Lab Reports - First Four Experiments
General comments on the lab reports.
You will do formal lab reports for two of the first four experiments (viscosity of
polyvinyl alcohol solutions, mutarotation of glucose) and informal lab reports for the
other two experiments (dipole moment of polar molecules in solution, 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...
"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. If you do things
differently than what is given in the lab manual 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 therory 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)
IMPORTANT:
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 cm3/g. When you use equn (7)
M = 7.6 x 104 []1.32 (which is actually MV)
DO NOT convert your value of [] into units of cm3/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.
________
In addition, 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).
1) What you are determining experimentally in this experiment is two things - 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.
2) There are two types of average molecular mass discussed in the lab report
Mv - volume averaged molecular mass
Mn - 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).
3) 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.
4) Your error discussion in this report will be less rigorous than in some of the
other lab reports.
5) 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).
6) 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.
7) 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 correct all of your observed rotations or the rotation observed for
water (which, since water is not optically active, should have been 0.0). Also remember
that you used 60% perchloric acid, and not 70% perchloric acid, and so need to take that
into account in calculating the concentration of H+ ion. Recall that perchloric acid is a
strong acid, so the concentration of perchloric acid is the same as the concentration of
hydrogen ion.
2) 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.
3) 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.
4) To find individual values for k1 and k-1 (the forward and reverse rate constants
you will use the following two relationships.
k = k1 + k-1 ,
where k is the overall rate constant for the reaction, found using eq. 8.
K = k1/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?).
5) Once you have obtained values for k, k1, 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.
6) Since finding a literature value for this reaction is difficult you are not required
to compare your results to the literature.
Dipole moment of polar molecules in solution. (informal lab report)
1) There are several changes between the procedure in the lab manual and the
procedure you use in this experiment.
Toluene is used as the solvent instead of benzene as a solvent
Solution density is calculated by using the density of toluene and the
chlorobenzene compound, and assuming no change in volume upon mixing.
A capacitance meter is used to measure the change in capacitance, instead of the
LC circuit described in the lab manual.
Measurements are done on chlorobenzene, 1,2-dichlorobenzene, and 1,3
dichlorobenzene.
2) The discussion of how to find the dipole moment from your experimental data
is a bit confusing, and so feel free to ask me questions. Note that you will have several
plots that need to appear in your report. In those plots the data for pure toluene can be
used as a data point. You will also need data on n (index of refraction) and  (density) to
find P02d, and from that, .
3) Because there is not a lot of data found for each compound, your error analysis
for this experiment will likely not be as rigorous as that given in other experiments.
4) Once you obtain values for the dipole moment for your three compounds, you
should use them to test the accuracy of the "vector model" for calculating dipole
moments in substituted benzenes. Assume the value for the dipole moment for
chlorobenzene is exact and represents a constant for a C - Cl bond. Then use this value to
calculated the values of dipole moment expected for 1,2 dichlorobenzene and 1,3
dichlorobenzene. Discuss how well your experimental values agree with the calculated
values, and in particular focus on possible explanations for any observed differences.
5) "Literature" values for the dipole moment for all of these molecules are given
in the CRC Handbook of Chemistry and Physics. These are not really literature values,
of course, since the CRC Handbook is a secondary source and not a primary source, but
you can use them anyway, since the primary literature is difficult to track down.
However, if you are adventurous, feel free to try and find real literature values for the
dipole moments for these molecules.
1) A table of information used in your data analysis.
Compound
M(g/mol)
(g/cm3)
n
toluene
chlorobenzene
1,2-dichlorobenzene
1,3-dichlorobenzene
XXX.XX
XXX.XX
XXX.XX
XXX.XX
X.XXX
X.XXX
X.XXX
X.XXX
X.XXX
X.XXX
X.XXX
X.XXX
Indicate where this information was obtained (CRC handbook, label of reagent bottle,
etc).
2) A table calculated densities and mole fractions.
compound: chlorobenzene
soln.
g
toluene
1%
2%
3%
4%
XX.XXX
XX.XXX
XX.XXX
XX.XXX
g
solute
mol
toluene
mol
solute

(g/cm3)
X(solute)
XX.XXX
XX.XXX
XX.XXX
XX.XXX
X.XXX
X.XXX
X.XXX
X.XXX
X.XXX
X.XXX
X.XXX
X.XXX
X.XXX
X.XXX
X.XXX
X.XXX
X.XXX
X.XXX
X.XXX
X.XXX
3) A table of raw experimental data. You will have data on air, toluene, and four
solutions for each of your three chlorinated benzene compounds.
compound: chlorobenzene
soln.
C(open)
pfarad
C(closed)
pfarad
C
pfarad
1%
XXX.X
XXX.X
XXX.X.
XXX.X
XXX.X
XXX.X
XXX.X
XXX.X
XXX.X
Average C
pfarad
XXX.X
4) The following plots:
 (dielectric constant) vs X(solute)
 (density) vs X(solute)
Note that pure toluene is a data point in all of your plots. Also note that since you
calculate density, the plot of  vs X(solute) should be a straight line with all of te data
points falling directly on the line
5) The calculation of P02d, P02, and from that, , for each compound.
6) A comparison of your experimental values for  with literature values (from
the CRC handbook).
7) A comparison of your results for 1,2- dichlorobenzene and 1,3-dichlorobenzene
to those expected from the "vector model". Show how the vector model results are
found. Note that if you do not have good experimental values for the dipole moments
you can use the literature values to test the vector model.
8) A brief discussion of sources of error in this experiment.
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 this equation uses log (that is log10) 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)
h (cm)
high (cm)
low (cm)
h (cm)
XX.X
XX.X
XX.X
XX.X
XX.X
XX.X
2) A table of calculated values for ln p and 1/T. Give the equation used to convert
p(N2) to T.
p(N2) 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.