I have had a number of questions concerning what is expected in the last set of lab reports. I expanded on the questions in the text in my pre-lab announcements, but that tends to get lost in the noise. There are two things I would like you to do that I did not tell you to do. I list them below and offer "EXTRA CREDIT" for your answers.
Please follow the form for the reports as requested. I like the reports boring (just the facts and interpretations of the facts -- no feelings or fiction allowed) and easy to read.
Here is an attempt at clarification:
Page 23 indicates (and I believe I also said in pre-lab) that, during the day the orange and purple complexes were made, you were to:
1. Keep a record of your observations, quantities of reagents and procedure on data sheets.
2. Do not submit a separate report for Experiment 6.
3. Discuss both complexes in the report for Experiment 7, as prescribed in the handout for Experiment 7.
If you did not do this, you may wish to communicate with your partner to get some idea of the color changes, bubble formation, etc. at various stages of the preparation.
+++++++++++++++++++++
Page 27 states:
Report for Experiments 6 and 7
The DATA section of the report should include a report on the synthesis of both complexes, including observations of color changes and mass yields, and a table of the titration data for your complex.
====
I take the above to mean the color changes and mass yields for both complexes.
EXTRA CREDIT will be given for rational attempts to write balanced equations for any and all steps wherein a reaction occured as noted by color change or bubbling, etc.
The table of titration data is just for your complex.
++++++++++++++++++
Page 27 also states
The CALCULATION section of the report should include a clear sample calculation of the equivalent weight of the complex.
The RESULTS section of your report should include all your values of the equivalent weight of your complex, a discussion of how you determine your "best " value of the equivalent weight of your complex, and a justification for rejection of any of your results.
=================
I read this to include an estimate of the error (get used to it, you will need to do it all of the time in CHEM231). This means propagation of error starting with the uncertainty (estimated error or standard deviation) on the molarity of the base and including error estimates on EVERY measurement made to get to the equivalent weight. This should be compared with the estimated error based on the replicate titrations. Then use the larger of the two values of uncertainty for the equivalent weight should then be propagated to the formula weight. If you used the Q-test, say so and what you did in response to it.
++++++++++++++++++++
Page 27 also states
The CONCLUSION section of your report should discuss the meaning of your results and a prediction of the formula of your product.
Question
This question explores the use of the technique you used in this experiment to analyze a sample of an ionic compound. A 2.4265 g sample containing aluminum perchlorate and various non-ionic organic substances is dissolved to make 250.00 mL of solution. A 50.00 mL aliquot is passed through a hydrogen-form cation exchange resin, and the effluent is titrated with 18.32 mL of 0.1046 M NaOH. Calculate the percentage of aluminum perchlorate in the sample.
++++++++++++++++++++++++++++++++
Page 30 states
Report, Part I
1. Convert your %T data to A using the relationship shown below.
A = log10[100 / %T] A = absorbance
%T = percent transmittance
log10 = logarithm to the base 10
Make a plot of A vs. wavelength from 350 to 600 nm. This is called an absorption spectrum. Make sure to properly label your axes.
2. Compare the spectrum you measured with that of your partner who measured the other complex. How do the two spectra differ? Explain the possible causes of any differences observed. Report the energy, in wavenumbers (cm-1), of the light that causes the maximum absorbance in each complex. Include both spectra with your report; therefore, partners must make copies for each other.
+++++++++++++++++
In pre-lab I asked that you also include lamda max and the absorption coefficient (extinction coefficient) for each and to indicate how the absorption coefficient (extinction coefficient) "fits" with the generalizations about this term given as a hand-out in the pre-lab. EXTRA CREDIT will be given for also calculating the energy of the transition.
++++++++++++++++
Page 31 states
Report, Part II
1. From the spectrum, predict the color you would expect each of the five solutions to have and identify the solution, which you think matches the spectrum.
2. Calculate the energy, in cm-1, corresponding to the absorption maximum in each spectrum.
3. Determine the oxidation state of the transition metal in each compound, and indicate the number of d electrons the metal has.
===================
I asked that you compare the intensities of the colors with the general observations about absorption coefficients (extinction coefficients). Specifically, why is the deep purple complex so intense (high extinction coefficient) while the orange, red, blue and green complexes were rather pale?
++++++++++++++++
Page 32 states
Report, Part III
Arrange the 8 complexes above in order of increasing energy of their lowest energy electronic transition. Account for the changes in the composition of the complex ions that would cause the difference in transition energy.
===========
This is NOT a matching problem. It starts as merely a sorting problem. The complexes have absorbances at the energy given on the same line. You accounting for the changes should reflect all information you have been given on the energy separation for octahedral complexes.