AQA Chemistry 5.4.2.1–5.4.2.2
Reactions of acids with metals and bases
Every reaction makes a salt. What else it makes depends on what the acid meets. Pick an acid and a reactant, and predict before it runs.
Combined Science · Higher tier
Start here
A tablet in vinegar.
Drop an indigestion tablet into a glass of vinegar and watch it closely.
If you had to guess, does it give off a gas, or just quietly dissolve?
Predict, then run
What does the acid meet?
Acids produce hydrogen ions, H+, in water. Metal oxides and hydroxides are bases: they neutralise acids. An alkali is a base that dissolves in water. Choose an acid and a reactant, then predict the products.
Predict the products.
The four reactions
The salt comes from the metal and the acid.
Hydrochloric acid makes chlorides, sulfuric acid makes sulfates, nitric acid makes nitrates. The reactions with oxides, hydroxides and carbonates are all neutralisation. Only metals above hydrogen in the reactivity series react with dilute acids: copper doesn’t.
Formulae of salts
Balance the charges.
A salt has no overall charge. Take enough of each ion for the charges to cancel. Mg2+ needs two Cl−, so magnesium chloride is MgCl2. Two Na+ balance one SO42−, so sodium sulfate is Na2SO4. Now you.
Zinc chloride
Zn²⁺ and Cl⁻
Potassium sulfate
K⁺ and SO4²⁻
Calcium nitrate
Ca²⁺ and NO3⁻
Acid + metal is redox
The metal loses electrons; the hydrogen ions gain them.
Oxidation is loss of electrons; reduction is gain of electrons. In the ionic equation, the chloride or sulfate ions don’t change: they are spectator ions, so they are left out. Tap each half to see which species is oxidised and which is reduced.
Zinc and iron react the same way: Zn Zn2+ + 2e−; Fe Fe2+ + 2e−.
Think again · where does the fizz come from?
“Acid and a carbonate make a salt and water.”
Your call
ChooseCalcium carbonate is added to hydrochloric acid. Which list gives all the products?
Sort
Which products?
Place each reactant with what it makes with an acid.
Tap a card, then tap the box it belongs in. Tap a placed card to take it back.
Command words in this lesson
- Name
- The salt: metal first, then chloride, sulfate or nitrate.
- Write
- The formula, with charges balanced.
- Describe
- A test: what you do, and what you see.
Key fact
Acid + metal gives a salt and hydrogen. Acid + metal oxide or hydroxide gives a salt and water. Acid + carbonate gives a salt, water and carbon dioxide.
Key note · AQA 5.4.2.1–5.4.2.2
Reactions of acids
- Acids produce H⁺ ions in water. Bases (metal oxides and hydroxides) neutralise acids; alkalis are soluble bases.
- Acid + metal → salt + hydrogen (metals above hydrogen only; copper doesn’t react). Test: lit splint, squeaky pop.
- Acid + metal oxide or hydroxide → salt + water. Acid + carbonate → salt + water + carbon dioxide. Test: limewater milky. All three are neutralisation.
- Hydrochloric → chlorides; sulfuric → sulfates; nitric → nitrates.
- Salt formulae: balance the ion charges, e.g. Mg²⁺ + 2Cl⁻ → MgCl2.
- Higher: acid + metal is redox. The metal loses electrons (oxidised); H⁺ ions gain electrons (reduced).
Photograph this card. Tomorrow, cover it and say each line first.
Previous and next
Connects to
Ask MrBadmus
Not sure how to name the salt?
Reaction drawings are schematic. Making a pure, dry salt is the soluble-salts practical, in its own lesson.