Pre Lab 
1. What is the ideal solvent for crystallization of a particular compound? What is the primary consideration in choosing a solvent for crystallizing a compound? volatile in order to be easily removed from the purified crystals.
In selecting a solvent consider that like likes like. Polar compounds dissolve polar compounds and non-polar compounds dissolve non-polar compounds.
Solvent will dissolve a large amount of the impure compound at temperatures near the boiling point of the solvent the compound would be completely insoluble in that solvent at room temperature or at zero oC
2. Impure benzoic acid was dissolved in hot water. The container of solution was placed in an ice-water bath instead of being allowed cooling slowly. What will be the result of cooling the solution in this manner? impurities are trapped inside the crystals being formed, thus, the crystals isolated are impure; Fast crystallization has smaller crystals with larger surface areas.
3. Outline the successive steps in the crystallization of an organic solid from a solvent and state the purpose of each operation.
1] dissolve solid product in minimum volume of hot solvent .. Purpose ... to get into solution
2] cool solution in a mixture of ice, water and salt. Purpose .. to enable pure product to crystallise, solubility decreases with temp, so cold. Impurities are present in small quantities, so do not saturate and are left in solution.
2a] if it all sets solid, you haven't used enough solvent, so add a little more and warm until everything dissolves. Purpose: you need solid and supernatent liquid to effectively filter and remove impurities.
3] Filter preferably by Buchner filtration. Purpose to remove surplus solvent
4] Wash filtrate with a little cold solvent. Purpose .. solid will be wet with solvent containing impurites .. need to wash this away .. but not so much that you lose a lot of your yield by it redissolving in solvent
5] let suction continue for a while. Purpose to remove bulk of
In selecting a solvent consider that like likes like. Polar compounds dissolve polar compounds and non-polar compounds dissolve non-polar compounds.
Solvent will dissolve a large amount of the impure compound at temperatures near the boiling point of the solvent the compound would be completely insoluble in that solvent at room temperature or at zero oC
2. Impure benzoic acid was dissolved in hot water. The container of solution was placed in an ice-water bath instead of being allowed cooling slowly. What will be the result of cooling the solution in this manner? impurities are trapped inside the crystals being formed, thus, the crystals isolated are impure; Fast crystallization has smaller crystals with larger surface areas.
3. Outline the successive steps in the crystallization of an organic solid from a solvent and state the purpose of each operation.
1] dissolve solid product in minimum volume of hot solvent .. Purpose ... to get into solution
2] cool solution in a mixture of ice, water and salt. Purpose .. to enable pure product to crystallise, solubility decreases with temp, so cold. Impurities are present in small quantities, so do not saturate and are left in solution.
2a] if it all sets solid, you haven't used enough solvent, so add a little more and warm until everything dissolves. Purpose: you need solid and supernatent liquid to effectively filter and remove impurities.
3] Filter preferably by Buchner filtration. Purpose to remove surplus solvent
4] Wash filtrate with a little cold solvent. Purpose .. solid will be wet with solvent containing impurites .. need to wash this away .. but not so much that you lose a lot of your yield by it redissolving in solvent
5] let suction continue for a while. Purpose to remove bulk of