Kinetics of the
Decomposition of Crystal
Violet Indicator
Purpose

To conduct an experiment that
will collect data and determine
the order of a chemical
reaction.
Concept

Kinetics is the branch of
chemistry that describes the
rates of reactions and their
mechanisms.
 Application is left to the student
Safety



H
Crystal Violet 1
0.10M NaOH 2
F
0
0
R
1
2
Special
Stains
Caustic
Setup Procedure.1

Set up the CBL-2 with a graphing
calculator and a colorimeter in
channel 1.
Setup Procedure.2





Calibrate the
colorimeter
Set the dial to 0%T;
Calibrate point 1 at 0.
Place a cuvette
with dH2O in
the colorimeter.
Setup Procedure.3


Set the dial to 656nm (Green);
Calibrate point 2 at 100.
Return to the main screen.
Setup Procedure.4


Set the mode to time graph
Use these values to run the
experiment.
Setup Procedure.5

Return to the main screen
Reaction Procedure.1

Begin the reaction.
• Add 10 ml of NaOH
and the 80 ml of
distilled water to a
clean beaker and
stir.
10 ml of CV
80 ml of dH2O
10 ml of NaOH
Reaction Procedure.2
• Add 10 ml of Crystal Violet
solution to the beaker and stir.
Reaction Procedure.3
• Obtain an aliquot of
the reaction and place
it in a cuvette.
• Insert the cuvette into
the colorimeter and
start recording the
data with the CBL-2.
Start
Reaction Procedure.4

The calculator will display the
data as it is collected and
graphically track the progress
of the reaction.
Reaction Procedure.5

Once the CBL-2 has finished
collecting data it will display a
graph of the collected data.
Reaction Procedure.6

Clean up all the glassware and
the cuvette then return the
equipment as directed. Rinse
all glass ware with dH2O and
dry before storing. Do not wipe
the cuvette dry with any thing
other than the optical wipes.
Data

In this experiment the data was
automatically collected by the
CBL-2 and stored in the
graphing calculator. Nearly 200
data points were collected. For
convenience they are not listed
here.
Data Analysis.1

The CBL-2 collected
absorbance data. By using
Beer’s Law we can conclude
that absorbance is directly
proportional to the
concentration of the Crystal
Violet indicator. Therefore
absorbance data can be treated
as concentration data.
Data Analysis.2

In order to determine the order of
the kinetics we need to evaluate
how the concentration of Crystal
Violet [CV] (absorbance data)
changed with respect to time.
Data Analysis.3

If the reaction is Zero Order
then a graph of [CV] vs. Time
will be linear.
It’s not
linear.
Data Analysis.5

If the reaction is First Order
then a graph of ln[CV] vs. Time
will be linear.
It’s Linear!
Data Analysis.6

If the reaction is Second Order
then a graph of 1/[CV] vs. Time
will be linear.
It’s not.
Conclusion




Summarize the lab procedures.
Give the result(s).
Determine source(s) of error.
Describe an error propagation.