Why is "Writing acid + carbonate → salt + carbon dioxide and forgetting the water" a common mistake in Reactions to acids with metals?

Why it happens: Students see the fizzing (CO₂) and stop, overlooking the second invisible product. How to avoid it: Memorise the full pattern: acid + carbonate → **salt + water + carbon dioxide** — three products every time. Source: Edexcel Chemistry examiner reports — recurring error

Why is "Giving a vague gas test such as 'it pops' or 'it changes colour'" a common mistake in Reactions to acids with metals?

Why it happens: Students remember roughly what happens but not the precise test or wording. How to avoid it: Be exact: hydrogen = **lit splint → squeaky pop**; carbon dioxide = **limewater → turns milky**. State both the test AND the result. Source: Edexcel Chemistry examiner reports

Why is "Writing hydrogen as H instead of H₂" a common mistake in Reactions to acids with metals?

Why it happens: Students forget that hydrogen gas is a diatomic molecule. How to avoid it: Hydrogen gas is always **H₂**. Equations like Mg + 2HCl → MgCl₂ + H₂ only balance with H₂, not H. Source: Edexcel Chemistry examiner reports

Why is "Getting the salt formula wrong, e.g. writing MgCl or ZnCl instead of MgCl₂ / ZnCl₂" a common mistake in Reactions to acids with metals?

Why it happens: Students ignore ion charges when combining the metal with the anion. How to avoid it: Balance the charges: Mg²⁺ and Zn²⁺ need **two** Cl⁻ ions → MgCl₂, ZnCl₂. Then balance the whole equation. Source: Edexcel Chemistry examiner reports

Why is "Saying copper (or silver/gold) reacts with dilute acid to give hydrogen" a common mistake in Reactions to acids with metals?

Why it happens: Students apply 'acid + metal → salt + hydrogen' to every metal. How to avoid it: Only metals **above hydrogen** in the reactivity series react. Copper, silver and gold do **not** react — there is no fizzing. Source: Edexcel Chemistry examiner reports

Why is "Writing 'sulphate' or confusing nitrate with nitrite" a common mistake in Reactions to acids with metals?

Why it happens: Old spellings and similar-sounding ions cause slips. How to avoid it: Use the modern spelling **sulfate**, and the **nitrate** (NO₃⁻) ending from nitric acid — 'nitrite' (NO₂⁻) is a different ion. Source: Edexcel Chemistry examiner reports

Edexcel IGCSE Science(Double Award)-Chemistry (4WSD0-1C)

Reactions to acids with metals

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Detailed Study Notes

Detailed notes on Acids, bases and salt preparations for Edexcel IGCSE Science(Double Award)-Chemistry, covering key concepts, explanations, examples, and exam-focused revision points.

Reactions of Acids with Metals — Edexcel International GCSE Science (Double Award) Chemistry (4WSD0-1C) Study Notes

The three general reactions of acids — with metals, with bases and with carbonates — and how to name the salt formed from hydrochloric, sulfuric and nitric acids. Includes word and balanced symbol equations with state symbols, plus the gas tests (squeaky pop for hydrogen, limewater turning milky for carbon dioxide). Covers Double Award Chemistry spec 2.40–2.41, assessed on Chemistry Paper 1 (4WSD0/1C).

At a glance

Acid + metal → salt + hydrogen (e.g. Mg + H₂SO₄ → MgSO₄ + H₂). Only metals above hydrogen react.
Acid + base (metal oxide/hydroxide) → salt + water — this is neutralisation.
Acid + metal carbonate → salt + water + carbon dioxide.
Salt naming follows the acid: hydrochloric → chloride, sulfuric → sulfate, nitric → nitrate.
Hydrogen test: a lit splint gives a squeaky pop.
Carbon dioxide test: the gas turns limewater milky (cloudy white).
Always balance symbol equations and add state symbols (s), (l), (g), (aq).

What you’ll learn

Mapped to the Edexcel IGCSE 4WSD0-1C syllabus (2026 onwards).

2.40 — Recall the general reactions of acids with metals, bases and carbonates.
2.41 — Name salts produced from hydrochloric, sulfuric and nitric acids (chlorides, sulfates, nitrates).

Acid + metal → salt + hydrogen (spec 2.40)

A reactive metal displaces hydrogen from an acid, giving a salt and hydrogen gas.

When a reactive metal is added to a dilute acid, the metal dissolves, the mixture fizzes, and hydrogen gas is given off. The general pattern is:

acid + metal → salt + hydrogen

Only metals above hydrogen in the reactivity series react this way (for example magnesium, zinc, iron). Unreactive metals such as copper, silver and gold do not react with dilute acids — there is no fizzing.

Hydrogen given off by the metal gives a squeaky pop with a lit splint.

Worked examples of the pattern:

Acid	Metal	Balanced equation
Sulfuric acid	Magnesium	Mg + H₂SO₄ → MgSO₄ + H₂
Hydrochloric acid	Magnesium	Mg + 2HCl → MgCl₂ + H₂
Hydrochloric acid	Zinc	Zn + 2HCl → ZnCl₂ + H₂
Sulfuric acid	Iron	Fe + H₂SO₄ → FeSO₄ + H₂

Observations to quote in the exam:

The metal gradually dissolves / gets smaller.
Bubbles of gas (fizzing) are produced.
The mixture gets warmer (the reaction is exothermic).

Testing the gas — hydrogen. Hold a lit (burning) splint at the mouth of the tube. Hydrogen burns with a squeaky "pop". That squeaky pop is the mark-scheme answer — "it pops" or "it goes out" alone will not score.

acid + metal → salt + hydrogen.
Only metals above hydrogen react (Cu, Ag, Au do not).
Observations: metal dissolves, fizzing, mixture warms up.
Hydrogen test: lit splint → squeaky pop.

See the full worked example for reactions to acids with metals →

Acid + base → salt + water (spec 2.40)

A base (metal oxide or hydroxide) neutralises an acid to give a salt and water only.

A base is a substance that neutralises an acid. Bases include metal oxides (such as CuO, MgO) and metal hydroxides (such as NaOH, KOH). The general pattern is:

acid + base → salt + water

This is called neutralisation. There is no gas given off — just a salt dissolved in water.

Acid	Base	Balanced equation
Sulfuric acid	Copper(II) oxide	CuO + H₂SO₄ → CuSO₄ + H₂O
Hydrochloric acid	Sodium hydroxide	HCl + NaOH → NaCl + H₂O
Nitric acid	Potassium hydroxide	HNO₃ + KOH → KNO₃ + H₂O
Hydrochloric acid	Magnesium oxide	MgO + 2HCl → MgCl₂ + H₂O

Observations: with a solid base (e.g. black CuO + sulfuric acid), the solid dissolves as it is added and the solution turns blue (copper(II) sulfate). No fizzing — that tells you it is a base, not a carbonate.

The key idea behind every neutralisation is the hydrogen ion reacting with the hydroxide ion to make water:

H⁺(aq) + OH⁻(aq) → H₂O(l)

acid + base → salt + water (neutralisation).
Bases = metal oxides (CuO, MgO) and hydroxides (NaOH, KOH).
No gas is given off — distinguishes a base from a carbonate.
Core reaction: H⁺ + OH⁻ → H₂O.

See the full worked example for reactions to acids with metals →

Acid + carbonate → salt + water + carbon dioxide (spec 2.40)

Carbonates fizz with acids, giving carbon dioxide that turns limewater milky.

When an acid is added to a metal carbonate, it fizzes vigorously and releases carbon dioxide gas. The general pattern is:

acid + metal carbonate → salt + water + carbon dioxide

This reaction always gives three products — students often forget the water.

Acid	Carbonate	Balanced equation
Hydrochloric acid	Calcium carbonate	CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂
Sulfuric acid	Sodium carbonate	Na₂CO₃ + H₂SO₄ → Na₂SO₄ + H₂O + CO₂
Nitric acid	Calcium carbonate	CaCO₃ + 2HNO₃ → Ca(NO₃)₂ + H₂O + CO₂

Carbon dioxide turns limewater milky (cloudy white) — the classic gas test.

Testing the gas — carbon dioxide. Bubble the gas through limewater (calcium hydroxide solution). Carbon dioxide turns the limewater milky / cloudy white. "It goes white" is acceptable; "it changes colour" is not specific enough.

Spot the difference: a carbonate fizzes and the gas turns limewater milky (CO₂); a metal fizzes and the gas gives a squeaky pop (H₂). The two fizzing reactions are told apart by the gas test.

acid + carbonate → salt + water + carbon dioxide (three products).
Don't forget the water!
CO₂ test: bubble through limewater → turns milky/cloudy white.
Fizz + milky limewater = CO₂ (carbonate); fizz + pop = H₂ (metal).

See the full worked example for reactions to acids with metals →

Naming the salt (spec 2.41)

The metal gives the first part of the salt name; the acid gives the ending.

Every salt name has two parts: the metal (from the metal, oxide, hydroxide or carbonate) comes first, and the ending comes from the acid used.

The acid decides the ending of the salt name; the metal goes in front.

Acid used	Salt ending	Examples
Hydrochloric acid (HCl)	chloride	NaCl, MgCl₂, ZnCl₂
Sulfuric acid (H₂SO₄)	sulfate	CuSO₄, MgSO₄, ZnSO₄
Nitric acid (HNO₃)	nitrate	KNO₃, NaNO₃, Ca(NO₃)₂
(Phosphoric acid, H₃PO₄)	phosphate	Na₃PO₄

How to build a salt name in two steps:

Metal comes first — copper, magnesium, sodium, etc.
Ending comes from the acid — chloride / sulfate / nitrate.

So zinc + sulfuric acid → zinc sulfate; magnesium + hydrochloric acid → magnesium chloride; copper(II) oxide + nitric acid → copper(II) nitrate.

Spelling matters: the examiner wants sulfate (not "sulphate"), and nitrate (not "nitrite"). A nitrite is a different ion — losing the mark for the wrong ending is avoidable.

Salt name = metal + ending from the acid.
HCl → chloride; H₂SO₄ → sulfate; HNO₃ → nitrate.
e.g. zinc + sulfuric acid → zinc sulfate.
Watch spelling: sulfate (not sulphate); nitrate (not nitrite).

See the full worked example for reactions to acids with metals →

Writing word and balanced symbol equations

Predict products from the pattern, then balance the symbol equation and add state symbols.

Most marks in this topic come from writing equations correctly. Work through this routine every time:

Decide which pattern you are using (metal, base or carbonate) → write the word equation.
Write the formulae of every reactant and product (get the charges right so formulae like CaCl₂ and MgSO₄ are correct).
Balance the symbol equation — adjust the numbers in front only, never the small subscripts.
Add state symbols: (s) solid, (l) liquid, (g) gas, (aq) dissolved in water.

Worked routine — magnesium + hydrochloric acid:

Word: magnesium + hydrochloric acid → magnesium chloride + hydrogen
Formulae: Mg + HCl → MgCl₂ + H₂
Balance (2 HCl needed for 2 Cl): Mg + 2HCl → MgCl₂ + H₂
State symbols: Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g)

Why balancing matters: atoms are never created or destroyed, so the number of each type of atom must be the same on both sides. In Mg + 2HCl → MgCl₂ + H₂ there are 2 H and 2 Cl on each side — balanced.

A safe order of attack: balance the metal first, then the non-metal from the acid (Cl, the SO₄ group or the NO₃ group), and finally check the hydrogen.

Word equation first, then formulae, then balance, then state symbols.
Balance by changing big numbers in front, never small subscripts.
State symbols: (s) (l) (g) (aq).
Same number of each atom on both sides = balanced.

See the full worked example for reactions to acids with metals →

Quick recap

acid + metal → salt + hydrogen (only metals above hydrogen react; Cu/Ag/Au do not).
acid + base → salt + water (neutralisation; no gas).
acid + carbonate → salt + water + carbon dioxide (don't forget the water).
Salt naming: HCl → chloride, H₂SO₄ → sulfate, HNO₃ → nitrate; metal goes first.
Gas tests: hydrogen = squeaky pop with a lit splint; carbon dioxide = turns limewater milky.

Memorise this

Verbatim phrases and definitions Edexcel mark schemes credit.

acid + metal → salt + hydrogen (Mg + H₂SO₄ → MgSO₄ + H₂).
acid + base → salt + water; acid + carbonate → salt + water + CO₂.
HCl → chloride; H₂SO₄ → sulfate; HNO₃ → nitrate.
Hydrogen test = squeaky pop; carbon dioxide test = limewater turns milky.
Always balance the symbol equation and add state symbols (s)(l)(g)(aq).

How it’s examined

Double Award Chemistry is assessed on one untiered paper — Chemistry Paper 1 (4WSD0/1C), 2 hours, 110 marks, 33.3% of the Double Award (calculator allowed). The reactions of acids appear almost every series: complete the word equation for an acid reacting with a metal/base/carbonate (1–2 marks); name the salt formed by a given acid (1 mark — pure recall of the chloride/sulfate/nitrate rule); write and balance the symbol equation with state symbols (2–3 marks); and identify the gas from an observation using the correct test (squeaky pop / limewater milky). The biggest mark-droppers are forgetting the water in the carbonate reaction and giving a vague gas test.

Sources: Pearson Edexcel International GCSE Science (Double Award) 4SD0 specification — Issue 4 (valid for 2026 onwards); Pearson Edexcel International GCSE Chemistry 4CH1 specification — Issue 4 (shared Chemistry Paper 1 content); Pearson Edexcel 4SD0 / 4CH1 examiner reports 2022–2024. Last reviewed 2026-06-07.

Take this whole topic with you

Step-by-step worked examples — Reactions to acids with metals

Step-by-step solutions to past-paper-style questions on reactions to acids with metals, written exactly the way a tutor would explain them at the board.

Question type:

1Name the salt formed (Getting started)
Getting startedIdentify & classify• 4WSD0/1C style — short answer• salt-naming, spec-2.41
Question
Name the salt formed when: (a) magnesium reacts with hydrochloric acid; (b) zinc reacts with sulfuric acid; (c) potassium hydroxide reacts with nitric acid. (3 marks)
Step-by-step solution
1. Step 1
  (a) The metal is magnesium; hydrochloric acid gives a chloride → magnesium chloride.
2. Step 2
  (b) The metal is zinc; sulfuric acid gives a sulfate → zinc sulfate.
3. Step 3
  (c) The metal is potassium; nitric acid gives a nitrate → potassium nitrate.
Answer
(a) magnesium chloride; (b) zinc sulfate; (c) potassium nitrate.
Examiner tip
Salt name = metal first, then the ending from the acid. HCl → chloride, H₂SO₄ → sulfate, HNO₃ → nitrate. Spelling 'sulfate' (not sulphate) and 'nitrate' (not nitrite) is expected.
2Complete the general word equations (Getting started)
Getting startedIdentify & classify• 4WSD0/1C style — short answer• general-reactions, spec-2.40
Question
Complete each word equation: (a) acid + metal → ___ + ___; (b) acid + base → ___ + ___; (c) acid + metal carbonate → ___ + ___ + ___. (3 marks)
Step-by-step solution
1. Step 1
  (a) acid + metal → salt + hydrogen.
2. Step 2
  (b) acid + base → salt + water (neutralisation).
3. Step 3
  (c) acid + metal carbonate → salt + water + carbon dioxide — three products.
Answer
(a) salt + hydrogen; (b) salt + water; (c) salt + water + carbon dioxide.
Examiner tip
All three patterns must be memorised. The most commonly lost mark is forgetting the WATER in the carbonate reaction — it has three products, not two.
3Balance an acid + metal equation (Building confidence)
Building confidenceMulti-step problem• 4WSD0/1C style — structured• equations, acid-metal, spec-2.40
Question
Zinc reacts with dilute hydrochloric acid. Write a balanced symbol equation, including state symbols, for the reaction. (3 marks)
Step-by-step solution
1. Step 1
  Predict products. acid + metal → salt + hydrogen. The salt is zinc chloride (ZnCl₂).
2. Step 2
  Unbalanced formulae. Zn + HCl → ZnCl₂ + H₂. There are 2 Cl and 2 H on the right but only 1 of each on the left.
3. Step 3
  Balance. Put a 2 in front of HCl: Zn + 2HCl → ZnCl₂ + H₂. Now 2 H and 2 Cl on each side.
4. Step 4
  Add state symbols: Zn(s) + 2HCl(aq) → ZnCl₂(aq) + H₂(g).
Answer
Zn(s) + 2HCl(aq) → ZnCl₂(aq) + H₂(g).
Examiner tip
Marks: correct products + balancing + state symbols. Zinc chloride is ZnCl₂ (Zn²⁺ needs two Cl⁻), so 2HCl is required. Hydrogen is H₂, never H.
4Acid + base, name salt and balance (Building confidence)
Building confidenceMulti-step problem• 4WSD0/1C style — structured• equations, neutralisation, spec-2.40, spec-2.41
Question
Copper(II) oxide reacts with dilute sulfuric acid. (a) Name the salt formed. (b) Write a balanced symbol equation. (c) State one observation. (3 marks)
Step-by-step solution
1. Step 1
  (a) acid + base → salt + water. Sulfuric acid → a sulfate; the metal is copper → copper(II) sulfate.
2. Step 2
  (b) Formulae: CuO + H₂SO₄ → CuSO₄ + H₂O. Check atoms: 1 Cu, 1 S, 5 O, 2 H on each side — already balanced.
3. Step 3
  (c) Observation: the black copper(II) oxide dissolves and the solution turns blue (copper(II) sulfate).
Answer
(a) copper(II) sulfate; (b) CuO + H₂SO₄ → CuSO₄ + H₂O; (c) the black solid dissolves and the solution turns blue.
Examiner tip
No gas is produced in acid + base, which distinguishes it from acid + carbonate. The blue colour of the copper(II) salt is a reliable observation mark.
5Acid + carbonate with the gas test (Stretch)
StretchMulti-step problem• 4WSD0/1C style — extended• equations, carbonate, gas-test, spec-2.40
Question
Calcium carbonate is added to dilute hydrochloric acid. (a) Write a balanced symbol equation with state symbols. (b) Describe a test, and the result, to identify the gas produced. (4 marks)
Step-by-step solution
1. Step 1
  Products. acid + carbonate → salt + water + carbon dioxide. Salt = calcium chloride (CaCl₂).
2. Step 2
  Unbalanced: CaCO₃ + HCl → CaCl₂ + H₂O + CO₂. The right has 2 Cl but the left has 1 — put a 2 in front of HCl.
3. Step 3
  Balanced + states: CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g).
4. Step 4
  Gas test (b). Bubble the gas through limewater; it turns milky / cloudy white, confirming carbon dioxide.
Answer
(a) CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g). (b) Bubble the gas through limewater — it turns milky (cloudy white), showing the gas is carbon dioxide.
Examiner tip
Full marks need three products (don't drop the water), correct balancing/state symbols, and the named test (limewater) WITH the result (turns milky). 'It changes colour' is too vague.
6Predict, name and balance for an unfamiliar acid (Stretch)
StretchMulti-step problem• 4WSD0/1C style — extended• equations, prediction, spec-2.40, spec-2.41
Question
Sodium carbonate (Na₂CO₃) reacts with dilute nitric acid. (a) Name the salt. (b) Predict the products and write a balanced symbol equation. (c) Name the gas and state how you would test for it. (4 marks)
Step-by-step solution
1. Step 1
  (a) Nitric acid → a nitrate; the metal is sodium → sodium nitrate (NaNO₃).
2. Step 2
  (b) Pattern. acid + carbonate → salt + water + carbon dioxide. Formulae: Na₂CO₃ + HNO₃ → NaNO₃ + H₂O + CO₂.
3. Step 3
  Balance. Na₂CO₃ has 2 Na, so 2 NaNO₃ are needed, which needs 2 HNO₃: Na₂CO₃ + 2HNO₃ → 2NaNO₃ + H₂O + CO₂.
4. Step 4
  (c) The gas is carbon dioxide; test by bubbling through limewater, which turns milky.
Answer
(a) sodium nitrate; (b) Na₂CO₃ + 2HNO₃ → 2NaNO₃ + H₂O + CO₂; (c) carbon dioxide — turns limewater milky.
Examiner tip
The 1:2 carbonate-to-acid ratio (because Na₂CO₃ has two Na) catches students out. Balance the metal first, then the nitrate group, then check H and O.

Model Answers — Reactions to acids with metals

High-scoring sample answers for reactions to acids with metals on the Pearson Edexcel IGCSE Chemistry Paper 1 (4WSD0/1C) paper, with examiner-style notes mapping each response to the mark scheme and assessment objectives.

Question 1
4WSD0/1C style2 marks
Complete the general equations for the reactions of acids: (a) acid + metal → ___; (b) acid + metal carbonate → ___. (2 marks)
Model answer
(a) acid + metal → salt + hydrogen.

(b) acid + metal carbonate → salt + water + carbon dioxide.
Why this scores
1 mark each. In (b), all three products are needed for the mark — omitting the water is the single most common error here.
Question 2
4WSD0/1C style3 marks
State the salt ending produced by each acid, and give one example salt: (a) hydrochloric acid; (b) sulfuric acid; (c) nitric acid. (3 marks)
Model answer
(a) Hydrochloric acid → chloride (e.g. sodium chloride, NaCl).

(b) Sulfuric acid → sulfate (e.g. magnesium sulfate, MgSO₄).

(c) Nitric acid → nitrate (e.g. potassium nitrate, KNO₃).
Why this scores
1 mark each. The ending alone scores the mark; the example confirms understanding. Use 'sulfate', not 'sulphate'.
Question 3
4WSD0/1C style4 marks
A piece of magnesium is added to dilute sulfuric acid. (a) Write a balanced symbol equation with state symbols. (b) Give two observations. (c) Describe a test to confirm the gas produced. (4 marks)
Model answer
(a) Mg(s) + H₂SO₄(aq) → MgSO₄(aq) + H₂(g).

(b) Any two of: the magnesium fizzes / gives off bubbles of gas; the magnesium gradually dissolves / gets smaller; the mixture gets warmer (exothermic).

(c) Hold a lit (burning) splint at the mouth of the tube — the gas (hydrogen) burns with a squeaky pop.
Why this scores
Marks: correct balanced equation + state symbols (1), two observations (2), the squeaky-pop test (1). The equation is already balanced 1:1 — but H₂ must be written as a molecule.
Question 4
4WSD0/1C style4 marks
Two unlabelled white solids are a metal and a metal carbonate. Both fizz when dilute hydrochloric acid is added. Explain how you could use the gas given off to tell which solid is which. (4 marks)
Model answer
A metal reacts with acid to give hydrogen; a carbonate gives carbon dioxide, so the gas tells them apart.

Collect the gas from each and test it.

For the gas that gives a squeaky pop with a lit splint, the solid is the metal (hydrogen).

For the gas that turns limewater milky (cloudy white), the solid is the metal carbonate (carbon dioxide).
Why this scores
The key is matching the correct test to the correct gas: pop = hydrogen = metal; limewater milky = carbon dioxide = carbonate. Vague answers ('test the gas') without the result score nothing.
Question 5
4WSD0/1C style — extended8 marks
Dilute hydrochloric acid is reacted separately with: (i) zinc, (ii) sodium hydroxide, and (iii) calcium carbonate. For each, write a balanced symbol equation (with state symbols) and name the salt formed. (8 marks)
Model answer
(i) Zinc (acid + metal → salt + hydrogen).

Equation: Zn(s) + 2HCl(aq) → ZnCl₂(aq) + H₂(g). (1)

Salt: zinc chloride. (1)

(ii) Sodium hydroxide (acid + base → salt + water).

Equation: HCl(aq) + NaOH(aq) → NaCl(aq) + H₂O(l). (1)

Salt: sodium chloride. (1)

(iii) Calcium carbonate (acid + carbonate → salt + water + carbon dioxide).

Equation: CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g). (1)

Salt: calcium chloride. (1)

All three salts are chlorides because the acid is hydrochloric acid. (2 — for correct balancing/state symbols across the three equations.)
Why this scores
Each equation must be correctly balanced with state symbols. Note 2HCl is needed in (i) and (iii) but only 1 in (ii). The carbonate equation has three products — dropping the water loses a mark.
Question 6
4WSD0/1C style — extended6 marks
Iron reacts with dilute sulfuric acid, and separately magnesium carbonate (MgCO₃) reacts with dilute nitric acid. For each reaction, name the salt, write a balanced symbol equation with state symbols, and (for any gas) state the test and result. (6 marks)
Model answer
Iron + sulfuric acid (acid + metal → salt + hydrogen).

Salt: iron(II) sulfate. (1)

Equation: Fe(s) + H₂SO₄(aq) → FeSO₄(aq) + H₂(g). (1)

Gas test: lit splint → squeaky pop (hydrogen). (1)

Magnesium carbonate + nitric acid (acid + carbonate → salt + water + CO₂).

Salt: magnesium nitrate. (1)

Equation: MgCO₃(s) + 2HNO₃(aq) → Mg(NO₃)₂(aq) + H₂O(l) + CO₂(g). (1)

Gas test: bubble through limewater → turns milky (carbon dioxide). (1)
Why this scores
Magnesium nitrate is Mg(NO₃)₂ (Mg²⁺ needs two NO₃⁻), which requires 2HNO₃. Match the gas test to the gas: pop for hydrogen, limewater milky for carbon dioxide.

Key Definitions and Keywords — Reactions to acids with metals

Definitions to memorise and the exact keywords mark schemes credit for reactions to acids with metals answers — sharpened from recent examiner reports for the 2026 Pearson Edexcel IGCSE Chemistry Paper 1 (4WSD0/1C) sitting.

Acid
Examiner keyword
A substance that produces hydrogen ions (H⁺) when dissolved in water; reacts with metals, bases and carbonates.
Base
Examiner keyword
A substance that neutralises an acid, including metal oxides and metal hydroxides; reacts with an acid to give a salt and water.
Salt
Examiner keyword
The compound formed when the hydrogen of an acid is replaced by a metal (or ammonium) ion, e.g. magnesium sulfate or sodium chloride.
Neutralisation
Examiner keyword
The reaction of an acid with a base to form a salt and water only: H⁺ + OH⁻ → H₂O.
Metal carbonate
Examiner keyword
A compound containing the carbonate ion (CO₃²⁻); reacts with acids to give a salt, water and carbon dioxide.
Chloride
Examiner keyword
The salt produced by hydrochloric acid (HCl), e.g. sodium chloride NaCl.
Sulfate
Examiner keyword
The salt produced by sulfuric acid (H₂SO₄), e.g. copper(II) sulfate CuSO₄.
Nitrate
Examiner keyword
The salt produced by nitric acid (HNO₃), e.g. potassium nitrate KNO₃.
Test for hydrogen
A lit (burning) splint held near the gas gives a squeaky 'pop'.
Test for carbon dioxide
Bubbling the gas through limewater (calcium hydroxide solution) turns it milky (cloudy white).

Common Mistakes and Misconceptions — Reactions to acids with metals

The traps other students keep falling into on reactions to acids with metals questions — taken from recent Pearson Edexcel IGCSE Chemistry Paper 1 (4WSD0/1C) examiner reports and mark schemes — and how to avoid them.

✕Writing acid + carbonate → salt + carbon dioxide and forgetting the water
Edexcel Chemistry examiner reports — recurring error
Why it happens
Students see the fizzing (CO₂) and stop, overlooking the second invisible product.
How to avoid it
Memorise the full pattern: acid + carbonate → salt + water + carbon dioxide — three products every time.
✕Giving a vague gas test such as 'it pops' or 'it changes colour'
Edexcel Chemistry examiner reports
Why it happens
Students remember roughly what happens but not the precise test or wording.
How to avoid it
Be exact: hydrogen = lit splint → squeaky pop; carbon dioxide = limewater → turns milky. State both the test AND the result.
✕Writing hydrogen as H instead of H₂
Edexcel Chemistry examiner reports
Why it happens
Students forget that hydrogen gas is a diatomic molecule.
How to avoid it
Hydrogen gas is always H₂. Equations like Mg + 2HCl → MgCl₂ + H₂ only balance with H₂, not H.
✕Getting the salt formula wrong, e.g. writing MgCl or ZnCl instead of MgCl₂ / ZnCl₂
Edexcel Chemistry examiner reports
Why it happens
Students ignore ion charges when combining the metal with the anion.
How to avoid it
Balance the charges: Mg²⁺ and Zn²⁺ need two Cl⁻ ions → MgCl₂, ZnCl₂. Then balance the whole equation.
✕Saying copper (or silver/gold) reacts with dilute acid to give hydrogen
Edexcel Chemistry examiner reports
Why it happens
Students apply 'acid + metal → salt + hydrogen' to every metal.
How to avoid it
Only metals above hydrogen in the reactivity series react. Copper, silver and gold do not react — there is no fizzing.
✕Writing 'sulphate' or confusing nitrate with nitrite
Edexcel Chemistry examiner reports
Why it happens
Old spellings and similar-sounding ions cause slips.
How to avoid it
Use the modern spelling sulfate, and the nitrate (NO₃⁻) ending from nitric acid — 'nitrite' (NO₂⁻) is a different ion.

Reactions to acids with metals

Detailed Study Notes

At a glance

What you’ll learn

Quick recap

Memorise this

How it’s examined

Take this whole topic with you

1Name the salt formed (Getting started)

2Complete the general word equations (Getting started)

3Balance an acid + metal equation (Building confidence)

4Acid + base, name salt and balance (Building confidence)

5Acid + carbonate with the gas test (Stretch)

6Predict, name and balance for an unfamiliar acid (Stretch)

Acid

Base

Salt

Neutralisation

Metal carbonate

Chloride

Sulfate

Nitrate

Test for hydrogen

Test for carbon dioxide

✕Writing acid + carbonate → salt + carbon dioxide and forgetting the water

✕Giving a vague gas test such as 'it pops' or 'it changes colour'

✕Writing hydrogen as H instead of H₂

✕Getting the salt formula wrong, e.g. writing MgCl or ZnCl instead of MgCl₂ / ZnCl₂

✕Saying copper (or silver/gold) reacts with dilute acid to give hydrogen

✕Writing 'sulphate' or confusing nitrate with nitrite