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Explain properties of sulphur dioxide. State its uses. |
Answer» Solution :(i) Physical properties : Sulphur dioxide is a COLOURLESS gas with pungent smell and is highly soluble in water. It boils at 263 K and liquefies at room temperature under a pressure of 2 atm. The shape of `SO_(2)`is angular. It is resonance hybrid of two canonical forms.  (ii) Chemical properties : S02 when passed through water forms a solution of sulphurous acid. `SO_(2)(g) + H_(2)O(l) Mimplies H_(2)SO_(3)(aq)` It readily reacts with NaOH solution, forming sodium sulphite, which reacts with more sulphur dioxide to form sodium hydrogen sulphite. `2NaOH + SO_(2) to Na_(2)SO_(3) + H_(2)O` `Na_(2)SO_(3) + H_(2)O + SO_(2) to 2NaHSO_(3)` The S02 behaves very similar to `CO_(2)`in its reaction with water and alkalies. Sulphur dioxide reacts with chlorine in the presence of charcoal (Catalyst) to give sulphuryl chloride `SO_2Cl_2`. `SO_(2)(g) + Cl_(2)(g) to SO_(2)Cl_(2)(g)` In presence of vanadium (V) oxide, it oxidizes to `SO_3`. `2SO_(2)(g) + O_(2)(g) overset(V_(2)O_(5))to 2SO_(3)(g)` The moist sulphur dioxide act as reducing agent. For example, it CONVERTS Fe(III) ions to Fe(II) and decolourises potassium permanganate solution. The reaction with potassium permanganate is used for TEST of `SO_(2)(g)` `2Fe^(3+) + SO_(2) + 2H_(2)O to 2Fe^(2+) + SO_(4)^(2-) + 4H^(+)` `5SO_(2) + 2MnO_(4)^(-) + 2H_(2)O to 5SO_(5)^(2-) + 4H^(+) + 2Mn^(2+)` Uses of `SO_(2)`: i)In refining of petroleum and sugar. (ii)In bleaching of wool and silk. (iii)As an anti colour, disinfectant and preservative. Industrial CHEMICALS such as `H_2SO_4, NaHSO_3` and `Ca(HSO_3)_2` are prepared from `SO_2`. Liquid `SO_2` is used as SOLVENT to dissolve a number of inorganic and organic chemicals. |
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