5 · Neutralisation and acid reactions

Acid + alkali → salt + water

An acid and an alkali cancel each other out — neutralisation. Add just enough alkali to an acid and the pH lands on 7: neutral. Add too much, and it swings past neutral into alkaline.

hydrochloric acid + sodium hydroxide → sodium chloride + water

Acid + metal → salt + hydrogen

Some metals react with acids, fizzing as hydrogen gas is released and the metal dissolves. The confirmatory test: hold a lit splint at the mouth of the tube — a sharp squeaky pop means hydrogen.

dilute sulfuric acid + magnesium → magnesium sulfate + hydrogen

Acid + carbonate → salt + water + carbon dioxide

Carbonates fizz too, but the gas is different. The confirmatory test: bubble it through limewater — limewater turns cloudy when carbon dioxide passes through it.

dilute hydrochloric acid + calcium carbonate → calcium chloride + water + carbon dioxide

Naming the salt The salt's name comes from the metal (or alkali) plus the acid used: hydrochloric acid always makes a chloride, sulfuric acid always makes a sulfate, nitric acid always makes a nitrate.

Try it: run all three reactions

Pick a reaction type, then use the control below it.

Quick check

Q Dilute nitric acid is added to zinc carbonate. Write the word equation, and describe how you'd confirm the gas produced.

nitric acid + zinc carbonate → zinc nitrate + water + carbon dioxide

Bubble the gas through limewater — it turning cloudy confirms carbon dioxide.