JEE MAIN - Chemistry (2004 - No. 36)
Consider the following Eo values
$$E_{F{e^{3 + }}/F{e^{2 + }}}^o$$ = 0.77 V;
$$E_{S{n^{2 + }}/S{n}}^o$$ = -0.14 V
Under standard conditions the potential for the reaction
Sn(s) + 2Fe3+(aq) $$\to$$ 2Fe2+(aq) + Sn2+(aq) is :
$$E_{F{e^{3 + }}/F{e^{2 + }}}^o$$ = 0.77 V;
$$E_{S{n^{2 + }}/S{n}}^o$$ = -0.14 V
Under standard conditions the potential for the reaction
Sn(s) + 2Fe3+(aq) $$\to$$ 2Fe2+(aq) + Sn2+(aq) is :
1.68 V
0.63 V
0.91 V
1.40 V
Explanation
$$F{e^{3 + }} + {e^ - } \to F{e^{2 + }}\Delta {G^ \circ }$$
$$\,\,\,\,\,\,\,\,\,\, = - 1 \times F \times 0.77$$
$$S{n^{2 + }} + 2{e^ - } \to Sn\left( s \right)\Delta {G^ \circ }$$
$$ = - 2 \times F\left( { - 0.14} \right)$$
$$Sn\left( s \right) + 2F{e^{3 + }}\left( {aq} \right)$$
$$\,\,\,\,\,\,\,\,\,\, \to 2F{e^{2 + }}\left( {aq} \right) + S{n^{2 + }}\left( {aq} \right)$$
$$\therefore$$ Standard potential for the given reaction
or $$E_{cell}^o = E_{Sn/S{n^{2 + }}}^o + E_{F{e^{3 + }}/F{e^{2 + }}}^0$$
$$ = 0.14 + 0.77 = 0.91\,V$$
$$\,\,\,\,\,\,\,\,\,\, = - 1 \times F \times 0.77$$
$$S{n^{2 + }} + 2{e^ - } \to Sn\left( s \right)\Delta {G^ \circ }$$
$$ = - 2 \times F\left( { - 0.14} \right)$$
$$Sn\left( s \right) + 2F{e^{3 + }}\left( {aq} \right)$$
$$\,\,\,\,\,\,\,\,\,\, \to 2F{e^{2 + }}\left( {aq} \right) + S{n^{2 + }}\left( {aq} \right)$$
$$\therefore$$ Standard potential for the given reaction
or $$E_{cell}^o = E_{Sn/S{n^{2 + }}}^o + E_{F{e^{3 + }}/F{e^{2 + }}}^0$$
$$ = 0.14 + 0.77 = 0.91\,V$$
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