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) Fro any solvent to be a good choice for crystallization is its ability to dissolve more at higher temperature and very less at lower temperature. In this case, solvent B has these two qualities. Based on the given data, the solubity at 100degC is 36 times more than that at 0 degC.

(b) Solubility at 100 degC is 5,5g in 100 ml of solvent B.

So, minimum amount at 100 degC for 2.11g of the crude will be 2.11*100/5.5 ml =38.36 ml rounded to 39 ml.

(c) Total recovery at 0 degC = 2.11-0.15 = 1.96 g

Ratio of impuity and crude product = 0.42/2.11 = 0.199

Impurity co-crystallized with pure compound = 1.96*0.199 g = 0.39 g.

Therefore, pure compound in the mixture = (1.96 -0.39) g = 1.57 g

So, purity of the recovered sample = 100*1.57/1.96 % = 80.10%

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