# Oxidation and reduction by electrons

> Oxidation without oxygen


## Objectives

- Define oxidation as loss of electrons (oxidation state increases) and reduction as gain of electrons (oxidation state decreases).
- Identify what is oxidized and reduced in a reaction with no oxygen.
- Identify the oxidizing agent (it is reduced) and the reducing agent (it is oxidized).

## 1. Properties of iron




## 2. Oxidation without oxygen?

Predict: what happened to the iron ion?

- Nothing: without oxygen it cannot be oxidation
- It gained one electron
- It lost one electron ✓

Going from $\ce{Fe^{2+}}$ to $\ce{Fe^{3+}}$, the ion loses one electron. Oxidation is loss of electrons, so this is oxidation even without oxygen.

[ar-EG] لما الـ $\ce{Fe^{2+}}$ يتحوّل لـ $\ce{Fe^{3+}}$ بيفقد electron واحد. والـ oxidation هو فقد electrons، فده oxidation حتى من غير oxygen.
## 3. Oxidation: loss of electrons

Remember: you met oxidation as gain of oxygen. Here is a wider meaning. Oxidation A process in which an atom or ion loses electrons, so its oxidation state increases. Loses one electron: +2 → +3 Gaining oxygen is one case of this. In MgO, Mg has lost two electrons to oxygen: 0 → +2.


## 4. Reduction: gain of electrons

Reduction A process in which an atom or ion gains electrons, so its oxidation state decreases. Gains two electrons: +2 → 0 The two happen together. Electrons lost by one substance are gained by another. Memory aid OIL RIG: Oxidation Is Loss, Reduction Is Gain (of electrons).


## 5. Worked: zinc in copper sulphate

Step 1: Oxidation states Zn: 0 → +2. Cu: +2 → 0. The $\ce{SO4}$ group stays −2. Step 2: Who lost, who gained? Zn lost 2 electrons: it is oxidized. $\ce{Cu^{2+}}$ gained 2 electrons: it is reduced. Step 3: The agents Zn is the reducing agent: it is itself oxidized. $\ce{CuSO4}$ is the oxidizing agent: it is itself reduced. Oxidation always needs oxygen.


## 6. Your turn

In $\ce{2Na + Cl2 -> 2NaCl}$, which is the oxidizing agent?

- Na
- None: no oxygen is involved
- NaCl
- $\ce{Cl2}$ ✓

Na: 0 → +1 (oxidized, reducing agent). Cl: 0 → −1 (reduced, oxidizing agent).

[ar-EG] الـ Na: من 0 → +1 (oxidized، يعني هو الـ reducing agent). الـ Cl: من 0 → −1 (reduced، يعني هو الـ oxidizing agent).
## 7. Summary

Oxidation: loss of electrons; the oxidation state increases. Reduction: gain of electrons; the oxidation state decreases. The oxidizing agent gains electrons (it is reduced). The reducing agent loses electrons (it is oxidized). Back to the hook: $\ce{Fe^{2+} -> Fe^{3+} + e-}$ is oxidation. Next lesson: why it happens so easily. Can you explain why $\ce{Cl2}$ is an oxidizing agent, though no oxygen is involved? In $\ce{2Na + Cl2 -> 2NaCl}$, chlorine gains electrons (0 → −1), so it is reduced. The substance that gains electrons is the oxidizing agent, with or without oxygen.



Chapter: Transition Elements (https://yaani.ai/ar/learn/chemistry/chem-s3-en.ch1)
Source: https://yaani.ai/ar/lesson/chem-s3-en.lesson-redox.electronic