Sample pre-lab quiz for Thin Layer Chromatography I (3361) experiment.

1) If two substances are run on the same TLC plate have the same Rf value, they are:

  1. likely, but not necessarily, the same compound
  2. definitely the same compound
  3. likely, but not necessarily, different compounds
  4. definitely different compounds

2) Which of the following solvent mixtures is more polar?

  1. ethyl acetate/hexanes 50:50
  2. ethyl acetate/hexanes 80:20

3) Which of the following methods can be used to visualize the spots on a developed TLC plate?

  1. an ultraviolet (UV) lamp
  2. iodine (I2) crystals in a jar
  3. heating the plate to high temperature
  4. spraying the plate with a reagent
  5. visualization by the color of the compound
  6. all of the above

4) The TLC plate is prepared by drawing a light line 1 cm from the bottom of the plate to mark where the pain relievers should be spotted. This line is drawn with:

  1. a pencil
  2. a black pen
  3. a blue pen
  4. a red pen

5) The three compounds below are run on a silica gel TLC plate developed in hexanes-ethyl acetate (70:30).

  1. the carboxylic acid will run the fastest and the aromatic the slowest
  2. the carboxylic acid will run the fastest and the alcohol the slowest
  3. the aromatic will run the fastest and the carboxylic acid the slowest
  4. the alcohol will run the fastest and the aromatic the slowest

Consider the following TLC plate when answering questions (6) and (7). The plate was developed in hexanes.

6) The Rf of Compound C is:

  1. 10
  2. 8
  3. 5
  4. 3.5
  5. 0

7) A fresh TLC plate is spotted with compounds A, B, and C, but this time the solvent is methylene chloride. How will this affect the Rf of compound A?

  1. the Rf of A in the new solvent will be the same as in hexanes
  2. the Rf of A in the new solvent will be greater than that in hexanes
  3. the Rf of A in the new solvent will be less than that in hexanes

Answers.