Question

The solubility of "Compound Y" in hot ethanol (78 °C) is 0.13 g/mL, and 0.03 g/mL in cold ethanol (0 °C). For this question, assume that the lowest temperature you can achieve in the teaching lab is 0 °C. Show your work. i) What is the minimum amount of hot ethanol required to recrystallize a 1.60 g sample of Compound Y (assuming the sample is less than 0.01% impure)? ii) Under ideal conditions what is the maximum amount (also provide percent recovery) of purified Compound Y that can be recovered in Part i. iii) What is the maximum amount (also provide the percent recovery) of purified Compound Y that can be recovered if 30 mL of ethanol w

Answer 1

i) 16 mL of ethanol

ii) maximum amount recoverable = 15.52 g; percentage recovery = 97%

iii) maximum amount recoverable = 15.1 g

percentage recovery = 94.4%

Step-by-step explanation:

Solubility = mass/volume

i) mass of ethanol recovered per mL of ethanol when cooled from 78 °C to 0 °C = 0.13 - 0.03 = 0.10 g

Therefore 1.60 g of Y will require a minimum of 1.60 x 1 mL/0.10 g = 16 mL of ethanol

ii) maximum amount of Y that can be recovered is given as :

mass of Y left in solution after recrystallization, x is obtained

0.03 g/mL = x g/16 mL

x = 0.48 g

maximum amount recoverable = 16 - 0.48 = 15.52 g

percentage recovery = (15.52/16) x 100 % = 97%

iii) if 30 mL of ethanol were used:

mass of Y left in solution after recrystallization, x is obtained;

0.03 g/mL = x g/30 mL

x = 0.03 x 30 = 0.9 g

maximum amount recoverable = 16 - 0.9 = 15.1 g

percentage recovery = (15.1/16) x 100% = 94.4%