posted by John on .
The solubility of a compound is 59g per 100mL in boiling methanol and 30g per 100mL in cold methanol, whereas its solubility in water is 7.2g per 100mL at 95C and 0.22g per 100mL at 2C. Which solvent would be better for recrystallization of the compound? Explain
I am not quite sure how to start it out.
In methanol, almost half still is dissolved in cold methanol.
In water, only three percent is still dissolved.
Besides, who wants to stir boiling methanol?
If percent recovery is not an issue, either solvent will work ok. However, note that using methanol loses half the product. From a personal standpoint, I would choose water. It is less soluble BUT the loss is very low.
I sort of see it now. I was wondering what is the formula used to calculate the percent recovery?
Just like any percent.
In this case, you get 29 g (59-30) back in the cold methanol and you started with 59g; therefore,
%rec =(29/59)*100 = 49% recovered. 51% is lost. (We could have chosen any number to start that we wanted and used proportions to determine how much was soluble at the higher T and how much was soluble at the lower T, but why makes things hard? I just chose 59 g so we KNOW that will dissolve and will leave 29 g at the end. )
If biphenyl dissolves in both cold and hot methanol, would this be a good recrystallization solvent for biphenyl? Explain please!!!