1. Crystal Violet Lab
Investigation 11

2. Prior to lab review:
Serial dilution

3. Safety CV will stain skin and clothes
NaOH is a corrosive skin irritant
Wear goggles and aprons
Clean stained glassware with isopropyl alcohol.

4. Prelab 1
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.

5. 1b Your xs should be at the absorbance values given by the equation A=(abs from Fig 1 at chosen wavelength)*(diluted conc of CV)/(stock conc of CV)
CV in micro M
Predicted absorbance 5
.26 10
.52 15
.78 20
1.04 25
1.30

6. 2 Use dilution equation M1V1=M2V2 M1=25 microM V1 is unknown
M2 is each desired final M specified in question
V2 is 10ml

7. CV in microM
Volume of CV
Volume of Water added 5 2 8 10 4 6 15 20 25

8. 3
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

9. 4a 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 e
999

10. 4b
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*

11. 5. Graph 3 plots to test 0, 1 or 2 order
Fill in the following table
Order with respect to CV
Integrated rate law
Plot that is linear
slope
Half life

12. 6
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

13. Skip 7

14. 8a
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

15. 8b
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.

16. Simulation on Integrated Rate Law

17. Procedure Typical cuvette ranges from 4mL to 6mL
You can make 10Ml of solution and pouring it into cuvette

18. For the first reaction of CV with NaOH a blank could be made from 6
For the first reaction of CV with NaOH a blank could be made from 6.00 mL distilled water 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 M NaOH

19. Calibration curve sample data for CV
Concentration in Micro M
Predicted absorbance
12.5
0.742 10
0.639
7.5
0.508 5
0.332
2.5
0.159

21. Extension activity-write this after your lab conclusion
Design the experiment to determine the kinetics of candle burning. Some ideas that would influence the kinetics are:
Temp of air
Different brands or types of wax
Humidity of the air
Shape of one type of candle possibly modified via whittling with kids scissors
Length of the wick exposed
Still air vs wind blowing (eg. Fan turned on a low setting)