Separations and Purifications

Question 1

For an extraction, what is the solvent for the organic phase and the aqueous phase?

Answer 1

The solvent for the organic phase is a nonpolar solvent that dissolves other nonpolar solutes. The solvent for the aqueous phase is water that dissolves ionic and polar solutes.

Question 2

In distillation, what properties are being exploited and which of those two properties are collected?

Answer 2

Separates liquids based on boiling point. The stuff with the lower boiling point is boiled off and collected; the higher boiling point stuff remains behind.

Question 3

What is the difference between simple and fractional distillation?

Answer 3

Simple distillation = done with a normal column = can separate two liquids if the difference in boiling point is large.

Fractional distillation = done with a fractionating column = can separate two liquids with smaller differences in boiling point.

Question 4

What is vascuum distillation?

Answer 4

done under lower pressure (vacuum) = lowers the boiling point for all liquid components so you don’t have to crank up the temperature so high (chemical might decompose).

Question 5

Describe what occurs with gas-liquid chromatography

Answer 5

• The gas part is the mobile phase, the liquid part is the stationary phase coated to the inside walls of the column.
• Substrate equilibrates between mobile (gas) and stationary (liquid coat) phase.
• Those with greater affinity for the stationary phase comes out of the column slower.
• Polar substrate has more affinity for polar stationary phase, and hydrophobic substrate has more affinity for hydrophobic stationary phase.

Question 6

Describe what occurs with paper chromatography.

Answer 6

• Solvent = mobile phase.
• Paper = stationary phase.
• Pigments in dyes stick to paper, solvent tries to wash them along, those with greater affinity to paper stays behind, those with greater affinity to solvent gets washed along. So like-molecules move slower.

Question 7

What is the difference between thin-layer chromatography and paper chromatography?

Answer 7

• Thin-layer chromatography = advanced paper chromatography.
• Instead of paper, you have a plate coated with a specific stationary phase of your choosing.

Question 8

Why is recrystallization performed?

Answer 8

Recrystalization = barely dissolving your compound, then let it recrystalize out of solution = compound ends up being more pure.

Question 9

What is a good solvent choice for recrystallization?

Answer 9

choose a solvent in which your compound is soluble in at warm temperature, but not at cool temperature. Also, choose a solvent in which impurities are highly soluble.