Due Recrystallisation ..?

Question

If characoal and sugar were impurities present in a sample of impue benzoic acid, explain how the recrystallisation from water would remove both ?

Answer 1

As benzoic acid crystallizes from water, the individual molecules arrange themselves into a repeating pattern.

It's sort of like putting together a jigsaw puzzle where all the pieces are identical. In this sort of jigsaw puzzle, it doesn't matter which piece goes where, since the pieces are all exactly alike. The charcoal and sugar would be puzzle pieces with different shapes. No matter where you try to put the charcoal or sugar pieces, they don't fit.

What probably happens with the benzoic acid, charcoal, sugar situation is that the impure benzoic acid is first dissolved in hot water. The charcoal is insoluble even in hot water, so the hot solution is filtered to remove the charcoal. Then the solution is chilled. The benzoic acid crystallizes, but the sugar molecules don't fit into the crystal lattice, so the sugar molecules remain in solution. The crystal-containing solution is filtered; pure crystals of benzoic acid are collected on the filter, and the sugar, still in solution, passes through the filter.

Answer 2

Charcoal is not soluble in water at any temperature. Sugar is soluble in water, but benzoic acid is only slightly soluble in hotter water. Benzoic acid is mostly insoluble in water because it is an organic molecule with an aromatic ring...therefore it is a not a huge fan of a polar, protic solvent such as water.

Heat it up, filter off the charcoal because both sugar and benzoic acid go into solution. Cool it back down, and the benzoic acid will crystallize out but the sugar will remain in solution. Filter off the benzoic acid...

Answer 3

well sugar is more soluble in water than benzoic acid so the impuritiy would be left behind as the water cools. the charcol is easily removed by hot filtration. reread about recrysalization