Page 112 - Chemistry ICSE Class X

98 ICSE Chemistry – 10

— Hygroscopic substances. The substances which absorb moisture (water vapour) from the atmosphere without dissolving
in it are called hygroscopic substances.
Some common hygroscopic substances are: Anhydrous calcium chloride, conc. sulphuric acid, silica gel, phosphorus
pentoxide.
— Deliquescent substances. Certain anhydrous or partially hydrated salts which can absorb moisture from the air, become
moist and finally dissolve in the absorbed water forming a saturated solution are called deliquescent substances.
Caustic soda (NaOH), magnesium chloride (MgCl ), zinc chloride (ZnCl ), calcium chloride (CaCl ) are some typical
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deliquescent substances.
— Drying agent. The substances which can remove moisture from other substances are called drying agents (or desiccating
agents). Phosphorus pentoxide (P O ), quicklime (CaO), silica gel are drying agents.
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— Dehydrating agents. The substances which can remove water present in the structure of any compound/salt are called
dehydrating agents. Conc. sulphuric acid is a strong dehydrating agent.