Oxidation

In simple terms, oxidation is the gain of oxygen.

We can say that magnesium is oxidised as it becomes magnesium oxide when it is burned in the air.

Oxidation can also be considered as part of a pair of changes that go at the same time: reduction and oxidation (redox). Reduction can be considered as the removal of oxgen from a substance. Metal oxides can be reduced to give the metal.

When one substance is oxidised, another is reduced.

Flash Powder Experiment

Magnesium metal burns releasing heat and light and producing magnesium oxide. When magnesium is mixed with potassium chlorate it forms flash powder used in fireworks, flares and originally in flash photography. A huge photograph is taken of the class by standing them against specially treated light-sensitive paper. The paper is coated with a silver halide, a compound of silver and a group 7 halogen. When the paper is exposed to a bright light the silver halide is reduced to silver metal and so then appears darker around where the students were standing.

Exam Tip: Questions concerning metal-halogen compounds are common in exams, particularly those related to the electrolysis of sodium chloride solution (brine). Practise naming the products at each electrode and the uses of those materials. Remember the main use of silver halides is in the making of photographic film and photographic paper.

Example Exam Questions:

• Explain why the halogens, Chlorine, Bromine and Iodine form 1- ions when they react with metals.
• The melting points of Sodium and Chlorine are 98°C and -101°C respectively. Explain why the melting point of Sodium Chloride is 801°C.