Re-crystallization Lab

Question 1

What is the structure of Acetanilide?

Answer 1

CH3 bound to C which is double bonded to O and single bonded to NH, where the NH is single bonded to a benzene ring

Question 2

What is the structure of dichloromethane?

Answer 2

CH2Cl2

Question 3

What is the structure of ethanol?

Answer 3

CH3CH2OH

Question 4

What is the structure of petroleum ether?

Answer 4

Hexane

Question 5

What is the structure of acetone

Answer 5

Three carbons single bonded to each other, middle one is double bonded to O

Question 6

What is the structure of water?

Answer 6

H2O

Question 7

What are some common solvent selection criteria? (4)

Answer 7

The compound being purified must be insoluble in the solvent at RT. The compound should be soluble in boiling solvent. The solvent BP must be lower than the compound MP. Abundant crystals should be recoverable from cool solvent.

Question 8

Describe oiling out

Answer 8

If the compound is above its MP when it begins to separate from solution, it forms a molten “oil” phase rather than crystals. The ‘oil’ frequently refuses to form crystals after cooling to RT or ice bath, due to trapped solvent. However, a seed crystal of the pure compound sometimes initiates crystallization.