Sample pre-lab quiz for Thin Layer Chromatography and Melting Point Determination experiment.

1) If several compounds are present in a sample which is developed on a TLC plate, a column of spots is seen on the developed plate, with:

1. more polar compounds toward the top of the plate and less polar toward the bottom
2. more polar compounds toward the bottom of the plate and less polar toward the top
3. lower boiling compounds toward the bottom of the plate and higher boiling toward the top
4. lower boiling compounds toward the top of the plate and higher boiling toward the bottom

2) TLC is generally used as a qualitative analytical technique for:

1. determining the number of components in a mixture
2. checking the purity of a compound
3. following the course of a reaction
4. all of the above

3) In general, a compound will move further on a TLC plate with a:

1. non-polar solvent
2. polar solvent

4) Which of the following solvents is more polar?

1. ethyl acetate
2. hexanes

5) The melting point of a pure organic compound:

1. is broad, having a range of 3 degrees or more
2. is sharp, having a range of 1 degree or less
3. has a range of 5.5 degrees
4. varies according to atmospheric pressure

6) Calculate the Rf value for the following compound:

spot, 3.0 cm; solvent front, 10.0 cm

1. 3
2. 10
3. .3
4. 0

7) A beaker will be used as a "developing jar" in this experiment. When the TLC plate is set in this beaker, the solvent in the beaker must be:

1. above the pencil line used to guide the spotting of samples
2. deep enough to cover the entire TLC plate
3. deep enough to come about halfway up the TLC plate
4. below the pencil line used to guide the spotting of samples

8) Which of the following are flammable?

1. hexanes
2. ethyl acetate
3. ethanol
4. all of the above

Answers.