Question

How many Faradays of charge is required to convert 1 mole Cr2O7 to Cr3+

Answer 1

To convert
+7 oxidation state of Cr to +3
=(7-3) Faradays
=4F

Answer 2

Answer: 6 Faraday

Explanation:

$Cr_2O_7^{2-}+14H^++6e^-\rightarrow 2Cr^{3+}+7H_2O$

Thus 6 moles of electrons are involved in conversion of 1 mole of  $Cr_2O_7^{2-}$ to $Cr^{3+}$.

1 electron carry charge=$1.6\times 10^{-19}C$

1 mole of electrons contain=$6.023\times 10^{23}$ electrons

Thus  

1 mole of electrons carry charge=$\frac{1.6\times 10^{-19}}{1}\times 6.023\times 10^{23}=96500C=1 Faraday$

6 mole of electrons carry charge=$6\times 1=6Faraday$