Recrystallization

[Audio] Recrystallization 1. 1 Recrystallization.

[Audio] Recrystallization Recrystallization is a procedure for purifying an impure solid compound in a solvent. It is based on the principle that the solubility of most solids increases with increased temperature. If a saturated hot solution is allowed to cool, the solute is no longer soluble in the solvent and forms crystals of pure compound. Impurities are excluded from the growing crystals and the pure solid crystals can be separated from the dissolved impurities by filtration. Recrystallization works best when 1.the quantity of impurities is small 2.the solubility curve of the desired solute rises rapidly with temperature Purification Impure solid Pure solid.

[Audio] Recrystallization Purification Impure solid Pure solid.

[Audio] Principle Solvent =Room temp. Solid + Impurities Solid (Insoluble).

[Audio] Boiling Solid Solid (Insoluble) (Soluble).

[Audio] Representative Example The solubility of acetanilide in hot and in cold water is given in the table below. What is the maximum percent recovery if 5.0 g of acetanilide is recrystallized from 100 mL of water?.

[Audio] Answer: If 5 g of acetanilide is dissolved in 100 mL of water, it will all go into solution. When the solution cools, 0.53 g of this 5 g will not come out of solution; it will remain dissolved in the cold solvent. The amount of acetanilide that will come out of solution is (5 - 0.53) or 4.47 g. The maximum percent recovery is then 4.47/5 = 0.89 or 89%..

[Audio] 7 Steps to Recrystallization 1. Find "Best" solvent 2. Dissolve bulk sample in solvent 3. Decolorize (if necessary) 4. Remove insoluble impurities (if necessary) 5. Cool solute/solvent mixture 6. Collect crystals 7. Dry & analyze crystals.

[Audio] 1-Find "Best" solvent Characters of solvent for crystallization 1- Solubilize solid near or at its boiling point. 2- Solubilize impurities on cold. 3- Must be easily removed from purified solid crystals (low boiling point)..

[Audio] 4- Does not react chemically with purified solid. 5- Should yield well-formed crystals from purified solid. 6- Solvent b.p. should generally be lower than solid m.p. to avoid Oiling Out..

[Audio] Most commonly used solvents Water is the best solvent Ethanol, Methanol, Propanol Like dissolves Like.