AQA GCSE FOUNDATION Chemistry: Redox Reactions

AQA GCSE Foundation Chemistry: Redox Reactions

What are Redox Reactions?

Redox reactions are chemical reactions that involve the transfer of electrons between reactants. This transfer results in a change in oxidation states of the participating atoms.

Oxidation and Reduction

• Oxidation is the loss of electrons. An atom that is oxidized will have its oxidation state increase.
• Reduction is the gain of electrons. An atom that is reduced will have its oxidation state decrease.

Mnemonic: OIL RIG

• Oxidation Is Loss (of electrons)
• Reduction Is Gain (of electrons)

Identifying Redox Reactions

To identify a redox reaction, we need to look for changes in oxidation states. Here are some common clues:

• The presence of oxygen: Oxygen is a very electronegative element and often gains electrons, causing other atoms to be oxidized.
• The presence of hydrogen: Hydrogen is often oxidized, losing electrons to other atoms.
• The presence of halogens: Halogens like chlorine and bromine can gain electrons, causing other atoms to be oxidized.

Examples

Example 1: The reaction of magnesium with oxygen

2Mg + O2 ? 2MgO

• Magnesium (Mg) is oxidized: It loses electrons and its oxidation state increases from 0 to +2.
• Oxygen (O2) is reduced: It gains electrons and its oxidation state decreases from 0 to -2.

Example 2: The reaction of zinc with hydrochloric acid

Zn + 2HCl ? ZnCl2 + H2

• Zinc (Zn) is oxidized: It loses electrons and its oxidation state increases from 0 to +2.
• Hydrogen (H+) is reduced: It gains electrons and its oxidation state decreases from +1 to 0.

Important Points

• Redox reactions are essential for many processes in our world, including:
  • Respiration
  • Photosynthesis
  • Combustion
  • Rusting
• Redox reactions can be used to generate electricity in batteries and fuel cells.

Practice Questions

1. Identify the oxidation and reduction reactions in the following equation: CuO + H2 ? Cu + H2O
2. Explain how the rusting of iron is a redox reaction.
3. Why is respiration considered a redox reaction?

Key Takeaways

• Redox reactions involve the transfer of electrons.
• Oxidation is the loss of electrons, while reduction is the gain of electrons.
• You can identify redox reactions by looking for changes in oxidation states.
• Redox reactions are fundamental to many important processes.