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  4. The amount of current in Faraday is required for the reduction of 1 mol of Cr2O72- ions to Cr3+ is,

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Q. The amount of current in Faraday is required for the reduction of 1 mol of $Cr_2O_7^{2-}$ ions to $Cr^{3+}$ is,

KCETKCET 2016Electrochemistry

Solution:

$\underset{(+C)}{Cr_2}O^{2-}_{7} \longrightarrow \underset{(+3)}{Cr ^{3+}}:$ Oxidation number of $Cr$

It shows change in oxidation number, i.e. change of 3 moles of electrons per mole of Cr-atom.

$\because Cr _{2} O _{7}^{2-}$ has 2 moles of Cr-atoms. Hence, total 6 moles of electrons, i.e. $6 F$ of charge (current) is required for reduction of 1 mole of $Cr _{2} O _{7}^{2-}$ ions.