1.

What is the potential for the cell `Cr|Cr^(3+)(0.1M)||Fe^(2+)(0.01M)|Fe` `E^(@)Cr^(3+)// Cr=-0.74V`, `E^(@)Fe^(2+)//Fe=-0.44V`A. `+0.2606V`B. `+0.5212V`C. `+0.1303V`D. `-0.2606V`.

Answer» Correct Answer - A
Anode half reaction : `CrrarrCu^(3+)+3e^(-)`
Cathode half reaction : `Fe^(2+)+ 2Cr^(3+)+6e^(-)`
or `Fe^(2)+6e^(-)rarr3Fe` cell reaction
`2Cr+3Fe^(2+)rarr2Cr^(2+)+3Fe,n=6`
Now `E_("cell")=E_("cell")^(@)-(0.05916)/(6)"log"([Cr^(3+)]^(2))/([Fe^(2+)]^(3))`
`=[-0.44-(-0.74)]-(0.05916)/(6)"log"((0.1)^(2))/((0.01)^(3))`
`=0.3-0.0394=+0.2606V`


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