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CHEM 315 GMU Find The Amount of Methanol Needed to Recrystallize Chemistry Ques

  1. If the solubility of cholesterol in methanol were 1 g/96 mL at 20ºC and 1 g/4.1 mL at 80ºC, what is the absolute minimum amount of methanol needed to recrystallize 5.13 g cholesterol? Report the number of mL to the nearest whole number.
  2. In recrystallization experiments, not all of the starting material is ever recovered, even if the initial material was 100% pure. To determine the % recovery, the ratio of final to starting masses of material is taken and converted into a percentage. In an experiment, 5.7 g of impure fluorene is recrystallized in 10 ml ethanol. After filtration and drying, 5.5 g of fluorene crystals are found on the filter paper. What is the percent recovery? List the percent to the nearest whole number and do not include the % sign.
  3. If the solubility of cholesterol in methanol were 1 g/99 mL at 20ºC and 1 g/4.2 mL at 80ºC, what is the maximum mass of cholesterol that could be recrystallized from 5.44 g cholesterol? Report the number of grams to two decimal places.
  4. Calculate the maximum % recovery possible if the solubility at room temperature is 1g/461 mL and at the boiling temperature of the solvent is 1g/14 mL. Report your answer as a percentage to the nearest whole number, without the percent sign.
  5. It is important to always minimize the amount of solvent used, allowing for evaporation. If we add a relatively large excess, we expect our recrystallization to produce lower percent recoveries. A common mistake is to misplace the decimal, resulting in addition of 11x the solvent instead of the recommended 1.1x. If a substance dissolves in a solvent at 1g/459 mL at room temperature and at 1g/13 mL at the solvent’s boiling point, what would be the maximum expected amount recovered if using 11x the minimum amount of solvent in recrystallizing 10 g of the substance? Report your answer in grams to one decimal place.


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