Predict whether zinc and silver react with 1 M sulphuric acid to give out hydrogen or not.
Given that the standard potentials of zinc and silver are –0.76 volt and +0.80 volt respectively.
(a) Reaction of zinc with sulphuric acid:
Zn + H2SO4 ⟶ ZnSO4 + H2
i.e., Zn + 2H+ ⟶ Zn2+ + H2
Cell representation: Zn | Zn2+ || H+ | H2
E°cell = E°(H+/H2) − E°(Zn2+/Zn)
= 0 − (−0.76) = +0.76 V
Since EMF is positive, the reaction takes place.
(b) Reaction of silver with sulphuric acid:
2Ag + H2SO4 ⟶ Ag2SO4 + H2
i.e., 2Ag + 2H+ ⟶ 2Ag+ + H2
Cell representation: Ag | Ag+ || H+ | H2
E°cell = E°(H+/H2) − E°(Ag+/Ag)
= 0 − 0.80 = −0.80 V
Since EMF is negative, the reaction does not take place.