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RECRYSTALLIZATION Pre Lab Questions 1. Complete the following table: Compound Structure Solubility in Hot Water Solubility...

RECRYSTALLIZATION

Pre Lab Questions

1. Complete the following table:

Compound

Structure

Solubility in Hot Water

Solubility in Cold Water

Acetanilide

Sugar

2. What is the literature (known) melting point for acetanilide?

3. A student performed a recrystallization to purify a crude sample from a reaction. The amount of crude material collected from the reaction was 13.56 grams. After the purification, the student collected 8.97 grams of extremely pure material.

a. What is the percent recovery of the desired material?

b. Is it possible to determine how much of the desired material

remained in solution after the filtration?

4. The solubility of acetanilide in hot water is 5.5 g / 100 mL at 100oC and its solubility in cold water is 0.53 g / 100 mL at 0oC. What would be the maximum theoretical percent recovery from the crystallization of 2.5 g of acetanilide from 50 mL of water? Show the calculation.

Homework Answers

Answer #1

Answer 3: a) Since 8.97g of sample is recovered from 13.56 g crude,

% recovery would be = 8.97x100/13.56 = 66.15 %

b) Yes, 13.56 - 8.97 = 4.59 g material is there in the solution after filtration.

Answer 4: Since solubility of acitanilide at 100 C is 5.5 g /100 mL at high temperature,

Hence, 2.5 g acitanilide would be completely soluble in 50 mL water at high temperature.

At low temparature, 0.53g/100mL == 0.265 g/50 mL would not be recoverable after crystallization at low temperature.

Hence, theoretical recovery would be: 2.5 - 0.265 = 2.235 g.

Hence %recovery = 2.235/2.5 x100= 89.4 %

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