Saturated Solutions & Curves: Temperature Effect, Crystallisation / Recrystallisation

Understanding Crystallisation and Recrystallisation

Crystallisation is the process of forming solid crystals from a solution. Recrystallisation is used to purify substances by dissolving impurities and forming pure crystals.

Temperature's Effect on Solubility

• Increased Temperature: Generally increases solubility for most solids, allowing more solute to dissolve.
• Decreased Temperature: Can lead to crystallisation as the solution becomes supersaturated, causing excess solute to form crystals.

Crystallisation Process

1. Prepare a Saturated Solution: Dissolve the solute in a solvent at high temperature until no more dissolves.
2. Cool the Solution: Slowly reduce the temperature to allow crystals to form as solubility decreases.
3. Collect Crystals: Filter out the crystals from the remaining solution.
4. Dry the Crystals: Remove any remaining solvent to obtain pure crystals.

Recrystallisation Steps

1. Dissolve Impure Substance: Use a suitable solvent to dissolve the impure substance at high temperature.
2. Filter the Solution: Remove insoluble impurities by filtration.
3. Cool the Solution: Allow pure crystals to form as the solution cools.
4. Collect and Dry Crystals: Filter and dry the pure crystals.