Set up a cell consisting of Mg∣MgSO4(1M)
as one electrode (
by dipping a magnesium rod in 1MMgSO4
solution )
and standard hydrogen electrode Pt,(1atm)H⊕∣(1M)
as the second electrode and measure the EMF
of the cell. Also note the direction of deflection in the voltmeter. The direction of deflection shows that electrons flow from magnesium electrode to hydrogen electrode, i.e.,
oxidation takes place on magnesium electrode and reduction on hydrogen electrode. Hence, the cell may be represented as follows :
Mg|Mg2+(1M)||H⊕(1M)||H⊕(1M)|H2,(1atm),Pt
E
c-
cell
=Ec-_((H⊕∣H2))-E
c-
(Mg2+∣Mg)
Put E
c-
H⊕∣H2
=0
Hence, E
c-
Mg2+∣Mg
=-E
c-
cell