4. You carry out a synthesis in lab and obtain 2.11 g of a crude product. You de

Question

4. You carry out a synthesis in lab and obtain 2.11 g of a crude product. You decide to purify your crude product with Solvent B although you have other solvents (Solvent A and Solvent C) available in the lab as well. The solubility of your crude product in all of the solvents is given in the table on the following page Temp Solvent A Solvent B Solvent C 100 mL 0.10 0.15 0.20 0.25 0.30 0.40 100 mL 0.15 0.30 0.60 1.20 2.70 5.50 100 mL 5.00 5.20 5.40 5.60 5.80 6.00 0 20 40 60 80 100 What TWO qualities make Solvent B a good choice for purifying your crude product? What is the minimum amount of hot Solvent B at 100°C that you can use to dissolve your crude product? It turns out that 0.42 g of your crude product is an impurity and that the impurity has the same solubility as the desired product in Solvent B. What is the percent purity after your recrystallization at 100°C and 0°C using a minimum amount of Solvent B? a. b. c.

Explanation / Answer

(a)(i) The crude product is nearly insoluble in the solvent B at room temperature

(ii)The solubility is gradually increasing with temperature, so that at the boiling temperature of the solvent B, the crude product is highly soluble.

(b)100ml of solvent B dissolves 5.50g crude product at 1000C.So we need to know the minimum amount of solvent B which dissolves 2.11g of crude product at 1000C

5.50g X x ml = 2.11g X 100ml

x = (2.11g X 100ml)/5.50g = 38.36ml

(c) Amount of crude product = 2.11g

Amount of impurity = 0.42g

Amount of pure product = 2.11-0.42 = 1.69g

At 1000C, 2.11 g of crude product needs 38.36ml of solvent B.Here the crude product contain 1.69g of pure product and 0.42 g of impurity.Hence the recrystallization will crystallize 1.69g of pure product and 0.42 g of impurity.

Percentage purity of the product = (1.69/2.11) X 100=80.09%

Similarly, at 00C, 2.11g of crude product needs minimum 1406ml[ x = (2.11g X 100)/0.15 = 1406ml] of solvent B to dissolve completely.Here also the recrystallization will crystallize 1.69g of pure product and 0.42 g of impurity.

Hence the percentage purity of the product at 00C= (1.69/2.11) X 100=80.09%

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