🎯 Common Question Types
- "Balance the following equation" — 1 or 2 marks: always check every element
- "Explain the apparent decrease/increase in mass" — 3 marks: say gas escapes/enters AND state mass is conserved
- "Write the formula of compound X" — 1 mark: use charge-and-swap rule for ionic, memorise covalent names
- Calculation questions link conservation of mass to moles: if 40 g X makes Y, the masses must balance
📝 Key Command Words
- Balance — add coefficients only (never change subscripts)
- Write the formula — apply ionic charge rule or recall covalent formula
- Explain — state the cause AND effect (gas escapes → less mass on balance)
- State symbols — always (s), (l), (g), (aq) — never abbreviate differently
⚠️ Common Mistakes to Avoid
- Changing subscripts instead of adding coefficients — instant mark loss
- Saying "mass is lost" when a gas escapes — mass is NEVER lost, it just leaves the container
- Forgetting brackets around polyatomic ions: Mg(OH)₂ not MgOH₂
- Writing HO instead of OH for hydroxide, or SO₄ without the 2− charge in ionic equations
- Forgetting to simplify ionic formulae: not Ca₂O₂, but CaO
This exam tips covers Exam Tips within Formulae, Equations and Conservation of Mass for GCSE Chemistry. Revise Formulae, Equations and Conservation of Mass in Quantitative Chemistry for GCSE Chemistry with 13 exam-style questions and 12 flashcards. This topic shows up very often in GCSE exams, so students should be able to explain it clearly, not just recognise the term. It is section 13 of 14 in this topic. Treat this as a marking guide for what examiners are looking for, not just a fact list.
Practice questions for Formulae, Equations and Conservation of Mass
Which of the following is the correct formula for oxygen gas?
Explain why mass is conserved in a chemical reaction.
Quick recall flashcards
Name the seven diatomic elements.
H₂, N₂, O₂, F₂, Cl₂, Br₂, I₂
Mnemonic: Have No Fear Of Ice Cold Beer
State the law of conservation of mass.
In a chemical reaction, the total mass of the products equals the total mass of the reactants.
No atoms are created or destroyed — they are only rearranged.