Lab Reports - First Four Experiments
General comments on the lab reports.
You will do formal lab reports for three of the first four experiments (viscosity of polyvinyl alcohol solutions, mutarotation of glucose, bromination of acetone) and an informal lab report for the other experiment (lattice energy of argon). In both the formal and informal lab reports be sure to list the names of all of your lab partners.
Formal lab reports .
The formal lab reports should use the format given below.
1) Abstract - A summary of the main results from your experiment.
2) Introduction - This should be a general discussion of the purpose of the experiment and background information concerning the theory behind the experiment. This should be relatively brief (a few pages). Try not to simply regurgitate the information in the lab manual, but put it in your own words. You can of course refer to the lab manual and cite it as a reference.
3) Experimental method - This will usually be a very short section. If you follow the procedure in the lab manual all you really have to say is something like the following.
"The experimental procedure used in this experiment is that given in Garland et al. [1]." where [1] is a reference to the relevant section of the lab manual or to the handout for the experiment. If you do things differently than what is given in the lab manual or handout this should be included.
4) Results - You should begin with your raw data and end with your final results. You should show step by step how you go from the experimental results to the values for the things you are finding in the experiment. Sample calculations are often useful in explaining how the data analysis was done. Tables and figures, particularly when well organized, are also often of use here.
5) Discussion - Here you do several things. You discuss the significance of your results.
What do they mean? Are they consistent or inconsistent with what theory or with literature values (when those are available). You should also expand on your discussion of error in this section of the report. Your results section should have estimates of experimental error, usually based on scatter in the data. In the discussion section you should think about what the main sources of error in the experiment are and try to estimate their approximate magnitude. Are the expected errors about the same size as the errors actually observed? If not, why not?

6) References - This should be a list of references used in the body of the report. This will likely include the lab manual. It may include Atkins if you use that as a source for the discussion of the experiment in the introduction. It should also include the source(s) for any literature values you use.
7) Appendix - You will likely have an appendix containing the raw data from your experiment. You occasionally might want to include an additional appendix with other useful information.
Informal lab reports .
Instructions for the informal lab reports are given below following the discussion of the experiment.
Experiments - In this section I am pointing out a few important things about each experiment. This is not meant to be an exhaustive list of things to do in the report, but a guide to some of the things that you should think about or that should be there. It will also mention those things in the lab manual you can ignore.
Viscosity of polyvinyl alcohol solutions. (formal lab report)
1) The book suggests preparing a third solution with concentration equal to 1/4 th of the initial concentration. DO NOT DO THIS. Because the elapsed time for this solution for the cleaved polymer will be close to that for pure water, any small errors in this measurement will bias your data for the cleaved polymer. It is better to simply do the two solutions that are required (initial and
1
/
2
initial).
2) In your calculations of average molecular mass, the value of [

], the intrinsic viscosity, is given in units of 100 cm
3
/g. When you use equn (7)
M = 7.6 x 10 4 [

] 1.32
(which is actually M
V
)
DO NOT convert your value of [

] into units of cm
3
/g. As a check, the experimental values for [

] used in equn (7) usually fall within the range 0.05 < [

] < 1.5. If your value falls outside this range check with me.
3) It is important to use the same volume of solution in each measurement of viscosity. For the viscometers we have in the lab, a 10.00 mL sample should be used
(delivered by volumetric pipette).
4) Be sure to rinse out all glassware containing uncleaved or cleaved polymer solution immediately after use, particularly the viscometer. If polymer deposits out of solution it is extremely difficult to remove. For the viscometer, you should flush the narrow diameter tube of the viscometer several times with deionized water, by using a pipette bulb to suction water through the tube.

5) You are determining two things in this experiment in this experiment - the average molecular mass of your polymer before cleavage and the average molecular mass after cleavage. By knowing these numbers, there are several additional things you will be able to find, including
- the average number of monomers per polymer, both before and after cleavage
- the average number of places per polymer molecule where cleavage occurs
- the number of reverse linkages (and therefore the percentage of reverse linkages) per polymer molecule.
You are able to find the number and percent of reverse linkages per polymer molecule because cleavage only occurs at the site of a reverse linkage.
6) There are two types of average molecular mass discussed in the lab report
M v
- volume averaged molecular mass
M n
- number averaged molecular mass
Do your calculations for both of these. The results will be similar (if not, you are likely doing something wrong in the calculations).
7) The discussion of how your experimental results are related to the average molecular mass of the uncleaved and cleaved polymer is a bit confusing, so feel free to ask me questions. If you go through the discussion slowly you can probably figure out what Garland et al. are trying to say.
8) Your error discussion in this report will be less rigorous than in some of the other lab reports.
9) In the calculations section of the lab manual values for the viscosity of water are given at 23

C, 25

C, and 27

C. You can use your observed value for temperature to interpolate (or extrapolate if outside the temperature range 23

C - 27

C) the appropriate value for viscosity to use in finding the apparatus constant B for your viscometer (eq. 3).
10) Since the values for average molecular mass for the uncleaved and cleaved polymer are unique to this particular batch of polymer, there are no literature values to compare to.
11) You do not have to answer the questions given in the discussion section of the lab manual.

Glucose (handout). (formal lab report)
1) Remember to save the four solutions used in your measurements for optical rotation so that “infinite time” rotations can be obtained. I will measure these for you at least 12 hours after the end of the lab, which is sufficient tie for the system to come to equilibrium. You can obtain the infinite time rotations from me in class or e-mail me for their values.
1) If you used 60% perchloric acid, instead of 70% perchloric acid you need to take that into account in calculating the concentration of H
+
ion. Perchloric acid is a strong acid, so the concentration of hydrogen ion is the same as the concentration of perchloric acid.
3) Since the observed rotation is proportional to the specific rotation in the experiment (eq. 1) you can use eq. 8, with the observed rotations, to find the value for k, the overall rate constant for the mutarotation reaction. It is most convenient to do the calculations in eq. 8 on a spreadsheet (such as with EXCEL), although you are free to do them by hand if you wish.
4) Notice that eq. 8 makes use of the difference in observed rotations. Therefore, in using eq. 8 it doesn't matter if you use the corrected or uncorrected rotations, since the correction factor will cancel out. You should be able to not only get a value for k for each run, but an estimate for the error in k at the 95% confidence limits.
5) To find individual values for k
1
and k
-1
(the forward and reverse rate constants you will use the following two relationships. k = k
1
+ k
-1
,
where k is the overall rate constant for the reaction, found using eq. 8.
K = k
1
/k
-1
,
where K is the equilibrium constant for the reaction, found using eq. 5.
Note that to find K you will need to use the corrected rotations. You can estimate the error in the value for K based on the fact that K should be the same in all four runs
(why?).
6) Once you have obtained values for k, k
1
, and k
-1
, you will want to discuss how the rate constants for the reaction depend on hydrogen ion concentration. Depending on the quality of your data you may end up with only a qualitative statement (the rate generally increases with increasing H
+
concentration) or you may be able to say something more quantitative.
7) Since finding a literature value for this reaction is difficult you are not required to compare your results to the literature.

Bromination of acetone (handout). (formal lab report)
1) You should use your data to not only find values for p and q (reaction orders) but the 95% confidence limits for these values. Your values for p and q should be rounded off to the nearest integer values before you find values for k (rate constant) from your experimental data. You should report both the average value for k and the 95% confidence limits on the value for k, in appropriate units. You may express time in either seconds or minutes, whichever is most convenient.
2) While you can obtain values for dA/dt from the hard copy of the plots of absorbance vs time, you can also do this using the files of your experimental data, which are in a format appropriate for use in Excel. If you want copies of the data files e-mail me, and I will send them to you. They will require minor editing before use.
3) You do not have to compare your results for p, q, and k with literature values, as it is difficult to find values for these in the literature (because this reaction was first investigated nearly a century ago!).
Lattice energy of argon. (informal lab report)
1) The main thing you are determining experimentally is

H
 sub
, the enthalpy of sublimation of argon. You can do this from a plot of ln p vs 1/T, where p is the vapor pressure of argon and T is the absolute temperature (in K), obtained from your measurements of the vapor pressure of liquid nitrogen in the apparatus and eq. 12b. Note that equation 12b is in terms of log (that is log
10
) and not ln.
2) You can find the enthalpy of sublimation using eq. 13, which is really the following equation ln p = - (1/T) (

H
 sub
/R) + C , where R, the gas constant, is in energy units (J/mol .
K) and C is a constant.
By plotting ln p vs 1/T you should be able to find the value for

H
 sub
, and also the 95% confidence limits on that value. This error will of course propagate when you calculate the lattice energy for argon (eq. 8).
3) Compare your value for lattice energy to that calculated from eq. 11, which applies for a face-centered cubic lattice, the expected crystal structure. Comment on the agreement (or lack of agreement) between your experimental and calculated value for lattice energy.
4) You can ignore all of the discussion on "second law" and "third law" corrections for

H
 sub
, as your data is unlikely to be sufficiently precise to justify these calculations. We are going to assume your experimental value for the enthalpy of sublimation is, to within experimental error, the same as

H
 sub
.

5) There are literature values for

H
 sub
, though they are difficult to find. Values are reported in the following references.
Clark, A. M., F. Din, J. Robb, A. Michels, T. Wassenaar, Th. Zwietering, (1951).
Physica, 17, 876-884. (

H
 sub
= 7750. J/mol)
Flubacher, P., A. J. Leadbetter, J. A. Morrison, (1961). Proc. Philo. Soc. London,
78, 1449-1461. (

H
 sub
= 7730.

20. J/mol)
The informal lab report should be organized as follows:
1) A table of the raw experimental data. (Note: - Be careful in calculating
 h, since the two manometers use a different scale to indicate height.). atmospheric pressure = XXX torr
Nitrogen Argon high (cm) low (cm)
XX.X XX.X
 h (cm)
XX.X high (cm)
XX.X low (cm)
XX.X
 h (cm)
XX.X
2) A table of calculated values for ln p and 1/T. Give the equation used to convert p(N
2
) to T. p(N
2
) torr T (K) 1/T (K
-1
) p(Ar) torr ln p(Ar)
XXX. XX.XX X.XXXXX XXX. X.XXX
3) A plot of ln p vs 1/T.
4) A calculation section including the value for slope found from your plot of ln p vs 1/T (with correct units and the 95% confidence limits). From the slope, you should then calculate

H
 sub
(with correct units and the 95% confidence limits), and the lattice energy (with correct units and the 95% confidence limits). Compare your experimental value for

H
 sub
with literature values, and your value for the lattice energy with the
"theoretical" value expected for a face centered cubic lattice (and show how you obtain this "theoretical" value for lattice energy).
5) Also include a brief error analysis indicating the main sources of experimental error and their approximate magnitude.