The solubility of compound in various solvents is given below: Which of the abov
ID: 1067897 • Letter: T
Question
The solubility of compound in various solvents is given below: Which of the above solvents would be the best choice to purify Compound X by recrystallization? Explain your choice. How many mL of your chosen solvent would beta needed to dissolve 25 g of compound X? A student was performing a recrystallization of compound x with the chosen solvent. The solvent was heated to 30 degree C and added to compound X, Once the compound was dissolved, the student allowed it to cool to room temperature and evaporated the solvent. A solid was collected and further test were done. Identify the mistake(s) the student made in the recrystallization of compound X and state how the mistake(s) would affect the outcome of their results.Explanation / Answer
Crystalization is a process of separating from solute from the solvent by taking advantage of solubility of solute in the solvent during cooling. Hence crystalization is based on the difference in solubility of solute in the solent between those temperatures. Higher the solubility difference, higher the amount of crystals formed. The solubility difference for all the given solvents
water : (0.89-0.06)/100ml =0.83g/100ml, Ethanol = (3.5-0.88)/100ml =2.62g /100ml, dichloroethane = (21.3-0.67)g/100 = 20.63/100ml, diethyl ether = (22.4-15.4)/100ml= 7 gm/ml
So maxium separation can be achieved using dichloroethane. Less solvent is required for more removal of solute X. More over, its boiling point is less.
20.63 gm are separated from 100ml during crystalization.
25 gm are separared from 100*25/20.63=121.1827 ml
2. When the solvent was heated and added, the solubility was increased purposefully. So the student would have heated the solvent upto boiling point so as to dissolve maxium amount of solvent. Since the solubility at 30 deg.c is less than the solubility at the boiling point, less amount of solute is dissolved, lesse the separation since higher separation is possible if the solubility difference is more.