Chemistry 345 May 11, 1999

Name ________________

1. A = 0.265; %T = ________.

2. A compound has a molar absorptivity of 9300 L/mol-cm at 395 nm. Calculate the molarity of a solution for this compound that has an absorbance of 0.425 when measured in a 1.00 cm cell.

3. At 415 nm a standard solution of iron that contains 4.87 mg of Fe per liter gives a %T of 15%. A 2.65 mg sample of an unknown iron sample is dissolved and eventually diluted to 0.500 liter. It gives a %T of 37% at this same wavelength. All samples were run in a 1 cm cuvet.

3a. What is the concentration of Fe in the unknown solution?

3b. What weight of Fe is present in the unknown solution?

3c What is the %Fe in the unknown sample?

Give the reason or rational for each of the following facts about IR absorptions.

4. The C-H stretch occurs at a higher frequency than the C-H bending frequency.

5. C-O stretch occurs at a lower frequency than the C=O stretch.

6. The OH is much more intense than the CH stretch in methanol.

7. The CO2 asymmetric stretch shows up in the IR but not the CO2 symmetric stretch.

8. The C-H stretch occurs at a higher frequency then the C-C stretch in ethane.