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From the following data at 25^(@)C Cr^...

From the following data at `25^(@)C`
`Cr^(3+)(aq.)+3e^(-)rarr Cr^(2+)(aq.)`,
`E^(@)= -0.424V`
`Cr^(2+)(aq.)+2e^(-) rarr Cr(s), " "E^(@)= -0.900V`
Find `E^(@)` at `25^(@)C` for the reaction :
`Cr^(3+)+3e^(-) rarr Cr(s)`

A

`-0.741 V`

B

`-1.324` V

C

`-0.476` V

D

`+0.741 V`

Text Solution

Verified by Experts

The correct Answer is:
A
`Cr^(3+)(aq)+e^(-) rarr Cr^(2+)(aq)`,
`DeltaG^(@)= -1xxF xx - 0.424=0.424F` ....(i)
`Cr^(2+)(aq)+2e^(-) rarr Cr(s)`,
`DeltaG^(@)= -2xxF xx(-0.9000)=1.8 F` ...(ii)
Adding eq. (i) and (ii)
`Cr^(3+)+3e^(-) rarr Cr(s), DeltaG^(@)=2.224F`
`DeltaG^(@)= -nFE^(@)`
or `E^(@)= -(2.224F)/(3F)= -0.741`V
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