After separation, the organic layer still contains traces of water, which make it look cloudy. It is dried by adding an anhydrous salt (a drying agent), which absorbs water to form a hydrated salt. Common drying agents are anhydrous magnesium sulfate, MgSO4, and anhydrous calcium chloride, CaCl2.Method
1. Run the organic layer into a dry conical flask.
2. Add a spatula of drying agent, stopper the flask and swirl.
3. If the solid clumps together, water is still present, so add more until some of the solid stays free-flowing when swirled.
4. Leave the stoppered flask for several minutes. The liquid should turn from cloudy to clear.
5. Separate the dried liquid from the solid by decanting it or by filtering it.The flask is stoppered so that the organic liquid does not evaporate and water vapour from the air is not absorbed. The drying agent must not react with the product: for example, anhydrous calcium chloride is not used for alcohols because it forms compounds with them. Magnesium sulfate works quickly and absorbs a lot of water, so it is a good general drying agent.Example: a student adds anhydrous magnesium sulfate to a cloudy sample of cyclohexene. The first portion clumps, so more is added until the powder moves freely and the liquid is clear. The dry cyclohexene is then decanted, ready for redistillation.
1. Run the organic layer into a dry conical flask.
2. Add a spatula of drying agent, stopper the flask and swirl.
3. If the solid clumps together, water is still present, so add more until some of the solid stays free-flowing when swirled.
4. Leave the stoppered flask for several minutes. The liquid should turn from cloudy to clear.
5. Separate the dried liquid from the solid by decanting it or by filtering it.The flask is stoppered so that the organic liquid does not evaporate and water vapour from the air is not absorbed. The drying agent must not react with the product: for example, anhydrous calcium chloride is not used for alcohols because it forms compounds with them. Magnesium sulfate works quickly and absorbs a lot of water, so it is a good general drying agent.Example: a student adds anhydrous magnesium sulfate to a cloudy sample of cyclohexene. The first portion clumps, so more is added until the powder moves freely and the liquid is clear. The dry cyclohexene is then decanted, ready for redistillation.