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A drying agent is a chemical used to remove water from an organic compound that is in solution. In making or isolating chemical compounds they often become contaminated with water. If you want to dry a compound that is in solution, a saturated (highly concentrated) solution of sodium chloride can be used to remove the extra water. Water will move from an area of higher concentration (the compound solution) to an area of lower concentration (the saturated salt solution). You will get 2 layers: the salt solution layer and the layer of "dried " organic compound solution. The pure compound can then be separated from the salt solution layer. Drying agents can also be solid like Calclium chloride, Potassium chloride, or Magnesium sulfate. These are all types of salts (ionic compounds where metals are bonded to nonmetals.) These drying agents are added to the solution of a compound that needs to be dried. The agents will easily pick up any extra water from the compound solution and become hydrated. The hydrated salts form clumps which can be filtered out or left behind during decanting resulting in a "dry" compound. There are good pictures of this at the link below.
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.
Drying or dessicating agents remove moisture from other substances superficially.Almost all hygroscopic substances are drying agents.Ex-Conc.sulphuric acid,phosphorous pentoxide,quicklime & silica gel.Removal of water is physical change.
Dehydrating Agents-remove chemically combined elements in ratio 2:1.Removal of moisture is Physical change.
A drying agent is meant to remove water from a sample. In high school chemistry drying agents most commonly used could be alcohol or acetone.
Frequently we want to "dry" samples before getting a final mass to calculate how much product we produced.
See your textbook for more information.
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