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Question

Salicylic acid has the following solubility in water: 1.00g is soluble in 460ml at 0 degrees celsius and in 15ml of boiling water. A student performed recrystallization starting with 0.437g of crude salicylic acid dissolving it in 5.0ml of hot water. Calculate percent recovery of salicylic acid for the student.

Answer 1

Hello Uswah!

At 0°C, the solubility is 1.00g/460ml = 0.002174 g/ml

At 100°C (the temperature of boiling water) the solubility is 1.00g/15ml = 0.06667 g/ml

Now, to the recrystallization process, I will assume the hot water is at 100°C, because this is the only information we have. First we need to calculate the amount that can actually be dissolved in hot water:

0.06667 g/ml * 5ml = 0.33333 g dissolved

This process works by diminishing the temperature, so the solubility will decrease and the material will precipitate. The amount that can be dissolved in cold water ( I will assume it's 0°C) is:

0.002174 g/ml *5mL = 0.01087 g dissolved

The difference is the amount that precipitated:

0.33333 - 0.01087 = 0.32246g

The percentage recovered is the mass of precipitate divided by the initial mass:

%recovered = 0.32246g /0.437 g *100% = 73.79%