Explain the following observation: (1) Glycerol `[HOCH_(2) CH(OH)CH_(2)OH]` is a highly viscous liquid. (2) when 30 mL of water is added to 30 mL of ethanol, volume of the mixture becomes less than 60 mL.

Explanation

(1) glycerol molecule contains three -OH groups hence glycerol molecules remain extensively associated through intermolecular H-bonding. This accounts for high viscosity of glycerol
(2) The intermolecular H-bonding formed between ethanol and water is stronger than that formed in enthanol itself. when water is added to ethanol, the stronger intermolecular H-bonding between ethanol and water leads to contraction of volume. so, when 30 mL. of water is added to 30mL of ethanol, volume of the mixtrue becomes less than 60 mL.