Define oxidation in terms of: (a) loss of electrons (b) an increase in oxidation number

Chemical Reactions – Redox

What is Oxidation?

Oxidation is the process where a substance loses electrons or its oxidation number increases. Think of electrons as tiny coins: when you give away coins, you lose them.

  • Loss of electrons: The atom or ion gives up one or more electrons.

  • Increase in oxidation number: The charge on the atom becomes more positive.

Analogy: The Electron Bank

Imagine each atom has an electron bank account. When it deposits electrons, its oxidation number goes down (reduction). When it withdraws electrons, its oxidation number goes up (oxidation). 💰⚡️

Example 1: Sodium

In the reaction:

\$\,\ce{Na -> Na+ + e-}\,\$

Sodium starts with oxidation number 0. After losing one electron, it becomes \$\ce{Na+}\$ with oxidation number +1.

So, oxidation = loss of an electron = increase in oxidation number.

Example 2: Iron(III) Oxide

During the reduction of iron(III) oxide:

\$\,\ce{Fe2O3 + 3e- -> 2Fe + 3O^{2-}}\,\$

Iron goes from +3 to 0 (gains electrons, reduction). Oxygen goes from -2 to 0 (loses electrons, oxidation).

AtomInitial Oxidation No.After OxidationChange
Na0+1+1 (loss of 1 e⁻)
O in \$\ce{Fe2O3}\$-20+2 (loss of 2 e⁻)

Exam Tip 🚀

When you see a redox problem:

  1. Identify which species is gaining electrons (reduction) and which is losing electrons (oxidation).

  2. Check the change in oxidation numbers – the one that increases is oxidised.

  3. Remember: Oxidation = loss of electrons = increase in oxidation number.

Use the “electron bank” analogy to keep the concept clear in your mind. Good luck! 🍀