Why steam is used

Magnesium reacts only very slowly with cold water, so steam is used to demonstrate its reactivity clearly. Steam contacts hot magnesium, producing magnesium oxide and hydrogen.

Equation and observations

Mg + H2O(g) -> MgO + H2. Magnesium may glow brightly, a white solid forms and hydrogen is collected. The state symbol (g) is important because the reactant is steam.

Redox interpretation

Magnesium loses two electrons to form Mg2+ within magnesium oxide. Hydrogen in water gains electrons and forms H2. The reaction therefore confirms magnesium is above hydrogen.

Apparatus reasoning

Water is heated first to generate steam, which passes over magnesium. Hydrogen must be allowed to displace air before testing to avoid an explosive air–hydrogen mixture.

High-value recall and connections

Essential recall: Write the equation for magnesium with steam. Mg + H2O(g) -> MgO + H2. What observation shows magnesium reacts? It glows and a white solid forms. Why should the first gas not be ignited immediately? It may be mixed with air and could explode. Practical connection: Label the steam-reaction apparatus and explain the sequence of heating. State why air should be displaced before testing the gas. Examination connection: The solid product is MgO, not Mg(OH)2, because magnesium reacts with steam.

Review questions and suggested answers