Investigation 11Crystal Violet Lab

Report
Investigation 11

Serial dilution




CV will stain skin and clothes
NaOH is a corrosive skin irritant
Wear goggles and aprons
Clean stained glassware with
isopropyl alcohol.

A) using wavelength of 540 nm
should result in an absorbance high
enough to provide an acceptable
range of absorbance values during
the reaction of CV and NaOH while
ensuring it is not too high to
interfere with reliability of the
instrument.
CV in micro M
Predicted absorbance
5
.26
10
.52
15
.78
20
1.04
25
1.30





Use dilution equation M1V1=M2V2
M1=25 microM
V1 is unknown
M2 is each desired final M specified in question
V2 is 10ml
CV in microM
Volume of CV
Volume of Water added
5
2
8
10
4
6
15
6
4
20
8
2
25
10
0


Absorbance should decrease because the
amount of a reactant like CV decreases over
time so more light passes through cuvette.
Note that by first calibrating / zeroing
instrument with blank cuvette the instrument
reads just the absorbance due to whatever
was not in the blank which in this case is the
CV



In 1:1 ration nothing is left of either and goes to
completion
In 1:1000 ration CV is limiting so none left.
Assume 1 mol of CV initial
CV
NaOH
I
1
1000
c
-1
-1
e
0
999



When the concentration of one chemical is
several orders of magnitude higher than
another its concentration hardly changes.
To within few sig figs we can assume it is
constant
So [NaOH]z is practically the same at the
beginning as at the end of rxn and can be
bundled in with k as new constant k*

Fill in the following table
Order with
Integrated
respect to CV rate law
Plot that is
linear
slope
Half life

For a total of 10mL combined volume the
following combination works well: 6mL
25microM CV with 4.00mL of 0.200M Na OH
and blank cuvette of 6mL of distilled water
combined with 4 mL of NaOH

Fig 3 shows three plots each for different chem
rxn. Looking at fig 3 one can see that the
reaction that is 0 order (blue) produces a
straight line for a graph concentration vs time.
The graphs for a different rxn which is first
order (red) and one for second( yellow) appear
to relatively linear until concentration dips
from starting value of 10M to roughly 1 or 2M

For quite a while all there follow linear
relationship. You have to collect data for a
sufficient amount of time. So don't collect data
for a set period of time. Instead collect until the
value of the absorbance of CV and its reaction
with NaOH has dropped to roughly 10%-20%
of initial value. At that point only 1 graph is
linear of those three different chemical
reactions.

http://www.chm.davidson.edu/vce/kinetics/
integratedratelaws.html


Typical cuvette ranges from 4mL to 6mL
You can make 10Ml of solution and pouring it
into cuvette


For the first reaction of CV with NaOH a blank
could be made from 6.00 mL distilled water +
4.00 mL 0.2M NaOH. This has everything but
CV to zero the absorbance reading
Then to perform actual rxn of CV and NaOH
combine 6mL 25.0micro M CV with 4 mL of
0.200 M NaOH
Concentration in Micro M
Predicted absorbance
12.5
0.742
10
0.639
7.5
0.508
5
0.332
2.5
0.159
Design the experiment to determine the kinetics of
candle burning. Some ideas that would influence the
kinetics are:
a)
Temp of air
b)
Different brands or types of wax
c)
Humidity of the air
d) Shape of one type of candle possibly modified via
whittling with kids scissors
e)
Length of the wick exposed
f)
Still air vs wind blowing (eg. Fan turned on a low
setting)

similar documents