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Question
Differentiate the function of concentrated sulphuric acid as a drying agent & as a dehydrating agent. Is fused calcium chloride a dehydrating or a desiccating agent. Give reasons.
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Solution
Sulphuric acid (cone.) acts as drying agent when it removes water from other substances i.e. for drying gases.
Cone, sulphuric acid acts as dehydrating agent when it removes chemically combined water from compounds due to it strong affinity for water.
\[\ce{\underset{\text{ethanol}}{C2H5OH} + ->[Conc. H2SO4][dehydrating agent] \underset{\text{ethene}}{C2H4} +\underset{\text{water}}{H2O}}\]
Cone. H2SO4 has removed H20 from ethanol and changed it to ethene. Fused calcium chloride [CaCl2] is desiccating agent as it is drying the substance.
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