Outline a procedure for separating a mixture of naphthalene (a neutral compound)

Question

Outline a procedure for separating a mixture of naphthalene (a neutral compound), toluic acid (an acidic compound), and p-bromoaniline (a basic compound). Assume that toluic acid and p-bromoaniline are completely insoluble in water. make sure that you indicate what is being separated or isolated in each step. The solubility of Lorazepam is 0.07 mg/mL and 2.87 mg/mL, in water and chloroform, respectively. Estimate the partition coefficient of lorazepam between chloroform and water. The solubility of benzoic acid at 25

Explanation / Answer

FOLLOW THIS 1. At 100 C 6.80 g benzoic acid needs 100 mL water to dissolve it,so 1.00 g benzoic acid needs 100/6.80 mL = 14.7 mL to dissolve it (NB. not part of the question but this means that 15 mL water at 100 C will be enough to dissolve all of the benzoic acid in Question 2 until it cools and then it will start to crystalise)) 2. At 25 C 100 mL water is able to dissolve 0.34 g benzoic acid, so 1 mL water is able to dissolve 0.34/100 g benzoic acid and 15 mL water is able to dissolve 15 x 0.34/100 = 0.051 g benzoic acid This means that when the acid has crystallised from the solution 0.051 g of the the 1.00 g will stay dissolved,so only 1.00 - 0.051 = 0.949 g will form as crystals. The % this is of the total amount of benzoic acid, ie the percent recovered is 100 x 0.949/1.00 = 94.9% Hope this helps you understand the principles of recystallisation as well as how to do the calculation.

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