Question

Using the standard electrode potentials given in table 8.1 (NCERT), 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)

Answer 1

i)

           $[{ Fe }^{ 3+ }(aq) + { e }^{ - } \rightarrow { Fe }^{ 2+ }(aq)] \times 2 \Longrightarrow { E }^{ o } = +0.77 V$

           $2{ I }^{ - }(aq) \rightarrow { I }_{ 2 }(s) + 2{ e }^{ - } \Longrightarrow { E }^{ o } = -0.54 V$

           $2{ Fe }^{ 3+ } (aq) + 2{ I }^{ - }(aq) \rightarrow 2{ Fe }^{ 2+ }(aq) + { I }_{ 2 }(s) \Longrightarrow { E }^{ o } = +0.23 V$

The electrode potential value of the reaction is positive.

Therefore, the reaction is feasible.

ii)

            $Ag^{ + }(aq) + { e }^{ - } \rightarrow Ag(s) \Longrightarrow { E }^{ o } = +0.80 V$

            $Cu(s) \rightarrow { Cu }^{ 2+ }(aq) + 2{ e }^{ - } \Longrightarrow { E }^{ o }$

            $= -0.34 V$

            $2{ Ag }^{ + } (aq) + Cu(s) \rightarrow  2Ag(s) + C{ u }^{ 2+ }(aq) \Longrightarrow  { E }^{ o }$

            = +0.46 V

The electrode potential value of the reaction is positive.

Therefore, the reaction is feasible.

iii)

             $[{ Fe }^{ 3+ }(aq) + { e }^{ - } \rightarrow { Fe }^{ 2+ }(aq)] \times 2 \Longrightarrow { E }^{ o }$

             = +0.77 V

             $2{ Br }^{ - }(aq) \rightarrow { Br }_{ 2 }(s) + 2{ e }^{ - } \Longrightarrow { E }^{ o }$

             = -1.09 V$2{ Fe }^{ 3+ } (aq) + 2{ Br }^{ - }(aq) \rightarrow 2{ Fe }^{ 2+ }(aq) + { Br }_{ 2 }(l) \Longrightarrow { E }^{ o } = -0.32 V$

The electrode potential value of the reaction is negative.

Therefore, the reaction is not feasible.

iv)

$\quad Ag(s)\quad \rightarrow \quad A{ g }^{ + }(aq)\quad +\quad { e }^{ - }\quad \Longrightarrow \quad { E }^{ o }\quad =\quad -0.80\quad V$

$F{ e }^{ 3+ }(aq)\quad +\quad { e }^{ - }\quad \rightarrow \quad Fe^{ 2+ }(aq)\quad \Longrightarrow \quad { E }^{ o }\quad \quad =\quad +0.77\quad V$

$Ag(s)\quad \quad +\quad F{ e }^{ 3+ }(aq)\quad \rightarrow \quad A{ g }^{ + }\quad +\quad F{ e }^{ 2+ }(aq)\quad \Longrightarrow \quad { E }^{ o }\quad =\quad -0.03\quad V$

The electrode potential value of the reaction is negative.

Therefore, the reaction is not feasible.

v)

$\quad { Br }_{ 2 }(l)\quad +\quad { 2e }^{ - }\quad \rightarrow \quad 2Br^{ - }(aq)\quad \Longrightarrow \quad { E }^{ o }\quad =\quad +1.09\quad V$

$\quad \quad F{ e }^{ 2+ }(aq)\quad \rightarrow \quad Fe^{ 3+ }(aq)+\quad { e }^{ - }]\quad \times \quad 2\quad \Longrightarrow \quad { E }^{ o }\quad =\quad -0.77\quad V$

${ Br }_{ 2 }(aq)\quad +\quad 2F{ e }^{ 2+ }(aq)\quad \rightarrow \quad 2Br^{ - }(aq)\quad +\quad 2F{ e }^{ 3+ }(aq)\quad \Longrightarrow \quad { E }^{ o }\quad =\quad +0.32\quad V$

The electrode potential value of the reaction is positive.

Therefore, the reaction is feasible.

Answer 2

i)

[{ Fe }^{ 3+ }(aq) + { e }^{ - } \rightarrow { Fe }^{ 2+ }(aq)] \times 2 \Longrightarrow { E }^{ o } = +0.77 V[Fe

3+

(aq)+e

−

→Fe

2+

(aq)]×2⟹E

o

=+0.77V

2{ I }^{ - }(aq) \rightarrow { I }_{ 2 }(s) + 2{ e }^{ - } \Longrightarrow { E }^{ o } = -0.54 V2I

−

(aq)→I

2

(s)+2e

−

⟹E

o

=−0.54V

2{ Fe }^{ 3+ } (aq) + 2{ I }^{ - }(aq) \rightarrow 2{ Fe }^{ 2+ }(aq) + { I }_{ 2 }(s) \Longrightarrow { E }^{ o } = +0.23 V2Fe

3+

(aq)+2I

−

(aq)→2Fe

2+

(aq)+I

2

(s)⟹E

o

=+0.23V

The electrode potential value of the reaction is positive.

Therefore, the reaction is feasible.

ii)

Ag^{ + }(aq) + { e }^{ - } \rightarrow Ag(s) \Longrightarrow { E }^{ o } = +0.80 VAg

+

(aq)+e

−

→Ag(s)⟹E

o

=+0.80V

Cu(s) \rightarrow { Cu }^{ 2+ }(aq) + 2{ e }^{ - } \Longrightarrow { E }^{ o }Cu(s)→Cu

2+

(aq)+2e

−

⟹E

o

= -0.34 V=−0.34V

= +0.46 V

The electrode potential value of the reaction is positive.

Therefore, the reaction is feasible.

iii)

[{ Fe }^{ 3+ }(aq) + { e }^{ - } \rightarrow { Fe }^{ 2+ }(aq)] \times 2 \Longrightarrow { E }^{ o }[Fe

3+

(aq)+e

−

→Fe

2+

(aq)]×2⟹E

o

= +0.77 V

2{ Br }^{ - }(aq) \rightarrow { Br }_{ 2 }(s) + 2{ e }^{ - } \Longrightarrow { E }^{ o }2Br

−

(aq)→Br

2

(s)+2e

−

⟹E

o

= -1.09 V2{ Fe }^{ 3+ } (aq) + 2{ Br }^{ - }(aq) \rightarrow 2{ Fe }^{ 2+ }(aq) + { Br }_{ 2 }(l) \Longrightarrow { E }^{ o } = -0.32 V2Fe

3+

(aq)+2Br

−

(aq)→2Fe

2+

(aq)+Br

2

(l)⟹E

o

=−0.32V

The electrode potential value of the reaction is negative.

Therefore, the reaction is not feasible.

iv)

\quad Ag(s)\quad \rightarrow \quad A{ g }^{ + }(aq)\quad +\quad { e }^{ - }\quad \Longrightarrow \quad { E }^{ o }\quad =\quad -0.80\quad VAg(s)→Ag

+

(aq)+e

−

⟹E

o

=−0.80V

F{ e }^{ 3+ }(aq)\quad +\quad { e }^{ - }\quad \rightarrow \quad Fe^{ 2+ }(aq)\quad \Longrightarrow \quad { E }^{ o }\quad \quad =\quad +0.77\quad VFe

3+

(aq)+e

−

→Fe

2+

(aq)⟹E

o

=+0.77V

Ag(s)\quad \quad +\quad F{ e }^{ 3+ }(aq)\quad \rightarrow \quad A{ g }^{ + }\quad +\quad F{ e }^{ 2+ }(aq)\quad \Longrightarrow \quad { E }^{ o }\quad =\quad -0.03\quad VAg(s)+Fe

3+

(aq)→Ag

+

+Fe

2+

(aq)⟹E

o

=−0.03V

The electrode potential value of the reaction is negative.

Therefore, the reaction is not feasible.

v)

\quad { Br }_{ 2 }(l)\quad +\quad { 2e }^{ - }\quad \rightarrow \quad 2Br^{ - }(aq)\quad \Longrightarrow \quad { E }^{ o }\quad =\quad +1.09\quad VBr

2

(l)+2e

−

→2Br

−

(aq)⟹E

o

=+1.09V

\quad \quad F{ e }^{ 2+ }(aq)\quad \rightarrow \quad Fe^{ 3+ }(aq)+\quad { e }^{ - }]\quad \times \quad 2\quad \Longrightarrow \quad { E }^{ o }\quad =\quad -0.77\quad VFe

2+

(aq)→Fe

3+

(aq)+e

−

]×2⟹E

o

=−0.77V

{ Br }_{ 2 }(aq)\quad +\quad 2F{ e }^{ 2+ }(aq)\quad \rightarrow \quad 2Br^{ - }(aq)\quad +\quad 2F{ e }^{ 3+ }(aq)\quad \Longrightarrow \quad { E }^{ o }\quad =\quad +0.32\quad VBr

2

(aq)+2Fe

2+

(aq)→2Br

−

(aq)+2Fe

3+

(aq)⟹E

o

=+0.32V

The electrode potential value of the reaction is positive.

Therefore, the reaction is feasible.