December, 1996



December, 1996 Chemistry 360 - Exam Dr. T. Smith-Palmer

[3] 1. Quantitative Analysis of two-component mixtures can be carried out by a variety of instrumental methods. You should be able to list at least six different instruments which could be used for this. Please list these 6. Choose three of these instruments. No more than one of these three should rely on sample atomization.

For each of these three instruments say [6] per instrument for a total of [18]

[1] (a) Type of component which can be analyzed (organic, inorganic, ion, solid, liquid etc.).

[1] (b) Give an example of a mixture which could be analyzed on the instrument.

[2] (c) Give the sample preparation (including any necessary additives) necessary for the sample described in (b).

[1] (d) What parameters are used to identify the sample components?

[1] (e) What parameters are used to quantify the sample components?

2. In FT Infrared spectroscopy, we look at the absorbance of light as a function of wavenumber.

In UV-visible absorption spectroscopy, we look at the absorbance of light as a function of wavelength.

The instruments we use, however, are quite different.

[2] (a) What λ region are we dealing with in each case?

[2] (b) What kind of molecular interaction with light?

[2] (c) What kinds of light source for each?

[2] (d) What kinds of λ selector?

[6] (e) Choose one of the λ selectors mentioned in (d) and describe in detail what it consists of and how it operates. Include a diagram of the light path.

[2] (f) Name two detectors which might be used in an FTIR.

[5] (g) Describe one of the detectors named in (f).

[3] (h) What are the advantages of FTIR compared to the older dispersion method of IR.

3. (a) Flames, furnaces and plasmas are used as atomization sources. For each

[1.5] - Note typical temperature

[4.5] - What is measured and how?

[6] - Advantage and disadvantage

[5] (b) Describe either Zeeman or Hieftje background connection.

[12] 4. Do 2 of I, II and III. (Each is worth 6)

(I) (a) Dansyl chloride has an absorption maximum at 335nm and fluoresces at 516nm. Explain the following fluorescence emission spectrum (a) and excitation spectrum (b).

(b) Where (at what wavelength) would you expect to see the Raman band for H2O (O-H stretch) in spectrum (a)?

(II) (a) What differences in the IR spectra of the following pairs of compounds would allow you to distinguish between them?

O O

(a) CH3CH2C and CH3CH2C

OH H

(b) CH3CH2NH2 and CH3CH2NHCH3

(c) CH3CH2 = CH2 and

(d) CH3(CH2)4CH3 and

(b) The IR spectra of three compounds are shown below. Determine the functional group in each of the compounds. Briefly explain.

(III) (a) Two 1H nmr spectra and the structures of three compounds are given below. For each spectrum below, find the matching structure. Justify your choice. (Spectras not available)

Possible structures: (a) Cl2CHCH3

(b) Cl3CCH2CHCl2

O

(c) CH3 - C

O - CH2CH3

b) What ideal slope would you expect for the following ion selective electrodes:

Ca2+ ; Ag+ ; F-

(c) Calculate the thermodynamic potential for the cell

Ag/Ag+(0.200 M)(Cu2+(0.100 M)(Cu

and indicate whether it is galvanic or electrolytic.

E(Ag+ = 0.799 V E(Cu2+ = 0.337 V

[15] 5. Write notes on 5 of the following:

(a) Photodiode arrays

(b) Why is differential pulse polarography more sensitive than dc sampled polarography.

(c) What is the purpose of a supporting electrolyte in polarography?

(d) What is a junction potential? Include an example of a ‘good' salt for use in salt bridges.

(e) Differences between Fluorescence and Phosphorescence.

(f) Determination of the speciation of chromium in water.

(g) Extraction - Spectrophotometric determination of Cobalt in soils and plants.

(h) Applications of Near I.R. spectroscopy

[6] 6. Do either (a) or (b)

(a) Describe how a laser works.

OR

(b) Discuss how concentration and activation over potentials arise, and what factors affect the size of overpotentials.

[4] 7. You are working in a lab where the following analyses are being carried out. You are being asked to recommend the purchase of an instrument upgrade, an add-on or a new instrument entirely, in order to lower the LOD.

Say what you would recommend for each of the following cases. Don't just say ‘upgrade' or ‘new instrument' - say what the upgrade or new instrument should be. (e.g. "add a headspace system to the gc.")

(a) Mercury is being analyzed by Flame AA.

(b) Cadmium is being analyzed by classical wave polarography.

(c) Zinc is being analyzed by Flame AA.

(d) Quinine is being analyzed by UV absorption at 250 nm.

[1] 8. How could you lower the LOD for an nmr or FTIR experiment?

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