1. A student wishes to recrystallize a sample of 4-bromobenzoic acid. How much b

Question

1. A student wishes to recrystallize a sample of 4-bromobenzoic acid. How much boiling water would it take to dissolve 5.0 g?

2. After adding the 5 g of 4-bromobenzoic acid to water at 100 degrees celsius and stirring, the student observes the formation of a solution (a homogenous mixture). What should the student do next (what is the next step of recrystallization)?

3. A 5.0 g sample of 4-bromobenzoic acid is dissolved in 300 mL of boiling water. How much 4-bromobenzoic acid will crystallize when it is cooled to 0 degrees celsius?

4. A student has a 10 g mixture that contains 9.5 g of 4- bromobenzoic acid and .5 g of benzocaine. If the student dissolves this mixture in 500mL of boiling water, and then cools it to 0 degrees celsius, how much benzocaine will crystalize?

Explanation / Answer

1. Assuming the standard data, solubility of 4-bromobenzoic acid in hot water is 5.63g/100mL

This means 5.63 grams dissolve in 100mL

1 gram will dissolve in 100/5.63mL

5 grams will dissolve in 100/5.63 x 5 = 88.81mL= hot water required.

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