Question

Why cannot oxidation occur without reduction?

Answer 1

1. Oxidation is defined as a reaction that involves the loss of electrons by an atom or a group of atoms.
2. Reduction is defined as a reaction that involves the gain of electrons by an atom or a group of atoms.
3. Oxidation and reduction are coupled processes i.e. one cannot happen without the other.
4. This is because electrons can neither be created nor destroyed throughout a reaction. When one chemical species loses electrons (oxidation), those electrons have to be gained by another chemical species (reduction).
5. Consider the reaction:

$$\begin{gathered} \mathrm{Zn}\left(\mathrm{s}\right)+{\mathrm{CuSO}}_4\left(\mathrm{aq}\right)\to {\mathrm{ZnSO}}_4\left(\mathrm{aq}\right)+\mathrm{Cu}\left(\mathrm{s}\right) \\ \left(\mathrm{Zinc}\right)(\mathrm{Copper}(\mathrm{Zinc}\left(\mathrm{Copper}\right) \\ \mathrm{sulphate})\mathrm{sulphate}) \end{gathered}$$

Copper is present in Copper sulfate as ${\mathrm{Cu}}^{2+}$ and Zinc is present in Zinc sulphate as ${\mathrm{Zn}}^{2+}$. The ionic form of the above reaction would be

$\mathrm{Zn}\left(\mathrm{s}\right)+{\mathrm{Cu}}^{2+}\left(\mathrm{aq}\right)\to {\mathrm{Zn}}^{2+}\left(\mathrm{aq}\right)+\mathrm{Cu}\left(\mathrm{s}\right)$

6. In the ionic reaction, it can be seen that Zinc is losing 2 electrons to become ${\mathrm{Zn}}^{2+}$i.e. Zinc is getting oxidised. It can also be seen that Copper is gaining the two electron lost by Zinc and is getting converted from ${\mathrm{Cu}}^{2+}$ to $\mathrm{Cu}$ i.e. Copper is getting reduced. Both processes are occurring simultaneously.

7. Oxidation cannot occur without reduction because the electrons lost by one species has to be gained by another.