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Author Question: The solubility of benzoic acid in water is 5.9 g/100 mL at 100C; 0.30 g/100 mL at 25C; and 0.17 ... (Read 55 times)

Collmarie

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on: Aug 23, 2018
The solubility of benzoic acid in water is 5.9 g/100 mL at 100C; 0.30 g/100 mL at 25C; and 0.17 g/100 mL at 0C. Can a mixture of approximately equal amounts of benzoic acid and salicylic acid be separated by recrystallization? Explain.

Question 2

A sample consists of, at most, 100 mg of impure salicylic acid. A student adds 1 mL of hot water and a boiling stick and heats the resulting mixture on the sand bath. Not all of the solid dissolves so the student continues to add hot water drop wise. After another 0.5 mL of water has been added, for a total of 1.5 mL, there is still some white solid remaining. Provide an explanation and advise the student as to how to proceed.


itsakadoozi

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Reply #1 on: Aug 23, 2018
Answer to Question 1

No. A one to one mixture of the two acids would be difficult to separate because their solubility profiles are too similar.

Answer to Question 2

According to the known solubility of salicylic acid, 1 ml of boiling water should dissolve 100 mg of salicylic acid. The remaining white solid is clearly an insoluble impurity. The hot solution should be filtered and the volume of the solution should be reduced. Then the solution should be cooled to crystallize the material.


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