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Magnesium and Steam

Magnesium reacts with steam to form magnesium oxide: Mg (s) + H2O (g) → MgO (s) + H2 (g)
The hydrogen is burned as it forms for safety as it is highly flammable.With steam the reaction is much faster than with cold water. Heated magnesium ribbon burns with a bright white flame and a white powder of magnesium oxide is left behind.
In the laboratory, mineral wool soaked in water is placed at the closed end of a boiling tube and a coil of magnesium ribbon is placed further along. The magnesium is heated strongly, then the wool is warmed so that steam passes over the hot metal. The hydrogen leaves through a delivery tube and is lit at the end of it.Compare this with cold water. Magnesium reacts very slowly with cold water to form magnesium hydroxide, and only a few bubbles of hydrogen are seen. With steam the product is the oxide, because magnesium hydroxide is not stable at such a high temperature.This is a redox reaction. Magnesium is oxidised from 0 to +2, and hydrogen is reduced from +1 in water to 0 in H2. Magnesium is the reducing agent.

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Specification: Edexcel Chemistry (8CH0), AS-level, Topic 4A: The elements of Groups 1 and 2. Topic: Group 2.

Key terms in this lesson

reducing agent
A substance that donates electrons to another species, causing it to be reduced, while it is itself oxidised.
redox reaction
A reaction in which oxidation and reduction happen together, with electrons transferred between the species involved.

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