Question

the solubility of a compound is 59 g / 100 ml in boiling methanol and 30 g / 100 ml in cold methanol. how much mass would you recover if you take 7.2g of compound and dissolve it in 100 ml of boiling methanol and then cool it down to 2°c and filter it.

Explanation:

Step1: Determine the solubility at cold temperature

The solubility of the compound in cold methanol is 30 g/100 mL. This means that when 100 mL of the solution is cooled, 30 g of the compound will remain dissolved.

Step2: Calculate the mass of the compound that precipitates

We started with 7.2 g of the compound in 100 mL of boiling - methanol. After cooling to 2°C, the amount of compound remaining in solution is 30 g (since the solubility at cold temperature is 30 g/100 mL).
The mass of the compound recovered (precipitated) is the initial mass minus the mass remaining in solution.
The initial mass of the compound is 7.2 g and the mass remaining in solution is 30 g (for 100 mL at cold temperature). But since we started with 7.2 g which is less than the solubility at cold temperature (30 g/100 mL), no compound will precipitate out. The mass recovered is 0 g.

Answer:

0 g