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Physical properties of hydrogen

• colourless, odourless gas
• insoluble in water
• less dense than air
• hydrogen is diatomic, H₂

Preparing and collecting hydrogen gas

We prepare hydrogen by reacting zinc or magnesium with dilute hydrochloric acid:

Zn + 2HCl → ZnCl₂ + H₂

Mg + 2HCl → MgCl₂ + H₂

• hydrogen is insoluble in water, so can collect it using a gas jar in a trough of water.
• dilute hydrochloric acid reacts vigorously with magnesium and can be dangerous.

Test for hydrogen

A lit splint applied to hydrogen gas will result in a popping sound.

Hydrogen uses

• making the fats in margarines solidify
• weather balloons
• an alternative to hydrocarbon fuels