Recrystallization is a technique used to purify impure solids by dissolving them in a hot solvent and slowly cooling the solution to allow the desired compound to crystallize out. There are different recrystallization methods like single-solvent or multi-solvent. For recrystallization to work, there must be a difference in solubility between the compound and impurities as temperature changes, so organic compounds are typically more soluble in hot solvents than cold solvents. The general procedure involves choosing a solvent, dissolving the impure compound in a minimum amount of hot solvent, filtering to remove impurities, and slowly cooling the solution to obtain purified crystals of the desired compound.

1. Recrystallization

2. Definition:
Impure solid compound is dissolved in a
solvent and then allowed to slowly crystallize out
as the solution cools.
There are also different recrystallization
techniques that can be used such as
A. Single-solvent recrystallization.
B. Multi-solvent recrystallization.

3. - In recrystallization, crude material is
formed in the minimum amount of hot
solvent.
- The solution needs to cool slowly until
one of the compounds within the solution
recrystallizes while the other stays in
liquid phase.

5. There must be a difference in
solubility to separate the desired
product from the impurities.
• Typically organic compounds are more
soluble in hot solvent than cold.
• The compound being recrystallized should be
dissolved in hot solvent but be insoluble in cold
solvent.
 Remember: “like dissolves like”
• Polar compounds dissolved in polar solvent, if
the polarities are too similar the compound will
dissolve but will not recrystallize.

6. Procedure for
Recrystallization
Choose a solvent
Dissolve the solute in a minimum
volume
Decolorize & Filter
All the system to cool slowly to
crystallize solute
Collect and wash crystals

7. Commonly used solvents
Solvent B.P Safety concerns
Water 100 None
Ethanol 24.5 Flammable, irritating to eyes and
respiratory system and skin
Acetone 56 Flammable, irritating to eyes , vapours
may cause drowsiness and dizziness
Ethyl Acetate 78 Flammable, irritating to eyes , vapours
may cause drowsiness and dizziness
Cyclohexane 81 Flammable, May damage lungs if
swallowed; Vapours may cause
drowsiness and dizziness

8. Thank you