Drying

After solvent extraction, the organic layer still contains small amounts of water. Traces of water make an organic liquid look cloudy. Water is removed with a drying agent before the final distillation.A drying agent is an anhydrous salt that absorbs water to form a hydrate. Common drying agents are:• anhydrous magnesium sulfate• anhydrous sodium sulfate• anhydrous calcium chlorideFor example:MgSO₄(s) + 7H₂O(l) → MgSO₄.7H₂O(s)Method• Run the organic layer into a dry conical flask.• Add a small spatula of the drying agent, stopper the flask and swirl.• At first the solid clumps together as it takes up water. Keep adding small amounts until the liquid is clear and some of the solid no longer clumps together but moves freely when swirled.• Leave for a few minutes, then separate the liquid from the solid by decanting or filtering.The drying agent must not react with the product or dissolve in it. Anhydrous calcium chloride is used to dry halogenoalkanes, but it is not used to dry an alcohol, because it also absorbs alcohols. This can be useful: it removes traces of unreacted alcohol from a halogenoalkane product at the same time as the water.The dried liquid is then purified by distillation, collecting the fraction that boils close to the boiling temperature of the product.