Write the Nernst equation and calculate the e.m.f. of the following cells at 298  K.

(i) Mg (s) | Mg²⁺ (0.001 M) | | Cu²⁺ (0.001 M) | Cu (s)           

(ii) Fe (s) | Fe²⁺ (0.001 M) | | H⁺ (1 M) | H₂ (g) (1 bar) | Pt (s)

(iii) Sn (s) | Sn²⁺ (0.050 M) | | H⁺ (0.020 M) | H₂ (g) (1 bar) | Pt (s)

(iv) Pt (s) | Br₂ (l) | Br^– (0.010 M) | | H⁺ (0.030 M) | H₂ (g) (1 bar) | Pt (s)

Given Eº_Mg²⁺_/Mg = 2.37 V, Eº_Cu²⁺_/Cu = +0.34 V, Eº_Fe²⁺ _Fe = – 0.44 V, Eº_Sn²⁺_/Sn = – 0.14 V, Eº_{1/2 Br2/ Br}– = + 1.08 V.