Recrystallization - finding the amount of the final product of Cmpd A

  • #1

Homework Statement


Compound A
mass - 11.0g
solubility in ethanol at 78 deg C - 0.53 g/mL
solubility in ethanol at 0 deg C - 0.08 g/mL

Impurity B
mass - 2.5 g
solubility in ethanol at 78 deg C - 0.82 g/mL
solubility in ethanol at 0 deg C - 0.12 g/mL

Impurity C
mass - 2.5 g
solubility in ethanol at 78 deg C - insoluble
solubility in ethanol at 0 deg C - insoluble

The sample is recrystallized using 20mL of ethanol. It is boiled with 20mL of ethanol, filtered by gravity and then cooled in ice and filtered by suction. How much compound A should be obtained as the final product?


Homework Equations



Percent recovery = pure mass / crude mass x 100

The Attempt at a Solution



0.53 g/mL. 20 mL of ethanol. totals to 10.4 g.
2.5 g is insoluble due to Impurity C

Honestly, I do not know where to start as it feels like I am missing one piece of essential information.
 

Answers and Replies

  • #2
Borek
Mentor
28,628
3,102
0.53 g/mL. 20 mL of ethanol. totals to 10.4 g.
And that's almost the final answer. You should just take into account amount that was left dissolved in ethanol.

Mass of the recrystallized solid will be higher (because of the presence of B), but question doesn't ask for the mass of solid after recrystallization, but for the mass of compound A. Can be just a lousy wording though.
 
  • #3
10.4 g. The amount that was left dissolved in ethanol? Do you mean the 0.08 g? I'm not exactly sure what you're saying. Thanks for answering.
 
  • #4
Borek
Mentor
28,628
3,102
0.08 g per mL of ethanol - this is what is left in the solution after recrystallization (and it is lost with the ethanol that you are throwing out).
 

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