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Every sample of water ever split has given exactly twice the volume of hydrogen. Follow what that forces you to conclude about atoms, in an interactive playground.

Reactions happen in ratios of particles, and particles cannot be counted. The mole is how chemistry counts by weighing instead. Match three equal-sized samples to their masses in an interactive playground.

A relative formula mass is four steps of arithmetic, and almost every mistake is made in the first one. Work through a formula with brackets in an interactive playground.

A balanced equation tells you a ratio of particles, and a balance reads grams. Converting between them is the whole calculation. Follow it step by step in an interactive playground.

A mass calculation gives the theoretical maximum, and real reactions always fall short. Three separate reasons, only one of which is carelessness. Trace them in an interactive playground.

The reactivity series is usually handed over as a list to memorise. It is actually the result of three simple tests, and the order falls out of them. Build it step by step in an interactive playground.

Put zinc into copper sulfate and the blue fades. Put copper into zinc sulfate and nothing at all happens. One rule predicts which way round it works, in an interactive playground.

Gold is dug up as metal and aluminium never is, though aluminium is far more common. Reactivity explains both, and the order metals were discovered in. Trace it in an interactive playground.

There are three ways to get a metal out of the ground, and which one you need is decided entirely by where the metal sits relative to carbon. Sort them in an interactive playground.

Aluminium sits well above iron in the reactivity series, so it ought to corrode faster. It does, and then stops. The reason is physical rather than chemical. Follow it in an interactive playground.

Petrol vapour and air sit together for years without reacting, then go off in milliseconds. Work out what was missing, and what a reaction rate counts, in an interactive playground.

Temperature, concentration, surface area and catalysts look like four unrelated tricks. They are two, and knowing which is which tells you what each one will do. Sort them in an interactive playground.

Two curves, one reaction, two speeds. The steepness tells you the rate and the final height tells you the amount — and they are different things. Label both curves in an interactive playground.

A catalyst speeds a reaction up without being used up and without adding any energy. Work out how that is possible, in an interactive playground.

A lump of flour burns slowly and a cloud of it explodes. Same substance, same mass, and the only difference is how much of it the air can reach. Trace the consequences in an interactive playground.

Boiling a kettle looks violent and changes nothing; a nail rusting looks like nothing and changes everything. One test separates them. Follow both routes in an interactive playground.

Burning looks like matter disappearing and rusting looks like matter appearing. Neither happens. Follow the reasoning to conservation of mass in an interactive playground.

A chemical equation is a sentence with a fixed grammar. Label every part of one — including the two numbers that look alike and mean completely different things — in an interactive playground.

Balancing is not algebra and has nothing to do with doing the same to both sides. It is a count of atoms, and only one of the two numbers may be touched. Follow the reasoning in an interactive playground.

Every reaction breaks bonds and makes bonds, and which total is larger decides whether the surroundings warm or cool. Follow both outcomes from one starting point in an interactive playground.