Chemistry 422 Exam III


December 4, 1998  

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Instructions: Read the whole exam before starting to work on individual problems; work those that you find the easiest first. Budget you time!

a. What are shims in a NMR spectrometer, and what is their purpose?

Why is there no observed splitting between carbons in 13C spectra?

Draw a diagram of the major components of a NMR.

Calculate the relative number of protons (g = 2.68x108T- 1s- 1) in the higher and lower magnetic states when a sample is placed in a 7.00-T field at 20.0C.


a-c see notes

d. Use the simplified form of the Boltzmann equation:


a. Draw a diagram of the major components of the electron impact ionization part of a mass spectrometer.

b. Explain why a vacuum is required in mass spectrometry.

The time of flight of a molecule having a molecular mass of 50.0 g/mol in a mass spectrometer after being accelerated with 2000 V was 5.00 ms. What would the time be for a molecule with a molecular mass of 75.0 g/mol after being accelerated with 2500 V?


3. Determine the Ksp of Ag2CrO4(s) at 298K using the information given below.

Ag+(aq)+ e-

Ag(s) Eo = +0.799 V

Ag2CrO4(s) + 2 e-

2Ag(s) + Eo = +0.446 V



2Ag+(aq)+ 2e- Eo = - 0.799 V

Ag2CrO4(s) + 2 e-

2Ag(s) + Eo = +0.446 V


2Ag+(aq) +

4. Determine the length of time (s) it would take to reduce the concentration of iron from 0.0200 M to 0.00500 M. Use graph below (left).


5. a.Determine the number of electrons involved in the reduction from the polarographic wave shown in the graph on the right. Process is everything here! No points will be given for a correct answer without showing the work!

b. Draw a diagram of the major components of a polarograph and explain the principles of its operation.

Solution: id = 5.0, E1/2 = - 0.40 V; E1 = - 0.375, i1 = 0.62 n = 2.

6. Determine the number of theoretical plates and the height equivalent of a theoretical plate using the graph to the right and given that the column was 30.0 cm long.

Solution: Use the normal equation for theoretical plates. The width of the peak is 0.5 and gives a total of 11, 000 theoretical plates with H = 2.78x10- 3 cm