Define the following and give an example: Efflorescent substances

Definition of efflorescent substances-The salts which lose water of crystallisation either completely or partially on exposure to air is called efflorescent substances and the phenomenon is called efflorescence. Washing soda and Glauber’s salt ( Na 2 SO 4 . 10 H 2 O ) are examples of efflorescent substance. It loses nine water molecules on exposure to air and the remaining one water molecule on heating.

Define the following and give an example: Deliquescent salts

Some salts on exposure to the atmosphere and absorb moisture from the atmosphere dissolve in it and change into a liquid, such salts are called deliquescent salts. Thus deliquescent salts are moisture absorbing salts that form a solution by simply absorbing the water vapours from the atmosphere. Example: Calcium chloride CaCl 2 and magnesium chloride MgCl 2 .

Define the following and give an example: Hygroscopic salts

Hygroscopic substances or compounds are those that absorb the water from the vapour or the liquid that is present in the environment. Its main application is desiccant. These substances do not undergo any change in physical state on the absorption of moisture from the atmospheric air. These are called Hygroscopic substances. Examples: Sodium chloride, calcium chloride, cobalt chloride, etc.