Non-metals, air and water

Air

About 78% nitrogen, 21% oxygen, 0.04% carbon dioxide, plus argon and water vapour. Pollutants: carbon monoxide (incomplete combustion, poisonous), sulfur dioxide (burning coal, acid rain), nitrogen oxides (car engines), particulates.

Water

Test: anhydrous copper(II) sulfate turns white to blue; cobalt chloride paper turns blue to pink. Purity: pure water boils at 100 °C and freezes at 0 °C. Water treatment: screening, sedimentation (with alum), filtration through sand, chlorination to kill bacteria.

Nitrogen and fertilisers

NPK fertilisers supply nitrogen, phosphorus and potassium. In Zimbabwe, Compound D (an NPK basal fertiliser) is applied at planting, and ammonium nitrate is used as a top dressing for extra nitrogen. Too much fertiliser washing into rivers causes eutrophication.

Sulfur

Used to make sulfuric acid (contact process) for fertilisers, batteries and detergents.

Carbon dioxide

Made by heating carbonates or acid on carbonates; used in fire extinguishers and fizzy drinks. A greenhouse gas: increasing levels contribute to global warming.

Gas tests

Hydrogen – squeaky pop; oxygen – relights glowing splint; CO₂ – lime water milky; ammonia – damp red litmus blue; chlorine – bleaches damp litmus.

Check yourself

1. What percentage of air is nitrogen?
2. Why is chlorine added to drinking water?
3. Name the gas that causes acid rain from burning coal.