Drying

After removing inorganic impurities by washing, the remaining contaminant is water.

 

Removal of water consists of two steps: predrying and drying.

1. Predrying

Washing a wet organic solution with saturated aqueous NaCl solution (or "brine") removes the bulk of water dissolved in the organic layer.

 

Saturated NaCl solution is a very polar medium, and water, which is also a polar compound, will move to the polar layer, rather than staying in the nonpolar organic medium.

 

2. Drying

To remove the trace of water remaining after predrying, a drying agent is used.

 

A drying agent is an anhydrous inorganic salt, such as calcium chloride (CaCl₂), magnesium sulfate (MgSO₄), and sodium sulfate (Na₂SO₄). These solids are insoluble in organic solvent, and readily absorb water to form hydrates.

 

 

You add sufficient solid drying agent to the organic solution, stopper the flask, then set the mixture aside for several minutes. You can remove the hydrated drying agent simply by gravity filtration.