Hydrated Salts - Definition and Types

 Certain Salts contain definite amount of some H2O molecules loosely attached to their own molecules. These are known as Hydrated salts and are of crystalline nature. The molecules of H2O present in water are known as 'water of crystallisation' . 

TYPES OF HYDRATED SALTS 

Efflorescence salts 

Certain hydrated salts when exposed to atmosphere at ordinary temperature , lose their water of crystallisation molecules either partially or completely and become anhydrous. These are known as efflorescent salts and this property is known as efflorescence. It increases under dry weather conditions and in summer when ordinary temperature is quite high. 

examples- Washing soda , epsom salt and blue vitriol 

Deliquescence salts 

Certain substances have the property to absorb moisture when exposed to atmosphere at ordinary temperature. They initially become wet , lose their crystalline forms and ultimately dissolve in absorbed water to form a solution. Such substances are known as deliquescent substances and this property is called deliquescence.

examples-Sodium hydroxide , potassium hydroxide, ferric chloride, hydrated calcium chloride etc .

Hygroscopy 

Certain substances also absorb moisture from atmosphere at ordinary temperature but do not dissolve in it. These are called hygroscopic substances and this property is known as hygroscopy. 

NOTE -  Hygroscopic substances are mostly used as drying agents particularly for gases. 

examples- Anhydrous calcium chloride , concentrated H2SO4 , phosphorus pentoxide , quick  lime , silica gel etc.