What an oxide tells

Graphite shines and conducts, like a metal. Yet it is a non-metal. A chemical test on its oxide helps to show why.

The rule

An oxide is a compound of an element with oxygen. A basic oxide reacts with an acid. An acidic oxide reacts with a base. Metal oxides are usually basic. Some, like aluminium oxide, act both ways. Non-metal oxides are usually acidic. Some, like carbon monoxide, are neutral. An acidic oxide is a sign of a non-metal.

Worked example

Graphite is a form of carbon. It burns to carbon dioxide. Carbon dioxide reacts with a base. That oxide is acidic, which fits a non-metal. Graphite is a non-metal, even though it conducts.

Aluminium oxide reacts with both acids and bases. So it is amphoteric. Zinc oxide is amphoteric too.