SPM Chemistry Form 5 Notes – Terminology and Concepts: Oxidation and Reduction (Part 1)

July 9, 2010

Berry Berry Easy would like to present all Berry Readers with one of the most interesting topic (as voted by most students) in SPM Form 5 Chemistry. Without prolonging the suspense, the interesting topic as mentioned by most chemistry takers is “Oxidation and Reduction“. So why is this interesting? Based on a straw poll, it is simply because of the coolness of the word Redox, which is a shorthand for REDuction/OXidation = REDOX!!! Teachers only need to mention this once, and students can remember this virtually forever. Its concept are also rather simple, but at the hardest end (not covered by the syllabus), it can be hard to identify a redox reaction.

One obvious tip to understand redox reactions is to think of them as components of a bigger reaction. So a redox reactions is best imagined as two smallers parts of oxidation and reduction. (If you would like to impress your friends, you can also tell them that, non-redox reactions are called methathesis reactions.)

SPM Chemistry Form 5 – Terminology and Concepts: Oxidation and Reduction (Part 1)

Redox reaction – chemical reactions in which both oxidation and reduction occur simultaneously.

1) Oxidation

• gain of oxygen, O₂ by a substance
• loss of hydrogen, H₂ from a substance
• a loss of electrons
• occurs when there is an increase in oxidation number

2) Reduction

• loss of oxygen, O₂ by a substance
• gain of hydrogen, H₂ from a substance
• a gain of electrons
• occurs when there is an decrease in oxidation number

Oxidation Number – is the charge that the atom of the element would have if complete transfer of electron takes place.

IUPAC nomenclature – name inorganic compounds in order to avoid confusion due to elements have variable oxidation numbers.

Oxidation and Reduction in Terms of Gain and Loss of Oxygen

2CuO (s) + C (s) –> 2Cu (s) + CO₂ (g)

• Reduction:
  CuO loses its oxygen to form copper. CuO (oxidising agent) is being reduced.
• Oxidation:
  Carbon gains oxygen to form CO₂. Carbon (reducing agent) is said to be oxidised.

PbO (s) + CO (g) –> Pb (s) + CO₂ (g)

• Reduction:
  PbO loses its oxygen to form lead. PbO (oxidising agent) is being reduced.
• Oxidation:
  Carbon monoxide (CO) gains oxygen to form CO₂. Carbon monoxide (reducing agent) is said to be oxidised.

H₂ (g) + CuO (s) –> H₂O (l) + Cu (s)

• Reduction:
  CuO loses its oxygen to form copper. CuO (oxidising agent) is being reduced.
• Oxidation:
  Hydrogen (H₂) gains oxygen to form H₂O. Hydrogen (reducing agent) is said to be oxidised.

Oxidation and Reduction in Terms of Gain and Loss of Hydrogen

H₂S (g) + Cl₂ (g) –> S (s) + 2HCl (g)

• Reduction:
  Cl₂ gains hydrogen to form hydrogen chloride. Cl₂ (oxidising agent) is being reduced.
• Oxidation:
  Hydrogen sulphide loses hydrogen to form sulphur. Hydrogen sulphide (reducing agent) is said to be oxidised.

2NH₃ (g) + 3Br₂ (g) –> N₂ (g) + 6HBr (g)

• Reduction:
  Bromine gains hydrogen to form hydrogen bromide. Br₂ (oxidising agent) is being reduced.
• Oxidation:
  Ammonia loses hydrogen to form nitrogen. Ammonia (reducing agent) is said to be oxidised.

Do drop by Berry Berry Easy soon again for the continuation of this interesting chapter.

Please also view the other berry related posts:

1. SPM Chemistry Form 5 Notes – Terminology and Concepts: Oxidation and Reduction (Part 3)
2. SPM Chemistry Form 5 Notes – Terminology and Concepts: Oxidation and Reduction (Part 7)
3. SPM Chemistry Form 5 Notes – Terminology and Concepts: Oxidation and Reduction (Part 4)
4. SPM Chemistry Form 5 Notes – Terminology and Concepts: Oxidation and Reduction (Part 11)
5. SPM Chemistry Form 5 Notes – Terminology and Concepts: Oxidation and Reduction (Part 10)

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