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An aqueous solution containing one mole ...

An aqueous solution containing one mole of `HgI_2` and two moles of NaI is orange in colour. On addition of excess NaI the solution becomes colourless. The orange colour reappears on subsequent addition of NaOCl. Explain with equation.

Text Solution

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A solution containing one mole of `Hgl_(2)` and two mole of Nal is orange in colour due to the partial solubility of `Hgl_(2)`. On addition of excess of Nal, the colourless complex `Na_(2)Hgl_(4)` is formed.
`underset(("Excess"))(2Nal)+Hgl_(2)to underset("Nessler's reagent")(Na_(2)Hgl_(4))`
the `Na_(2)Hgl_(4)` on addition of `NaOCl`, oxidises as
`3Na_(2)Hgl_(4)+2NaOCl+2H_(2)O to 3Hgl_(2)+2NaCl+4NaOH+2Nal_(3)`. thus, colour of partially soluble `Hgl_(2)` is restored.
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