Question

Deducted from the following $E^o$ values of half cells, what combination of two half cells would result in a cell with the largest potential?

(i) $A^{3-}\to A^{2-}+e;E^o=1.5V$

(ii) $B^{2+}+e\to B^{+};E^o=2.1V$

(iii) $C^{2+}+e\to C^{+};E^o=+0.5V$

(iv) $D\to D^{2+}+2e;E^o=-1.5V$

• A. (i) and (iii)
• B. (i) and (ii)
• C. (ii) and (iv)
• D. (iii) and (iv)

Answer 1

Answer: (B)

(i) and (ii)

$A^{3-}\to A^{2-}+e$ $E^o=1.5$

$B^{2+}+e\to B^{+}$ $E^o=2.1$

$C^{2+}+e\to C^{+}$ $E^o=0.5$

$D\to D^{2+}+2e$ $E^o=-1.5$

$1$ & $3\Rightarrow E_o=1.5+0.5=2V$

$1$ & $2\Rightarrow E_o=|1.5+2.1|=3.6V$

$2$ & $4\Rightarrow E_o=(2.1-\frac{1.5}{2})=1.35V$

$3$ & $4\Rightarrow E_o=0.5-1.5=-1V$