1) A student found that his unknown was soluble at the boiling point of hexane,

Question

1) A student found that his unknown was soluble at the boiling point of hexane, ethyl acetate and propanol (C3H7OH) but insoluble in water at all temperatures. What pair of solvents should he choose for the mixed solvent crystallization and how should he perform the crystallization? Explain how the crystallization process works with your chosen pair of solvents.

Options for Solvent Pairs

a) ethyl acetate, acetone

b) ethyl acetate, water

c) ethyl acetate, methanol

d) methanol, water

2) Assume that compound X melts at 160 degrees Celcius and compound Y melts at 130 degrees Celcius and a mixture containing 50% X and 50% Y melts at 100 degrees Celcius. If a student is given a mixture that contains 75% X and 25% Y, what will be the composition of the liquid phase after 25% of the solid has melted? (Hint- Construct a phase diagram and assume that the mixture contains 1,000,000 molecules.) What will be the composition of the solid and liquid after 60% of the sample has melted? When a liquid that contains 80% Y and 20% X is cooled, what will be compositions of the first and last crystals to form?

Explanation / Answer

a) ethyl acetate, acetone, c) ethyl acetate, methanol

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