Consider the following half-cell reactions. Al(s) \(\to\) Al3+(aq) + 3e- Cu2+(aq) + 2e- \(\to\) Cu(s)...

WAEC 2016

Consider the following half-cell reactions.
Al_(s) \(\to\) Al³⁺_(aq) + 3e^-
Cu²⁺_(aq) + 2e^- \(\to\) Cu_(s)

The overall equation for the reaction is

A. Al_(s) + Cu²⁺_(aq) \(\to\) Al³⁺_(aq) + Cu_(s)
B. 2Al_(s) + Cu²⁺_(aq) \(\to\) 2Al_(aq) + Cu_(s)
C. 2Al_(s) + 3Cu²⁺_(aq) \(\to\) 3Cu_(s) + 2Al³⁺_(aq)
D. 3Al_(s) + 2Cu²⁺_(aq) \(\to\) Cu_(s) + 3Al³⁺_(aq)

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Correct Answer: Option 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)

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