Properties of the combustion products
Carbon dioxide is colourless and odourless. It does not burn and does not help things burn, it is heavier than air, and it dissolves in water to form carbonic acid. It is the product of complete combustion and a greenhouse gas, but it is not a poison like carbon monoxide. Carbon monoxide is colourless, odourless and toxic. Water vapour condenses to droplets on cooling. Soot is a fine black solid, carbon. Sulphur dioxide comes from sulphur in some fuels. It is colourless, has a choking smell and dissolves in water to give sulphurous acid. Nitrogen oxides form when a fuel burns at high temperature in air: the nitrogen and the oxygen of the air combine. Nitric oxide is colourless and turns in air into nitrogen dioxide, which is reddish-brown with a choking smell; it makes nitrous and nitric acids in water. The acids from sulphur dioxide and nitrogen oxides make acid rain, which can harm plants, water life and stone buildings.
| Product | Colour and smell | Note |
|---|---|---|
| CO₂ | none, none | not toxic; makes carbonic acid in water |
| CO | none, none | toxic |
| SO₂ | none; choking smell | makes sulphurous acid |
| NO₂ | reddish-brown; choking smell | makes nitric and nitrous acids |
Property cards. Write the six products (CO₂, CO, water vapour, soot, SO₂, nitrogen oxides) on cards and the properties on other cards: colourless gas and toxic; fine black solid; choking smell; reddish-brown gas; condenses on cooling; does not burn and is heavier than air. Match each product to its properties with a partner. Say which ones lead to acid rain. No smelling or testing of real gases is needed.