Question

Using the standard electrode potentials given in Table 3.1, predict if the reaction between the following is feasible:
(i) Fe3+ (aq) and I- (aq)
(ii) Ag+ (aq) and Cu(s)
(iii) Fe3+(aq) and Br-(aq)
(iv) Ag(s) and Fe3+(aq)
(v) Br2 (aq) and Fe2+(aq).

Answer 1

(i) Fe3+(aq) + e- $\rightarrow$ Fe2+(aq) ] × 2; $E^0$= +0.77 V
2I-(aq) $\rightarrow$ I2(s) + 2e- ; $E^0$= -0.54 V

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2 Fe3+(aq) + 2I-(aq) $\rightarrow$ 2Fe2+(aq) + I2(s) ; $E^0$ = +0.23 V

Since$E^0$ for the overall reaction is positive, the reaction between Fe3+(aq and I-(aq) is feasible.

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(ii) Ag+(aq) + e- → Ag(s) ] × 2 ; $E^0$= +0.80 V
Cu(s) → Cu2+(aq) + 2e- ; $E^0$= -0.34 V

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2Ag+(aq)+ Cu(s) → 2Ag(s) + Cu2+(aq) ; $E^0$ = +0.46 V
Since $E^0$ for the overall reaction is positive, the reaction between Ag+(aq) and Cu(s) is feasible

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(iii) Fe3+(aq)+e- → Fe2+(aq) ] × 2 ; $E^0$ = +0.77 V
2Br-(aq) → Br2(l) + 2e- ; $E^0$= -1.09 V

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Since $E^0$ for the overall reaction is negative, the reaction between Fe3+(aq) and Br-(aq)is not feasible

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Ag(s) $\rightarrow$ Ag+(aq) + e- ; $E^0$ = -0.80 V
Fe3+(aq) + e- $\rightarrow$ Fe2+(aq) ; $E^0$ = +0.77 V

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Ag(s) + Fe3+(aq) $\rightarrow$ Ag+(aq) + Fe2+(aq) ; $E^0$ = -0.03 V
Since $E^0$ for the overall reaction is negative, the reaction between Ag(s) and Fe3+(aq) is not feasible.

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(v) Br2(aq) +2e- → 2Br-(aq) ;$E^0$ = +1.09 V
Fe2+(aq) → Fe3+(aq) + e- ] × 2 ; $E^0$ = - 0.77 V

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Br2(aq) + 2Fe2+(aq) → 2Br-(aq) +2Fe3+(aq) ;$E^0$ = +0.32 V

Since$E^0$ for the overall reaction is positive, the reaction between Br2(aq) and Fe2+(aq) is feasible.