Question

Differentiate a hygroscopic substance from a deliquescent substance...
atleast 2 points for each

Answer 1

HYGROSCOPIC MIXTURE:This is when substances absorb water from air, but not enough to form solutions. Examples of such substances include CaO, NaNO3, NaCl, Sucrose and CuO. Also, certain liquid substances absorb water from the air to get diluted - these are also regarded as being hygroscopic. Example, conc. H2SO4 and conc. HCl. lf a hydroscopic substance absorbs so much moisture that an aqueous solution is formed, the substance becomes deliquescent. DELIQUESENCE =This is when certain solid substances, when exposed to air absorb water, enough to form solutions. Example, solid NaOH, CaCl2, CaCl2. 6H2O, P4O10 (forms HPO3), FeCl3, KOH, MgCl2.

Note: substances which absorb water from air can be used as drying agents for gases. Example, CaCl2 and P4O10 can be used to dry gases, but not ammonia. Conc. H2SO4 is used to dry HCl. CaO or silica gel is suitable for drying ammonia gas, this is because CaCl2 , P4O10 and H2SO4 will react with the ammonia.

Answer 2

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The water soluble substance which absorb moisture from the air and then dissolve on the absorbed moisture to change into liquid taste are called deliquescent substances whereas the substances which absorb moisture from air but do not change their state are called hygroscopic substances.