Chemistry PREPARATION AND PROPERTIES OF SODIUM THIOSULPHATE

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PREPARATION AND PROPERTIES OF SODIUM THIOSULPHATE

Preparation :

(i) See fig.1.

(ii) `undersettext(Salt Coke)(Na_2SO_4) + undersettext(Coke)(4C) oversettext(roasting)-> Na_2S + 4CO`

` Na_2S overset[SO_2 text(passed into it)] -> Na_2S_3O_3 [3SO_2 + Na_2S -> 2Na_2S_2O_3 + S]`

(iii) `2Na_2S + Na_2CO_3 + 4SO_2 -> 3Na_2S_2O_3 + CO_2`

(iv) `6NaOH + 4S -> Na_2S_2O_3 + 2Na_2S + 3H_2O`

`3Ca(OH)_2 + 12 S -> CaS_2O_3 + 2CaS_2O_3 + 3H_2O`

(v) `Na_2SO_3 + Na_2S + I_2 -> Na_2S_2O_3 + 2NaI`

(vi) `2Na_2S + 2O_2 + H_2O -> Na_2S_2O_3 + 2NaOH` [`Na_2S` is readily oxidised in air giving rise to `Na_2S_2O_3`]

Properties :

(i) `4Na_2S_2O_ 3 -> Na_2S_5 + 3Na_2SO_4`

(ii) `Na_2S_2O_3 + 2H^(+) -> H_2S_2O_3 ->H_2O + SO_2 + S downarrow` (White turbidity)

Reaction : (i) `Na_2S_2O_3 + I_2 -> S_4O_6^(2-) + 2I^(-)`

`Na_2S_2O_3 + Cl_2 -` water `-> SO_4^(2-) + S + 2HCl`

`Na_2S_2O_3 + Br_2 -` water `-> SO_4^(2-) + S + 2HBr`

`Na_2S_2O_3 + 4OI^(-) + 2OH^(-) -> 2SO_4^(2-) +4I^(-) + H_2O`

`Na_2S_2O_3 + undersettext(excess)(4 Cl_2) +5 H_2O -> Na_2SO_4 +8HCl + H_2SO_4`