Deck 5: Drying Organic Solutions

Question 1

1 Which drying agents in Table 4.1 could be used to dry an ether solution of each of the following compounds?
(a) CH₃CH₂CH₂CH₂OH
(b) CH₃CH₂CH₂CH₂Br
(c) CH₃CH₂CO₂H
(d) CH₃CH₂CH₂CH₂NH₂

Answer 1

(a) MgSO₄, Na₂SO₄, CaSO₄, K₂CO₃
(b) any drying agent will be satisfactory
(c) MgSO₄, Na₂SO₄, CaSO₄
(d) MgSO₄, Na₂SO₄, K₂CO₃

Question 2

Why must a solid drying agent be removed from a solution before the solution is distilled?

Answer 2

The heat required for distillation will cause the hydrated crystals to dehydrate and recontami- nate the distilled sample with water.

Question 3

Because anhydrous sodium sulfate is a relatively inefficient drying agent, a student uses twice as much of this salt as recommended. What are the advantages and disadvantages of adding extra drying agent?

Answer 3

The principal advantage is that more water will be removed from the solution. The disadvan- tage is that more of the desired organic compound will be lost by adsorption onto the sodium sulfate crystals.

Question 4

A student adds too much drying agent to an organic solution and the organic solution is com- pletely covered by the drying agent. Explain how he or she can salvage the organic solution.

Question 5

A solution of an organic compound in diethyl ether is dried over sodium sulfate (Na₂SO₄). Why should the hydrated salts be removed by gravity filtration, and not the faster method of vacuum filtration?

Question 6

A solution of methylene chloride is dried by extracting with a solution of saturated sodium chloride solution, using a separatory funnel. When the two layers are allowed to separate, which layer will float to the top?