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Deliquescence, Efflorescence and Hygroscopic Substances with Examples

When certain compounds are exposed to air, they either lose their water of crystallization or absorb moisture from their surroundings. The terms efflorescent, deliquescent, and hygroscopic describe such compounds.

Get the following substances: sodium hydroxide pellets, washing soda crystals (from an airtight container), quicklime, and concentrated tetraoxosulphate(VI) acid. Place small amounts of each substance on a watch glass and note their appearances carefully. Leave the substances in the open air for some time. Then, note any changes in their appearances.

Deliquescence and Examples

When exposed to the atmosphere, some compounds absorb a large amount of water, so they eventually turn into solutions. This phenomenon is known as deliquescence, and the substance is said to be deliquescent.

These substances include sodium hydroxide, iron (III) chloride, potassium hydroxide, calcium chloride, magnesium chloride, and phosphorus (V) oxide.

Read: Balancing chemical equations with examples

Efflorescence and Examples

Some crystalline salts will lose part or all of their water of crystallization when exposed to the atmosphere to form a lower dehydrate or anhydrous salt. This is known as efflorescence, and the salt is said to be efflorescent.

An example is the washing soda molecule which loses nine out of its ten molecules of water of crystallization when exposed to the atmosphere.

Na2CO3.10H2O -> Na2CO3.H20 (s) + 9H20 (g)

Hygroscopy

Hygroscopic substances also absorb moisture on exposure to the atmosphere. If they are solids, they will not form solutions but merely become sticky or moist. A hygroscopic liquid like concentrated tetraoxosulphate(VI) acid will absorb water from the air, usually diluting itself up to about three times its original volume. Hygroscopic substances are commonly employed as drying agents in the laboratory.

Other hygroscopic substances are sodium trioxonitrate(V), copper(II) oxide, and quicklime.

Bolarinwa Olajire

A tutor with a demonstrated history of working in the education industry. Skilled in analytical skills. Strong education professional with a M. SC focused in condensed matter. You can follow me on Twitter by clicking on the icon below to ask questions.
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