22. A series of organic solubility curves are shown below, for a variety of solv

Question

22. A series of organic solubility curves are shown below, for a variety of solvents. The y axis is amount of solvent per unit volume (mg/mL) and the x axis is degrees C. ACN 50 - Acetone 40 30 20 10 45 50 20 25 30 35 40 10 15 a. Which is the worst solvent for crystallization for this compound? (3) b. Justify your answer to part (a) in one sentence (3) Use the triangle solvent curve (Hac) to answer the following questions: I. How much of the solvent will be needed to dissolve 0.50 g of compound, at 50 °C? (4) Il. How much solute will remain in this solution when it is cooled to 10 °C? (4)

Explanation / Answer

From the solvent given in the graph, worst solvent is acetone, because in this compound is showing high solublity at all temperatures. So in this case, solvent requirment is less because the overall solublity of compound is higher but due to low slope of curve, recorvery of compound is very poor. For the good solvent test, firstly dissolve the compound at room temperature, if it dissolves then it is unsuitable for recrystallization.

At 50 degree celsius, amount of solvent is 40mg/ml i.e,

In 1 ml of solvent, 40 mg of solute is dissolved so for 0.50g

40 mg of solute = 1 ml of solvent

Convert grams into milligrams

0.5 X 1000 = 500 mg

0.50g or 500 mg = 1 / 40 X 500 = 12.5 ml of solvent

So to dissolve 0.50g of compound at 50 degree celsius we require, 12.5 ml of solvent.

When it is cooled at 10 degree celsius, then from the given graph we can observe it is approximately 15mg/ml

We have to calculate the percent recovery in this case which is calculated by

% recovery = Mass after recrystallization / Original mass X 100%

% recovery = 15 mg/ 40 mg X 100%

% recovery = 0.375 X 100 % = 37.5 %

From the percent recovery you get almost 37.5% of your compound and 62.5% of the compound remain in solution.

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