Chemical Reactions and Equations | Class 10 Science Notes

1.2.5 Oxidation and Reduction

Oxidation and reduction are fundamental concepts in chemical reactions involving the gain or loss of oxygen or hydrogen atoms. Oxidation is defined as the gain of oxygen or loss of hydrogen by a substance, while reduction is the loss of oxygen or gain of hydrogen. For example, when copper powder is heated in air, it reacts with oxygen to form black copper(II) oxide (2Cu + O₂ → 2CuO). This is oxidation because copper gains oxygen. Passing hydrogen gas over heated copper oxide causes the oxide to lose oxygen and revert to copper (CuO + H₂ → Cu + H₂O), which is reduction. Simultaneously, hydrogen gains oxygen and is oxidised. Such simultaneous oxidation and reduction reactions are called redox reactions. Other examples include the reaction of zinc oxide with carbon where zinc oxide is reduced to zinc and carbon is oxidised to carbon monoxide (ZnO + C → Zn + CO), and the reaction of manganese dioxide with hydrochloric acid producing manganese chloride, water, and chlorine gas (MnO₂ + 4HCl → MnCl₂ + 2H₂O + Cl₂). In these reactions, substances gaining oxygen or losing hydrogen are oxidised, while those losing oxygen or gaining hydrogen are reduced. Understanding redox reactions is crucial as they occur widely in industrial processes, biological systems, and everyday phenomena such as corrosion and respiration.

📊 Diagram: Figure 1.10 Oxidation of copper to copper oxide; (1.30) showing redox reaction scheme.

🧪 Activity: Activity 1.11: Heating copper powder to observe oxidation to copper oxide and reduction by hydrogen gas.

🔗 Connection: This section leads to understanding the effects of oxidation in everyday life such as corrosion and rancidity.