1.

Sodium thiosulphate is prepared by :

Answer»

BOILING `Na_2SO_3` solution with elemental sulphur in alkaline medium
Boiling `Na_2SO_3` solution with elemental sulphur in acidic medium
Oxidation of poly sulphides , `Na_2S_3` with air
Reduction of bisulphite solution plus `SO_2` with zinc dust

Solution :(A)`Na_2SO_3 + S underset(OH^- or H_2O)overset("boiling")toNa_2S_2O_3`
(B)`S_2O_3^(2-)` formed in presence of acid precipitates sulphur and liberates `SO_2` gas according to the FOLLOWING reaction .
`S_2O_3^(2-)+H^(=)tounderset("DISPROPORTIONATION")(Sdarr`(white) + `SO_2) uarr H_2O`
(C )`2Na_2S_3 + 3O_2 underset("air")overset("heating")to2Na_2S_2O_3 + 2S`
(D)`2HSO_3^(-)+SO_2overset(Zn)to S_2O_4^(2-)+SO_3^(2-)+H_2O`


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