absorbance at the λmax of the reaction mixture to be due to the
CV+ only, we obtain ln(A0/A)=kt Where A0 is the initial absorbance and A is the absorbance at time t.

33

3.5.2 Experimental data with graphs & calculations

Figure: Verification of Beer- Lambert's Law

1.6
1.4

Absorbance

1.2
1.0
0.8
0.6
0.4
0.2
0.0
0

5

10

15

Concentration (M) X 10

20

25

6

Table-01: Determination of molar extinction co-efficient
Concentration x 106
M

Absorbance

5
10
15
20
25

0.2430
0.4930
1.0140
1.1920
1.5110

Molar extinction co-efficient (ξ ) mol-1Lcm-1

0.06470

34

Table- 02: Determination of maximum absorbance of crystal violet during alkaline hydrolysis at different time
Time (min)
1.0000
3.0000
5.0000
7.0000
10.0000
13.0000
17.0000

Maximum absorbance
0.2840
0.2450
0.2110
0.1880
0.1440
0.1220
0.1010

Figure: A plot of Maximum Absorbance vs. Time for CV
0.30

Absorbance

0.25

0.20

0.15

0.10

0.05
0

5

10

15

20

25

Time( min)

35

Figure: Absorbance vs. Time plot for kinetics of Hydrolysis of CV
0.7
0.01M NaOH
0.02 M NaOH
0.04 M NaOH
0.06 M NaOH

0.6

Absorbance

0.5

0.4

0.3

0.2

0.1

0.0
0

200

400

600