A zinc electrode is placed in `0.1M` solution of `ZnSO_(4)` at `25^(@)C`. Assuming salt is dissociated to the extent of `20%` at this dilution. The potential of this electrode at this temperature is `:`
`(E^(c-)._(Zn^(2+)|Zn)=-0.76V)`
`a. 0.79V" ".b. -0.79V" "c. -0.81V." "d. 0.81V`

Options

A. `-0.81 V`
B. `-0.79 V`
C. `0.81 V `
D. `0.79 V`

Answer

A

Explanation

The electrode reaction is :
`Zn^(2+) (aq) + 2e^(-) to Zn (s)`
`E = E^(@) - (0.059)/(2) "log" (1)/([Zn^(2+)])`
` [Zn^(2+)] = 0.1 xx (20)/(100) = 0.02 M , E^(@) = -0.76 V `
`therefore E = -0.76 - (0.059)/(2) log (1)/(0.02)`
`= -0.76 - (0.059)/(2) log 50`
`= -0.76 - (0.059)/(2) xx 1.70`
`= -0.76 -0.05 = -0.81 V `