Question

RECRYSTALLIZATION



An impure sample of compund A is contaminated with two impurtities B and C. The sample is to be purified by recystallization using ethanol as solvent. The solubility properties of the three components are summarized below.

compound A: solubility in ethanol at ~78 deg celcius = 0.53g/mL. solubility in ehtanol at 0 deg celcius = 0/8g/mL
Impurity B: solubility in ethanol at ~78 deg celcius = 0/86g/mL. solubility in ethanol at ~0 deg celcius=0.12g/mL
Impurity C: insoluable in ethanol at both temperatures.



The impure sample contains11.0g of compound A, contaminated with 2.5g of B and 2.5g of C and is recrystallized using 20ml of ethanol. The sample is boiled with 20mL of ethanol, filted by gravity and then cooled in ice and filtered by suction. How much of compund A should be obtained as the final product? Will the sample be contaminated with any of the impurtities? Explain (using calculations to support your answer)

Answer 1

If you melt the sample in a solvent or water, and recrystallize it, there are always going to be impurities, but probably in a lower yield. You can always check by checking it's melting point in a machine and compare to the literature value. That's a fairly broad way to check.