Ncert Exercises & Solutions

8.26 : Using the standard electrode potentials given in the Table 8.1, predict if the reaction between the following is feasible:
(a) ${Fe}^{3 +}$ (aq) and $I^{-}$ (aq)
(b) ${Ag}^{+}$ (aq) and Cu(s)
(c) ${Fe}^{3 +}$ (aq) and Cu(s)
(d) Ag(s) and ${Fe}^{3 +}$ (aq)
(e) ${Br}_{2} (aq)$ and ${Fe}^{2 +}$ (aq)

NEETprep Answer:

(a) The possible reaction between

{Fe}_{(aq)}^{3 +} + {l^{-}}_{(aq)}

2 {Fe}^{3 -}_{(aq)} + 2 {l^{-}}_{(aq)} \to 2 {Fe}^{2 +}_{(aq)} + l_{2 (s)}

is given by,

Oxidation half equation :

2 {l^{-}}_{(aq)} \to l_{2 (s)} + 2 e^{-} : E ° = - 0.54 V

\frac{Reduction half equation : [{Fe}^{3 +}_{(aq)} + e^{-} \to {Fe}^{2 -}_{(aq)}] \times 2; E ° = + 0.77 V}{2 {Fe}^{3 +}_{(aq)} + 2 {l^{-}}_{(aq)} \to 2 {Fe}^{2 +}_{(aq)} + I_{2 (s)}; E ° = + 0.23 V}

E °

for the overall reaction is positive. Thus, the reaction between

{Fe}^{3 +}_{(aq)} and {I^{-}}_{(aq)}

is feasible.

(b) The possible reaction between

{Ag}^{+}_{(aq)} + {Cu}_{(s)}

is given by,

2 {Ag}^{+}_{(aq)} + {Cu}_{(s)} \to 2 {Ag}_{(s)} + {Cu}^{2 +}_{(aq)}

Oxidation half equation :

{Cu}_{(s)} \to {Cu}^{2 +}_{(aq)} + 2 e^{-} : E ° = - 0.34 V

\frac{Reduction half equation : [{Ag}^{+}_{(aq)} + e^{-} \to {Ag}_{(s)}] \times 2; E ° = + 0.80 V}{2 {Ag}^{+}_{(aq)} + {Cu}_{(s)} \to 2 {Ag}_{(s)} + {Cu}^{2 +}; E ° = + 0.46 V}

E °

positive for the overall reaction is positive. Hence, the reaction between

{Ag}^{+}_{(aq)} and {Cu}_{(s)}

is feasible.

{F e^{3 +}}_{(aq)} and {Cu}_{(s)}

is given by,

2 {Fe}^{3 +}_{(aq)} + {Cu}_{(s)} \to 2 {Fe}^{2 +}_{(s)} + {Cu}^{2 +}_{(aq)}

Oxidation half equation :

{Cu}_{(s)} \to {Cu}^{2 +}_{(aq)} + 2 e^{-}; E ° = - 0.34 V

\frac{Reduction half equation : [{Fe}^{3 +}_{(aq)} + e^{-} \to {Fe}^{2 +}_{(s)}] \times 2; E ° = + 0.77 V}{2 {Fe}^{3 +}_{(aq)} + {Cu}_{(s)} \to 2 {Fe}^{2 +}_{(s)} + {Cu}^{2 +}_{(aq)}; E ° = + 0.43 V}

E °

positive for the overall reaction is positive. Hence, the reaction between

{Fe}^{3 +}_{(aq)} and {Cu}_{(s)}

is feasible.

(d) The possible reaction between

A g_{(s)} a n d {Fe}^{3 +}_{(aq)}

{Ag}_{(s)} + 2 {Fe}^{3 +}_{(aq)} \to {Ag}^{+}_{(aq)} + {Fe}^{2 +}_{(aq)}

is given by,

Oxidation half equation :

{Ag}_{(s)} \to {Ag}^{+}_{(aq)} + e^{-}; E ° = - 0.80 V

\frac{Reduction half equation : {Fe}^{3 +}_{(aq)} + e^{-} \to {Fe}^{2 +}_{(aq)}; E ° = + 0.77 V}{{Ag}_{(s)} + {Fe}^{3 +}_{(aq)} \to {Ag}^{+}_{(aq)} + {Fe}^{2 +}_{(aq)}; E ° = - 0.03 V}

Here,

E °

for the overall reaction is negative. Hence, the reaction between

A g_{(s)} a n d {Fe}^{3 +}_{(aq)}

is not feasible.

(e) The possible reaction between

{Br}_{2 (aq)} and {Fe}^{2 +}_{(aq)}

is given by,

{Br}_{2 (s)} + 2 {Fe}^{2 +}_{(aq)} \to 2 {Br}^{-}_{(aq)} + 2 {Fe}^{3 +}_{(aq)}

Oxidation half equation :

{Fe}^{2 +}_{(aq)} \to {Fe}^{3 +}_{(aq)} + e^{-}] \times 2; E ° = - 0.77

\frac{Reduction half equation : {Br}_{2 (aq)} + 2 e^{-} \to 2 {Br}^{-}_{(aq)}; E ° = + 1.09 V}{{Br}_{2 (aq)} + 2 {Fe}^{2 +}_{(aq)} \to 2 {Br}^{-}_{(aq)} + 2 {Fe}^{3 +}_{(aq)}; E ° = - 0.32 V}

Here,

E °

for the overall reaction is positive. Hence, the reaction between

{Br}_{2 (aq)} and {Fe}^{2 +}_{(aq)}

is feasible.

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