Stoichiometry

Learn and apply Stoichiometry in the published Chemistry course sequence.

GCE A-Level H2 Chemistry 9476-2027

Learning goals

Mole and Avogadro Constant
Empirical and Molecular Formula
Reacting Masses and Limiting Reagent
Solution Concentration and Dilution
Titration Calculations
Gas Calculations (pV = nRT)

H2 Stoichiometry learning outcomes

This hub is the fastest way to gain marks: it turns calculation questions into a repeatable workflow.

Before you start

Beginner path: follow the Lessons (Recommended Order) from top to bottom.

Revision: Jump to: Quick Reference · What You Must Memorise · Common Exam Traps · Hub Quiz.

Prerequisites: skim the Prerequisites list first if you’re rusty.

Useful links: A Level portal · Exam Skills

What You’ll Learn

Convert cleanly between mass, moles, concentration, and gas volume.
Set up limiting reagent and titration calculations with correct units and sig figs.
Show working in a way that earns method marks even if the final number is wrong.

Lessons (Recommended Order)

Mole and Avogadro Constant
Particles ↔ moles, mass ↔ moles.
Open lesson
Empirical and Molecular Formula
Convert composition data into formulae.
Open lesson
Reacting Masses and Limiting Reagent
Limiting reagent, yield, leftovers.
Open lesson
Solution Concentration and Dilution
n = cV, unit conversions, dilution rule.
Open lesson
Titration Calculations
Standard method marks, ratio discipline.
Open lesson
Gas Calculations (pV = nRT)
Gas moles plus reaction stoichiometry.
Open lesson

Quick Reference

What you need	Use	Unit check
universal workflow	balance → convert to moles → ratio → convert to asked quantity	units and sig figs stay consistent
particles ↔ moles	N = nN_A	N_A = 6.02 × 10²³ mol⁻¹ (Data Booklet)
mass ↔ moles	n = m/M	M in g mol⁻¹
solution moles	n = cV	V in dm³
dilution	c₁V₁ = c₂V₂	same solute only (no reaction)
gas moles	pV = nRT	T in K; match units to R
common R values	8.314 J mol⁻¹K⁻¹ with Pa and m³; 8.314 kPa dm³ mol⁻¹K⁻¹ with kPa and dm³	pick R to match your units
titration data	mean of concordant titres; ignore rough; record burette to 2 d.p.	check question’s concordance tolerance

What You Must Memorise

N = nN_A and n = N/N_A (state the entity: atoms/molecules/ions/formula units).
n = m/M (use M in g mol⁻¹; don’t treat Mᵣ as a unit).
n = cV with V in dm³ (convert: 1000 cm³ = 1 dm³).
c₁V₁ = c₂V₂ is for dilution only (no reaction; same solute).
pV = nRT with T in K and R matching your p and V units.
Sig figs: keep 3–4 s.f. through working; round at the end unless instructed.

Hub Quiz and Check Your Understanding

Use the quiz without notes first. If an answer fails, identify whether the broken link is the chemical equation, quantity-to-mole conversion, ratio, unit conversion or final significant figures before revisiting the lesson.

H2 Stoichiometry Hub Quiz
Check mole conversions, formulae, reacting quantities, solutions, titrations and ideal-gas calculations.
Start hub quiz
H2 Stoichiometry Knowledge Check
Find the calculation step that needs more work, use the feedback, then try a fresh question independently.
Practice onlyCheck understanding

Practise

Work through questions with marking and feedback as you learn.

About 10 minutes

Questions are picked at random each time you start. You'll see the answer after each question. It's for practice only and doesn't count towards mastery.

Recent attempts

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This check needs JavaScript to record answers. The reviewed questions are listed below for study.

What is the total number of ions in 5.85 g of sodium chloride (Mᵣ 58.5)? (L = 6.02 × 10²³ mol⁻¹)

1.20 × 10²³
6.02 × 10²²
3.52 × 10²⁴
7.04 × 10²⁴

Boron consists of ¹⁰B (10.0, 19.9 %) and ¹¹B (11.0, 80.1 %). What is the relative atomic mass of boron, and what is the value 11.0 for ¹¹B called?

10.8; 11.0 is the relative isotopic mass of boron-11
10.5; 11.0 is the relative isotopic mass of boron-11
10.2; 11.0 is the relative isotopic mass of boron-11
10.8; 11.0 is the relative atomic mass of boron-11

0.600 g of a hydrocarbon burns completely to give 1.76 g of CO₂ and 1.08 g of H₂O. Its Mᵣ is 30. What are its empirical and molecular formulae?

Empirical formula CH₃; molecular formula C₂H₆
Empirical formula C₂H₃; molecular formula C₂H₃
Empirical formula C₂H₆; molecular formula C₂H₆
Empirical formula CH₃; molecular formula CH₃

Aqueous iron(III) ions react with aqueous hydroxide ions to form a precipitate of iron(III) hydroxide. Which is the balanced ionic equation?

Fe³⁺(aq) + 3OH⁻(aq) → Fe(OH)₃(s)
Fe³⁺(aq) + OH⁻(aq) → Fe(OH)₃(s)
FeCl₃(aq) + 3NaOH(aq) → Fe(OH)₃(s) + 3NaCl(aq)
Fe³⁺(aq) + 3OH⁻(aq) → Fe(OH)₃(aq)

5.00 g of zinc (Aᵣ 65.4) is heated with 4.00 g of sulfur (Aᵣ 32.1): Zn + S → ZnS. Which reactant is in excess, and what mass of it remains?

Sulfur; 1.55 g remains
Zinc; 1.00 g remains
Sulfur; 0.0482 g remains
Sulfur; 3.15 g remains

What mass of anhydrous sodium carbonate (Mᵣ 106.0) is needed to make 250 cm³ of a 0.100 mol dm⁻³ solution?

2.65 g
2650 g
10.6 g
26.5 g

3.575 g of hydrated sodium carbonate, Na₂CO₃·xH₂O, is dissolved and made up to 250 cm³. 25.0 cm³ of this solution needs 25.00 cm³ of 0.100 mol dm⁻³ HCl: Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂. What is x? (Mᵣ Na₂CO₃ = 106.0, H₂O = 18.0)

0.654 g of zinc (Aᵣ 65.4) reacts with excess acid: Zn + 2H⁺ → Zn²⁺ + H₂. What volume of hydrogen forms at 101 kPa and 298 K? (R = 8.31 J K⁻¹ mol⁻¹)

245 cm³
0.245 cm³
490 cm³
20.6 cm³

Practise after feedback

After a check, practise the skills it showed you need to work on.

About 10 minutes

Questions are picked at random each time you start. You'll see the answer after each question. It's for practice only and doesn't count towards mastery.

Recent attempts

History is stored only in this browser.

No completed attempts are saved yet.

This check needs JavaScript to record answers. The reviewed questions are listed below for study.

What is the total number of ions in 5.85 g of sodium chloride (Mᵣ 58.5)? (L = 6.02 × 10²³ mol⁻¹)

1.20 × 10²³
6.02 × 10²²
3.52 × 10²⁴
7.04 × 10²⁴

Boron consists of ¹⁰B (10.0, 19.9 %) and ¹¹B (11.0, 80.1 %). What is the relative atomic mass of boron, and what is the value 11.0 for ¹¹B called?

10.8; 11.0 is the relative isotopic mass of boron-11
10.5; 11.0 is the relative isotopic mass of boron-11
10.2; 11.0 is the relative isotopic mass of boron-11
10.8; 11.0 is the relative atomic mass of boron-11

0.600 g of a hydrocarbon burns completely to give 1.76 g of CO₂ and 1.08 g of H₂O. Its Mᵣ is 30. What are its empirical and molecular formulae?

Empirical formula CH₃; molecular formula C₂H₆
Empirical formula C₂H₃; molecular formula C₂H₃
Empirical formula C₂H₆; molecular formula C₂H₆
Empirical formula CH₃; molecular formula CH₃

Aqueous iron(III) ions react with aqueous hydroxide ions to form a precipitate of iron(III) hydroxide. Which is the balanced ionic equation?

Fe³⁺(aq) + 3OH⁻(aq) → Fe(OH)₃(s)
Fe³⁺(aq) + OH⁻(aq) → Fe(OH)₃(s)
FeCl₃(aq) + 3NaOH(aq) → Fe(OH)₃(s) + 3NaCl(aq)
Fe³⁺(aq) + 3OH⁻(aq) → Fe(OH)₃(aq)

5.00 g of zinc (Aᵣ 65.4) is heated with 4.00 g of sulfur (Aᵣ 32.1): Zn + S → ZnS. Which reactant is in excess, and what mass of it remains?

Sulfur; 1.55 g remains
Zinc; 1.00 g remains
Sulfur; 0.0482 g remains
Sulfur; 3.15 g remains

What mass of anhydrous sodium carbonate (Mᵣ 106.0) is needed to make 250 cm³ of a 0.100 mol dm⁻³ solution?

2.65 g
2650 g
10.6 g
26.5 g

0.654 g of zinc (Aᵣ 65.4) reacts with excess acid: Zn + 2H⁺ → Zn²⁺ + H₂. What volume of hydrogen forms at 101 kPa and 298 K? (R = 8.31 J K⁻¹ mol⁻¹)

245 cm³
0.245 cm³
490 cm³
20.6 cm³

Check what I know

Start here to see which parts you already know.

About 8 minutes

Answer 8 short questions. It shows what to work on next and doesn't count towards mastery.

Recent attempts

History is stored only in this browser.

No completed attempts are saved yet.

This check needs JavaScript to record answers. The reviewed questions are listed below for study.

How many hydrogen atoms are there in 0.250 mol of ethane, C₂H₆? (Avogadro constant L = 6.02 × 10²³ mol⁻¹)

9.03 × 10²³
1.51 × 10²³
1.20 × 10²⁴
3.01 × 10²³

Chlorine consists of ³⁵Cl (relative isotopic mass 35.0, abundance 75.8 %) and ³⁷Cl (relative isotopic mass 37.0, abundance 24.2 %). Which statement gives the relative atomic mass of chlorine and its meaning?

35.5; the weighted mean mass of the atoms of chlorine relative to 1/12 of the mass of an atom of carbon-12
36.0; the weighted mean mass of the atoms of chlorine relative to 1/12 of the mass of an atom of carbon-12
36.5; the weighted mean mass of the atoms of chlorine relative to 1/12 of the mass of an atom of carbon-12
35.5; the mass in grams of one chlorine atom

A compound contains 40.0 % carbon, 6.7 % hydrogen and 53.3 % oxygen by mass, and its relative molecular mass is 180. What are its empirical formula and molecular formula?

Empirical formula CH₂O; molecular formula C₆H₁₂O₆
Empirical formula C₆H₁₂O₆; molecular formula CH₂O
Empirical formula CH₂O; molecular formula CH₂O
Empirical formula C₃H₆O₃; molecular formula C₆H₁₂O₆

Aqueous aluminium sulfate reacts with aqueous sodium hydroxide to form a precipitate of aluminium hydroxide and aqueous sodium sulfate. Which equation is balanced?

Al₂(SO₄)₃(aq) + 6NaOH(aq) → 2Al(OH)₃(s) + 3Na₂SO₄(aq)
Al₂(SO₄)₃(aq) + 3NaOH(aq) → 2Al(OH)₃(s) + 3Na₂SO₄(aq)
Al₂(SO₄)₃(aq) + 6NaOH(aq) → Al(OH)₃(s) + 3Na₂SO₄(aq)
Al₂(SO₄)₃(aq) + 6NaOH(aq) → 2Al(OH)₃(s) + 6NaSO₄(aq)

2.70 g of aluminium (Aᵣ 27.0) is heated with 7.10 g of chlorine (Mᵣ 71.0): 2Al + 3Cl₂ → 2AlCl₃. What is the maximum mass of AlCl₃ (Mᵣ 133.5) formed?

8.90 g
13.4 g
20.0 g
9.80 g

25.0 cm³ of 2.00 mol dm⁻³ hydrochloric acid is diluted with water to a total volume of 250 cm³. What is the concentration of the diluted acid (Mᵣ HCl = 36.5)?

0.200 mol dm⁻³, which is 7.30 g dm⁻³
0.182 mol dm⁻³, which is 6.64 g dm⁻³
20.0 mol dm⁻³, which is 730 g dm⁻³
0.200 mol dm⁻³, which is 0.00548 g dm⁻³

25.0 cm³ of a 0.0400 mol dm⁻³ solution of an acid reacts exactly with 20.0 cm³ of 0.100 mol dm⁻³ sodium hydroxide. How many moles of NaOH react with one mole of the acid?

2, so each acid molecule provides two H⁺ ions
2.5, from 0.100 ÷ 0.0400
0.5, from 1.00 × 10⁻³ ÷ 2.00 × 10⁻³
1.25, from 25.0 ÷ 20.0

Calcium carbonate (Mᵣ 100.1) decomposes: CaCO₃ → CaO + CO₂. What mass of CaCO₃ gives 0.500 dm³ of CO₂ at 100 kPa and 27 °C? (R = 8.31 J K⁻¹ mol⁻¹)

2.01 g
22.3 g
2.01 × 10³ g
2.09 g

Check my progress

When you feel ready, answer on your own to show what you can do.

About 10 minutes

Answer 8 questions. You'll see your score, the answers and explanations at the end. Your result can count towards your course progress.

Recent attempts

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No completed attempts are saved yet.

Check again

After practising what your progress check showed, check those skills again.

About 10 minutes

Answer 8 questions. You'll see your score, the answers and explanations at the end. Your result can count towards your course progress.

Recent attempts

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No completed attempts are saved yet.

Review

Come back later to see whether your learning has lasted.

About 10 minutes

Answer 8 questions. You'll see your score, the answers and explanations at the end. A scheduled review counts towards your course progress only when it is due.

Recent attempts

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No completed attempts are saved yet.

Stoichiometry

H2 Stoichiometry learning outcomes

What You’ll Learn

Lessons (Recommended Order)

Mole and Avogadro Constant

Empirical and Molecular Formula

Reacting Masses and Limiting Reagent

Solution Concentration and Dilution

Titration Calculations

Gas Calculations (pV = nRT)

Quick Reference

What You Must Memorise

Hub Quiz and Check Your Understanding

H2 Stoichiometry Hub Quiz

H2 Stoichiometry Knowledge Check

Practise

Practice complete

Your answers

Practise after feedback

Practice complete

Your answers

Check what I know

Starting check complete

Your answers

Check my progress

Progress check complete

Your answers

Check again

Progress check complete

Your answers

Review

Review complete

Your answers