Question

Using standard reduction potentials (Appendix E), calculate the standard emf for each of the following reactions:

(a) Cl₂ (g) + 2I^- _(aq)→ 2Cl^- _(aq)+ I_2(s)

(b) Ni(s) + 2 Ce⁴⁺(aq) →Ni²⁺(aq) + 2 Ce³⁺(aq)

(c) Fe(s) + 2 Fe³⁺(aq)→3 Fe²⁺(aq)

(d) 2 NO₃^-(aq) + 8 H⁺(aq) + 3 Cu(s)→ 2NO(q) + 4H₂O(l) + 3 Cu²⁺(aq)

One Class Solution:-

a)CI₂(g) +2e-→2Cl^-(aq) E^o = 1.359 V

2I^- _(aq)→+ I_2(s)+ 2e- E^o = 0.536 V, E⁰= 1.359-0.536=0.823V

b) Ni(s) →Ni²⁺(aq) + 2e- anode E^o = –0.28V

2[Ce⁴⁺(aq) +e- →2 Ce³⁺(aq)] cathode E^o =1.61 V

E^o = 1.61-(-0.28)=1.89 V

c) Fe(s) + 2 Fe³⁺(aq)→3 Fe²⁺(aq) E^o =?

Fe(s) → Fe²⁺(aq) +2e- E^o = -0.440V

Fe³⁺(aq) +e- → Fe²⁺(aq) E^o = 0.771V

E=0.771-(-0.440)= 1.211 V

(d) 2 NO₃^-(aq) + 8 H⁺(aq) + 3 Cu(s)→ 2NO(q) + 4H₂O(l) + 3 Cu²⁺(aq)

2 NO₃^-(aq) + 8 H⁺(aq) + 3e-→ 2NO(q) + 4H₂O(l) E^o = 0.96V

Cu(s)→ Cu²⁺(aq) +2e- E^o = V+0.377

E^o =0.96-0.377= 0.583V