Generally, organic substances, that are liquid or solid, are insoluble in water because they are not as polar as water. Due to polarity, organic compounds can dissolve a certain amount of water, which varies from solvent to solvent. The more polar a substance is, the more easily it absorbs water. Every time an organic compound is in contact with water, a small amount of substance will be dissolved in it and also a quantity of water will be found in that organic compound. It is considered that water is hard to be removed from the compounds because they are forming strong bonds with water molecules (eg alcohols) or the compound is volatile.
For a solid organic compound, water can be easily removed by simple exposure to atmospheric pressure or at a reduced pressure. Sometimes, it can be used a low temperature oven to facilitate drying. With most liquids, vapor pressure is high and this thing prevents the use of any of the previous methods to remove water from their composition.
When a liquid organic compound has been exposed to water, a drying agent is frequently used. This is usually an inorganic and insoluble salt which fast absorbs water and it's becoming hydrated. Most of drying agents used in the laboratory of organic chemistry are: calcium chloride (CaCl2), sodium sulfate (Na2SO4), calcium sulfate (CaSO4) and magnesium sulphate (MgSO4), found in an anhydrous state.
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