Organic Chemistry Lab
Organic Chemistry Laboratory I (X36.1A)
For each question, write the letter of the correct answer in the column on the right :
|
1. Recrystallization is a laboratory procedure that is usually performed in order to-
A) increase the yield of the product of a reaction
B) separate enantiomers
C) determine whether a compound is polar or non-polar
D) increase the purity of the product of a reaction
E) lower the melting point of the product of a reaction
|
|
2. Why is benzene (C6H6, boiling pt. 78°C) not used as a recrystallization solvent?
A) because it is non-polar
B) because it is an aromatic compound
C) because its boiling point is too low
D) because it forms explosive peroxides
E) because it is toxic and an environmental hazard
|
|
3. Why is pentane (C5H12, boiling pt. 36°C) not used as a recrystallization solvent?
A) because it is non-polar
B) because it is an aromatic compound
C) because its boiling point is too low
D) because it forms explosive peroxides
E) because it is toxic and an environmental hazard
|
|
4. The most important reason for adding a boiling stick to a liquid before heating it is-
A) to prevent bumping (overheating) of the liquid
B) to stir the liquid while it is being heated
C) to prevent the liquid from boiling
D) to lower the boiling point of the liquid
E) to absorb impurities that are in the liquid on the surface of the wood
|
|
5. Norit® is the name of a company and of its main product, which is-
A) boiling sticks
B) activated charcoal
C) a solvent used for recrystallization
D) weighing paper
E) mother liquor
|
|
6. When you have a hot solution from which crystallization will occur, you should-
A) allow it to cool slowly and undisturbed
B) immediately cool it in an ice bath so that crystals will form rapidly
C) stir the solution vigorously with a stirring rod or boiling stick while it is cooling
D) place the solution under vacuum so that solvent will evaporate and crystals will form
E) add boiling chips to prevent “bumping” of the hot liquid
|
|
7. If the yield of crystals is small, a second crop of crystals can be obtained by-
A) adding more solvent
B) heating the solution to evaporate some of the solvent and then cooling
C) adding sand from the sand bath
D) adding activated charcoal
E) passing the solution through a Pasteur pipette containing glass-fiber filter paper
|
|
8. In a recrystallization procedure, the liquid that remains at the end of the procedure after the purified crystals have been removed from it is called the-
A) cosolvent B) distillate C) rinse D) mother liquor E) water bath
|
|
9. In the decolorization of brown sugar (Experiment 6, Part II), activated charcoal is removed by-
A) vacuum filtration
B) distillation
C) extraction with an acidic solvent
D) the glass-fiber Pasteur pipette method
E) centrifugation
|
|
10. A boiling stick must be added to a solution before the solution is heated because if a boiling stick is added to a hot solution-
A) the stick may dissolve in the solution
B) the stick may cause crystallization to occur prematurely
C) many bubbles may form quickly and the solution may froth and “bump”
D) the stick will absorb the substance that is being recrystallized
E) the stick will prevent crystallization from taking place
|