Consider the following half-cell reactions.
Al
(s) \(\to\) Al
3+(aq) + 3e
-Cu
2+(aq) + 2e
- \(\to\) Cu
(s)The overall equation for the reaction is
A. Al
(s) + Cu
2+(aq) \(\to\) Al
3+(aq) + Cu
(s)B. 2Al
(s) + Cu
2+(aq) \(\to\) 2Al
(aq) + Cu
(s)C. 2Al
(s) + 3Cu
2+(aq) \(\to\) 3Cu
(s) + 2Al
3+(aq) 
D. 3Al
(s) + 2Cu
2+(aq) \(\to\) Cu
(s) + 3Al
3+(aq) Correct Answer: C
Explanation
Al(s) \(\to\) Al3+(aq) + 3e- ______(i)
Cu2+(aq) + 2e- \(\to\) Cu(s) ________(ii)
To balance the electrons, multiply equation (i) by 2 and equation (ii) by 3 and then add the resulting equations
2Al(s) \(\to\)2Al3+(aq) + 3e-
3cu2+(aq) + 6e- \(\to\)3Cu(s)
2Al(s) + 3Cu2+(aq) \(\to\) 3Cu(s) + 2Al3+(aq)
