A solid substance D is soluble in ethanol to the extent of 2.6 mg / mL of ethano

Question

A solid substance D is soluble in ethanol to the extent of 2.6 mg / mL of ethanol at 25 C and 12.0 mg / mL of ethanol at 78 C. You have been provided with a sample that contains 40.0 mg of D and 5.0 mg of an impurity E. By showing all the calculation steps, describe how you would be able to purify D if E has the same solubility behavior as D in ethanol. Indicate the number of crystallization steps required to purify D, as well as the amount and percent recovery of pure D obtained after the crystallization steps have been completed.Show all calculations.

Explanation / Answer

Both the substance D and E has the same solubility behaviour.

Total amount of substance (D+E)= 40 mg + 5 mg= 45 mg

As we know that 12.0 mg is soluble in 1 ml of ethanol at 78 0C. In order to dissolve 45 mg of total substance requires 3.75 ml of ethanol at 78 0C. Upon cooling to 25 oC, 35.25 mg of the compound will precipitate and 9.75 mg stay in solution. (after first recrystallization)

Among 9.75 mg stay in solution, 5mg of impurity substance E and 4.75 mg of substance D are present in 3.75 ml of ethanol.

percent recovery of pure compound D= (amount of D precipitated/ total amount of substance) x 100

percent recovery of pure compound D= 78.33 %

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