Question

In: Chemistry

A chemist decided to try and recrystallize (purify) quinidine from acetone solvent. The solubility of quinidine...

A chemist decided to try and recrystallize (purify) quinidine from acetone solvent. The solubility of quinidine in acetone is 1.0 g dissolves in 3.0 mL of hot acetone and 100 mg dissolves in 1.0 mL of cold acetone. If he started with 0.35 g impure quinidine, what is the minimum amount of solvent he should use to recrystallize the impure solid? Is acetone a good choice of solvent?

Solutions

Expert Solution

Calcualte solubilities:

Solubility of Q = 1 g / 3 mL "hot acetone" = 0.3333 g/mL

Solubility of Q = 100 mg / 1mL of "cold acetone = 0.1000 g/mL

If we have;

m = 0.35 g initially

find min. solvent required for 100%

NOTE = the answer is "infinity" since this is a fractional process, in which the some initial amount will remain in the solution, for infinity since this is always fraciton based.

Let us assume for 99% recovery:

this implies

mass required = 0.35 g * 99/100 = 0.3465 g required

Change on solubility:

dS = 0.3333 -0.100 = 0.2333 g/mL

Then

Total mass / Soluibility = 0.3465 / 0.2333 = 1.4852 mL required for 99% recovery...

similar for 99.99%:

mass required = 0.35 g * 99.99/100 = 0.349965 g required

Change on solubility:

dS = 0.3333 -0.100 = 0.2333 g/mL

Then

Total mass / Soluibility = 0.349965/ 0.2333 = 1.50006 mL required for 99.99% recovery...

Then, assume the answer to be 1.5 mL

which is pretty good, since we are using 1.5 mL per gram, acetone is cheap so this will do great in a lab pratice


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