Write the Nernst equation and calculate the e.m.f. of the following cell at 298K.
`Sn_((s))|Sn_((0.050M))^(2+)||H^(+)(0.020M)|H_(2)(1atm//Pt)`
Given `E_(Sn//Sn^(2+))^(@)=-0.14V`
`EMF=(E_(H^(+)//1//2H_(2))^(@)-E_(Sn^(2+)//Sn)^(@))-(0.0591V)/(2)"log"([Sn^(2+)])/([H^(+)]^(2))`.

Explanation

At anode, `Sn rarr Sn^(2+) + 2e^(-)`
At cathode,
`ul(2H^(+) + 2e^(-) rarr 2H_(2))`
`ul(Sn+ 2H^(+) rarr Sn^(2+) + 2H_(2))`
`E= E^(@)- (0.059)/(2)"log" ([H^(+)]^(2))/([Sn^(2+)])`
`=0.14- (0.059)/(2) "log" ([0.05])/([0.02]^(2))`
`=0.14- (0.059)/(2) xx 2.099`
=0.08V