Experiment 1 Solvent of crystallization
Objective:
To select a solvent appropriate for recrystallization of (a) trans-stilbene, (b) 9fluorenone or (3) benzoic acid
Each student will be assigned a compound (one of the above three compounds) to find a solvent suitable for its crystallization; Solvent choices n-hexane, toluene, acetone, ethanol and water
Pre-Lab [Obtain the following Substance Information for all chemicals used in your experiment]
Molecular formula (MF), Structure, molecular weight, melting point (for solutes) / boiling points (for solvents) and lab hazards (volatile, flammable, corrosive, irritant etc)
A) C14H12, crystal, 180.25 g/mol, 123 – 125oc, 305 -307oc, causes eye irritation, harmful if swallowed.
B) C13H8O, , 180.20g/mol, 80 – 83oC, 342oC, irritant,
C) C7H6O2, , 122.12g/mol, 121-125oC, 249oc, flammable, irritant
Method:
Criteria for a solvent to be suitable for use to recrystallize a solid:
The solid sample should (a) have a melting point higher than the boiling point of the solvent, (2) be insoluble in the solvent at room temperature,(3) soluble in the solvent at a higher temperature and (4) crystallize, from its hot clear solution in the solvent, upon cooling to room temperature
(a) Compare the physical constants to eliminate solvent choices
(b) Determine solubility of each solid substance in each of the five solvents at room temperature ; Identify solvents that are not suitable for recrystallization (Those in which the solute dissolves completely at room temperature)
(c) From among those solvents which may be suitable for recrystallization Determine solubility of each substance in hot solvents
(d) Determine ability of a hot solution to produce crystals of the solid on cooling
