1ePrinciples of Chemistry

Chemical formulae, equations and calculations — Edexcel Linear - OL (Chemistry) Revision Notes & Topical Questions

20 min read 31 parts Lesson 5 of 25 Unit quiz

📚 Edexcel Linear - OL (Chemistry) Hub / Topical Revision

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Lesson summary

Chemical formulae, equations and calculations Edexcel O Level Linear Chemistry notes: write word equations and balanced chemical equations (including state symbols): - for reactions studied in this specification - for unfamiliar reactions where suitable information is provided.

Empirical formula
Chemical formulae, equations and calculations Edexcel O Level Linear Chemistry: what to do next
Relative atomic mass (Ar)
Molar mass
Molecular formula
Concentration

Part 1 of 6Key ideas

Titration

Titration n(acid) from c × V, then use ratio.

Empirical formula

Empirical formula divide % by Ar, then divide by smallest.

Mass spectrometry gives relative isotopic masses and abundances.

Part 2 of 6Syllabus points

write word equations and balanced chemical equations (including state symbols): - for reactions studied in this specification - for unfamiliar reactions where suitable information is provided. calculate relative formula masses (including relative molecular masses) (Mr) from relative atomic masses (Ar)

know that the mole (mol) is the unit for the amount of a substance

understand how to carry out calculations involving amount of substance, relative atomic mass (Ar) and relative formula mass (Mr)

calculate reacting masses using experimental data and chemical equations

calculate percentage yield

understand how the formulae of simple compounds can be obtained experimentally, including metal oxides, water and salts containing water of crystallisation

know what is meant by the terms empirical formula and molecular formula

calculate empirical and molecular formulae from experimental data

practical: know how to determine the formula of a metal oxide by combustion (e.g. magnesium oxide) or by reduction (e.g. copper(II) oxide)

Part 3 of 6Process & sequence

Write the balanced equation.

Find moles of the known substance.

Use the mole ratio.

Convert to the required quantity.

Give answer to correct significant figures.

Mass
÷ M
Moles
× ratio
Moles of product
× M
Mass

Part 4 of 6Summary

What the symbols mean:

n = m ÷ M.

What the symbols mean: n = amount of substance (mol) · m = mass (g) · M or M_r = molar mass (g mol⁻¹, numerically equal to M_r)

What the symbols mean:

n = c × V (V in dm³).

What the symbols mean: c = concentration (mol dm⁻³) · n = amount (mol) · V = volume (dm³; divide cm³ by 1000)

Part 5 of 6Keep going

Chemical formulae, equations and calculations Edexcel O Level Linear Chemistry: what to do next

These Chemical formulae, equations and calculations Edexcel O Level Linear Chemistry notes covered the key ideas, worked examples and exam technique for this topic. Check your Chemical formulae, equations and calculations Edexcel O Level Linear Chemistry understanding with the practice questions below, then reread any Chemical formulae, equations and calculations Edexcel O Level Linear Chemistry point you were unsure about before moving on.

Practice: Chemical formulae, equations and calculations Edexcel O Level Linear Chemistry practice questions

Previous lesson: 1d The Periodic Table — Notes

Next lesson: 1f Ionic bonding — Notes

Course: Edexcel Linear – OL (chemistry) — all units

Official syllabus: Pearson Edexcel International GCSEs

Part 6 of 6Compare: Compare

Key mole calculations
Quantity	Formula	Units	Example	Answer	Tip
Moles from mass	n = m ÷ M	mol	9.0 g of H₂O (M = 18)	0.50 mol	Use g and g mol⁻¹
Moles from solution	n = c × V	mol	25.0 cm³ of 0.100 mol dm⁻³	2.50 × 10⁻³ mol	Convert cm³ ÷ 1000
Moles of gas	n = V ÷ 24	mol	1.2 dm³ at r.t.p.	0.050 mol	Or pV = nRT
Ideal gas equation	pV = nRT	Pa, m³, K	—	—	R = 8.31 J K⁻¹ mol⁻¹
Percentage yield	actual ÷ theoretical × 100	%	—	—	Less than 100% due to losses
Atom economy	Mr desired ÷ Mr all products × 100	%	—	—	Higher = less waste

Key terms

Command terms

Give / State / Name

Recall a fact; one idea per mark.

Define

Give the exact meaning using the specification keywords.

Describe

Give an account of what happens / the pattern in data, quoting values; no reasons needed.

Explain

Give reasons with linked statements (cause → effect). Each linked step is usually a separate marking point.

Suggest

Use knowledge in a new context; more than one answer may be accepted.

Compare

Similarities and differences; each point must refer to both items.

Calculate

Show working; include units; check significant figures. Method marks are given even if the final answer is wrong.

Discuss

Explore the issue from different angles and link the points.

Evaluate / Assess

Weigh strengths and weaknesses and reach a supported judgement.

Deduce

Draw a conclusion from the information given.

Justify

Support a statement/choice with evidence.

Exam technique

Keywords the mark scheme looks for in this lesson

Mole · Relative atomic mass (Ar) · Molar mass · Empirical formula · Molecular formula · Concentration · Molar gas volume · Limiting reagent

Learn each definition in the Key words tab exactly; a missing keyword in a definition usually loses the mark.

How to get full marks (examiner guidance)

Use specification keywords exactly (e.g. electronegativity, nucleophile, dynamic equilibrium, activation energy).

Link ideas

Link ideas for “explain” each marking point is usually a cause → consequence step; unlinked facts often score nothing.

Use the information in the question

“discuss/evaluate” answers must use the data provided and match the number of marks.

Convert units carefully (mg → g, cm³ → dm³) and show working for calculations.

Avoid vague words

“it”, “stuff”, “things”, “goes up”, “energy is made”. Name the substance and the process.

Do not extrapolate a graph line beyond the data or to zero unless asked.

Six-mark extended responses are marked on content AND a logical, linked line of reasoning.

Last updated: 18 October 2026