Help with Recrystallization Lab Questions

Sep 20th, 2015
Steve1995
Category:
Chemistry
Price: $10 USD

Question description

2) You dissolve an amount of solid Q in 195.0 mL solvent, forming an unsaturated solution. The solubility of Q at 0°C is 0.87 g/100 mL. The amount of solid remaining in solution at 0°C is 13.0% of the original amount of solid dissolved. What is the original amount of solid that was dissolved (report to 1 decimal place)? 

3) What can one do to obtain a second crop of crystals after initial crystals have been collected? What is the drawback of this method?

 4) If you are using a trial-and-error method to pick a solvent for recrystallization, why would it be advisable to try low-boiling solvents first, especially if you have a limited sample of solid that you wish to recrystallize?

5) You are given a unknown white solid to recrystallize in lab. The white solid could be Compound A (melting point 110-112°C), Compound B (melting point 66-68°C) or Compound C (melting point 92-93°C). Compound A, B and C are significantly soluble in ethyl acetate (bp: 78°C), even at room temperature and not very soluble in water (bp: 100°C) or toluene (bp: 111°C) (difference in solubility of solid in water and toluene is not significant) . Ethyl acetate is miscible with toluene but not with water.

a) Why would one choose toluene over water to pair with ethyl acetate to use as a solvent pair?
b) If you decide to use toluene and ethyl acetate as the solvent pair for the unknown white solid, describe which solvent you would heat up and dissolve the solid in initially and which solvent you would add second and at what point would you stop adding the second solvent.
c) If you could use ethyl acetate as the single recrystallization solvent for the solid, which compound might have a problem of oiling out and why?

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