Physical Properties
1. They are colourless, poisionous and corrosive gas having pungent ordour. They are
nasal throat and lungs irritant.
2. They are higly soulble in water. They dissolve to form sulphorus acid and they are heavier than air.
3. They liquidify at -10 C to form colourless liquid and solidifies at 76 C.
Chemical properties
1. Acidic nature :
Sulphur dioxide gas is an acid anhydride of Sulphurous gas, it dissovles to form Sulphurous gas which is a weak diprotic acid.
H 2SO3 --------------> H3 O- + HSO3 -
HSO 3 --------------> H 3-O + SO 3--
When such type of diprotic acid reactes with base it undergoes nutralization reaction in two ways forming neutral and acidic salt.
H2 SO 3 + NaOH --------------> H 2O + Na2 SO3 (Acidic salt)
H2 SO 3 + NaOH --------------> H2 O + NaSO 3 (Neutral salt)
2. Sulphur dioxide as reducing agent :
It is strong reducing agent.
a. It reduces halogens to haloacids.
Cl + H2 O --------------> HCl + [O]
[O] + SO 2 + H 2O --------------> H2 SO 4
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Cl+ H 2O + SO2 --------------> HCL + H 2SO 4
b. It reduces Ferric salt to ferrous salt.
SO2 + H 2O --------------> H 2SO4 + [H]
[H] + Fe2 (SO4)3 --------------> FeSO4 + H2 SO 4
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