Question

In an electrolytic cell, one liter of 1M aqueous solution of MnO${{}_4}^{-}$ is reduced to MnO${{}_4}^{-2}$ at a cathode. How many faradays would be required so that the solution becomes 0.899M $Mn{O}_4^{-}$:

• A. 10 Faradays
• B. 0.1 Faradays
• C. 1.0 x 10${}^{-4}$ Faraday
• D. 1x10${}^{-4}$ Faraday

Answer 1

Answer: (B)

0.1 Faradays

$Mn{O}_4^{-}\to Mn{O}_4^{-2}$
$+7$ $+6$
[M] changes from 1 M to 0.8999
$\therefore$ change in moles of $Mn{O}_4^{-}$=1-0.899=0.101$and$no. of factor=1\therefore no. of moles of electron require=0.101\times 1=0.101no. of faraday of charge = no. of moles of e^- required=0.1 F$