Question

 
Recrystallization Lab using water and the solvent pair is methanol water.

 1.You are given a known solid substance with its melting point which has  high solubility in hot water and low solubility in cold water.  You are assigned the
following task:

 i. determine if the substance is pure

ii. if impure, find a suitable method for its purification by using the given information about the substance

How you would proceed, clearly explain your rationale? 

Answer 1

1. mix known quantity of solid substance (with impurities), lets say x grams, in hot water.
2. Slowly cool the mixture, the pure substance would slowly crystallize out, leaving the impurities still dissolved.
3. The crystallized out solid is taken out, dried and its mass is measured. Lets say it weighs x' grams.
4. If x=x', then there are no impurities and the given substance was pure. Otherwise, the amount of impurities is x-x' grams.
5. Impurities are already separated in the above step.