# Oxidation and reduction by oxygen

> Gain and loss of oxygen, and the agents that cause them


## Objectives

- Define oxidation as gain of oxygen (or loss of hydrogen) and reduction as loss of oxygen (or gain of hydrogen).
- Identify the oxidizing agent and the reducing agent in a reaction.
- Explain that the oxidizing agent is itself reduced, and the reducing agent is itself oxidized.

## 1. Properties of iron




## 2. Black, then pink again

Predict: what did the hydrogen do to the black solid?

- It just cleaned off soot
- It took oxygen away from it ✓
- It added hydrogen to the copper

The black solid is copper (II) oxide, formed when copper gained oxygen from the air in the flame. Heating it in hydrogen took that oxygen away, so the copper came back.

[ar-EG] الجسم الأسود هو الـ copper (II) oxide، واتكوّن لما الـ copper كسب oxygen من الهوا في اللهب. ولما اتسخّن في الـ hydrogen، الـ hydrogen شال منه الـ oxygen ده، فالـ copper رجع.
## 3. Oxidation

Oxidation Gain of oxygen, or loss of hydrogen. Copper gains oxygen: copper is oxidized Burning and rusting are oxidation too: a substance gains oxygen.


## 4. Reduction

Reduction Loss of oxygen, or gain of hydrogen. Oxidation and reduction happen together. Here $CuO$ loses oxygen while $H_2$ gains it.


## 5. The two agents

$H_2$ takes the oxygen: it is the **reducing agent**. $CuO$ gives the oxygen: it is the **oxidizing agent**. The oxidizing agent is the substance that gets oxidized. Contrast: $H_2$ is oxidized to water, yet we call it the reducing agent.


## 6. New reactions

In $\ce{2Mg + CO2 -> 2MgO + C}$, which substance is the reducing agent? In $\ce{Fe2O3 + 2Al ->[\Delta] Al2O3 + 2Fe}$, what happens to aluminum? In $\ce{H2S + Cl2 -> 2HCl + S}$, $H_2S$ loses hydrogen, so $H_2S$ is ___.


## 7. Summary

Oxidation: gain of oxygen or loss of hydrogen. Reduction: loss of oxygen or gain of hydrogen. The oxidizing agent supplies oxygen and is itself reduced. The reducing agent (e.g. $H_2$, CO, C) takes oxygen away and is itself oxidized. The hook, step by step: oxidation, then reduction. Back to the hook: the flame oxidized copper to CuO; hydrogen, the reducing agent, reduced it back. Key words: **oxidation**, **reduction**, **oxidizing agent**, **reducing agent**. Can you explain why CO is called a reducing agent, although it is oxidized?



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