Chemical changes · GCSE Chemistry
Neutralisation and salts
GCSE Chemistry revision on neutralisation and salts: acid plus metal, base or carbonate, naming chlorides, sulfates and nitrates, and writing equations with state symbols.
Metal → salt + hydrogen. Base → salt + water. Carbonate → salt + water + carbon dioxide. The salt name is metal plus chloride, sulfate or nitrate.
The important bits
What you need to know
- 1
Neutralisation: acid + base → salt + water. The ionic equation is H⁺(aq) + OH⁻(aq) → H₂O(l) when the base is an alkali.
- 2
Acid + metal → salt + hydrogen, for metals above hydrogen in the reactivity series: 2HCl(aq) + Mg(s) → MgCl₂(aq) + H₂(g). Test H₂ with a squeaky pop.
- 3
Acid + metal oxide or hydroxide → salt + water: H₂SO₄(aq) + CuO(s) → CuSO₄(aq) + H₂O(l). Copper does not make hydrogen with acid; use the oxide to make the salt.
- 4
Acid + carbonate → salt + water + carbon dioxide: 2HCl(aq) + CaCO₃(s) → CaCl₂(aq) + H₂O(l) + CO₂(g). Limewater turns cloudy.
- 5
Hydrochloric acid makes chlorides, sulfuric acid makes sulfates, nitric acid makes nitrates. Phosphoric acid (Triple) makes phosphates.
- 6
The metal (or ammonium) in the salt comes from the metal, base, alkali or carbonate. Sodium hydroxide plus nitric acid is sodium nitrate, NaNO₃.
- 7
Soluble salts from an insoluble base: add excess solid oxide/carbonate to the acid, filter off the leftover solid, evaporate to crystallise. From an alkali: use titration, then crystallise.
- 8
Ammonia is a soluble base: NH₃(aq) + HCl(aq) → NH₄Cl(aq). Ammonium chloride is the salt. Ammonium is NH₄⁺, not a metal ion.
Quotations worth analysing
Short evidence. Real method.
“acid + metal → salt + hydrogen”
Only for metals reactive enough to displace H⁺. Copper, silver and gold do not. State symbol for hydrogen is (g).
“acid + carbonate → salt + water + carbon dioxide”
CO₂(g) is the extra product. If you write only salt + water you have described a base, not a carbonate. Limewater is the test.
“H₂SO₄(aq) + 2NaOH(aq) → Na₂SO₄(aq) + 2H₂O(l)”
Sulfuric acid is diprotic: it can supply two H⁺. The salt is a sulfate, not a chloride. Balance the 2 in NaOH and in water.
Go deeper
Name the salt from the two halves of the reaction
The positive ion comes from the metal, base, alkali or carbonate. The negative ion comes from the acid: chloride, sulfate or nitrate. Magnesium plus hydrochloric acid is magnesium chloride, MgCl₂. Copper oxide plus sulfuric acid is copper sulfate, CuSO₄. Calcium carbonate plus nitric acid is calcium nitrate, Ca(NO₃)₂. If hydrogen is produced, a metal was used. If carbon dioxide is produced, a carbonate was used. If only salt and water appear, it was an oxide or hydroxide. That three-way split is how you choose the equation in a six-mark “describe how you would make a pure dry sample”.
Go deeper
Insoluble base method versus titration method
Copper sulfate from copper oxide: warm sulfuric acid, add CuO until some remains undissolved (acid used up), filter, evaporate the filtrate gently, leave to crystallise, pat dry. You cannot titrate copper oxide because it is an insoluble solid, not an alkali. Sodium sulfate from sodium hydroxide: do a titration with an indicator to find the exact volumes, then mix those volumes without indicator (or use the same volumes on a fresh pair) and crystallise. Indicator would contaminate the crystals. Excess alkali cannot be filtered out because it is dissolved. That is why the methods differ.
Go deeper
State symbols are free marks if you remember the tests
Metals are (s) unless already molten. Acids and alkalis in these reactions are (aq). Hydrogen and carbon dioxide are (g). Water is (l). Insoluble carbonates such as CaCO₃ and CuCO₃ are (s). Sodium carbonate is soluble, so Na₂CO₃(aq) is possible. Students write HCl(g) for hydrochloric acid, or H₂(aq) for hydrogen. If the question asks for the ionic equation of a carbonate with acid, include CO₃²⁻(s or aq) + 2H⁺(aq) → CO₂(g) + H₂O(l). Spectator metal ions can be left out when the command word wants ionic. Limewater turning cloudy is still the CO₂ test, not a state symbol.
See the idea in action
Make a pure dry sample of copper(II) sulfate crystals from copper(II) oxide. Warm dilute H₂SO₄(aq), add CuO(s) until excess remains, filter off unreacted CuO, evaporate the blue CuSO₄(aq) to a small volume, leave to crystallise, then dry the crystals between filter papers. Equation: CuO(s) + H₂SO₄(aq) → CuSO₄(aq) + H₂O(l). You would not use copper metal: copper is below hydrogen and does not produce H₂ with the acid.
Exam technique
Turn knowledge into marks
Learn the three construction reactions until they are automatic, then name the salt from the acid. In a method question, say excess insoluble solid, filter, crystallise — or titration if both reagents are solutions. Include state symbols.
Common mistakes
Do not give these marks away
- 01
Naming sodium chloride from sulfuric acid, or forgetting CO₂ from a carbonate.
- 02
Trying to make a copper salt by adding copper metal to acid.
- 03
Leaving indicator in the salt you crystallise after a titration.
What are the products when hydrochloric acid reacts with calcium carbonate?
ACalcium chloride and hydrogen
BCalcium chloride, water and carbon dioxide
CCalcium sulfate and water
DCalcium hydroxide and carbon dioxide
Show the answer
Calcium chloride, water and carbon dioxide. Acid plus carbonate always gives a salt, water and carbon dioxide. Hydrochloric acid produces a chloride, so the salt is calcium chloride.
Quick questions
If this is the bit you searched
How do you name a salt from a neutralisation GCSE Chemistry?
Take the metal or ammonium from the base, alkali or carbonate, and the ending from the acid: hydrochloric → chloride, sulfuric → sulfate, nitric → nitrate.
What is the difference between a base and an alkali?
A base is a metal oxide or hydroxide that neutralises an acid. An alkali is a soluble base, so it produces OH⁻(aq) in water.
How do you make copper sulfate crystals from copper oxide?
Add excess copper oxide to warm sulfuric acid, filter, evaporate the filtrate and leave it to crystallise. Equation: CuO + H₂SO₄ → CuSO₄ + H₂O.
What gas is produced when an acid reacts with a metal?
Hydrogen, H₂(g), if the metal is above hydrogen in the reactivity series. Test with a lighted splint: squeaky pop.