Sample pre-lab quiz for Identification of Two Unknown Compounds experiment.

1) Which of the following is a separation technique?

  1. column chromatography
  2. melting point determination
  3. NMR spectroscopy

2) Which separation technique would be the best method to separate benzoic acid (mp 115) and benzophenone (mp 50)?

  1. extraction
  2. distillation
  3. gas or column chromatography

3) A student has a mixture of two compounds and has determined by TLC that the solvent systems to separate these two are:

Solvent system 1, hexanes/ethyl acetate 6:1
Solvent system 2, hexanes/ethyl acetate 3:1

Solvent system 2 was used first on the column. Both compounds came off in the first 5 fractions. Then solvent system 1 was used, fractions 6-10 contained neither compound. Why?

  1. the student used the least polar solvent first
  2. the student used the most polar solvent first

4) Which compound below will have the highest Rf on a TLC plate?

5) Which of the two IRs below indicates a pure sample, assuming each compound has only one functional group?

    A


    B

Extra Credit: (Not extra credit, however, for 3381 students.)

How would you separate aniline from cyclohexanone by extraction?


  • dissolve in methylene chloride and extract the cyclohexanone into an aqueous layer by shaking with 3N NaOH.
  • dissolve in methylene chloride and extract the aniline into an aqueous layer by shaking with 3N NaOH.
  • dissolve in methylene chloride and extract the cyclohexanone into an aqueous layer by shaking with 3N HCl.
  • dissolve in methylene chloride and extract the aniline into an aqueous layer by shaking with 3N HCl.

    Answers to this quiz