Edexcel GCSE Chemistry
Edexcel GCSE Chemistry Topic 0: Formulae, Equations and Hazards Exam Questions
Free Edexcel GCSE Chemistry exam questions for Topic 0: Formulae, Equations and Hazards, with a mark scheme for every pack. Covers formulae of elements, compounds and ions, balanced and ionic equations with state symbols, hazard symbols and reducing risk.
Topic 0: Formulae, Equations and Hazards exam questions
3 question packs of real past exam questions, each with its mark scheme. Do not stop after a few: answer as many as you can without notes, then mark every answer with the mark scheme. The more questions you do, the more quickly you will spot how examiners ask about each idea.
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About Edexcel GCSE Chemistry Topic 0: Formulae, Equations and Hazards
Topic 0 of Edexcel GCSE Chemistry is a set of core skills rather than a block of new chemistry. It covers writing formulae for elements, simple compounds and ions, writing word equations and balanced symbol equations with state symbols, writing ionic equations at Higher tier, and using hazard symbols and risk assessment in practical work. Because these skills underpin everything else, Topic 0 can be assessed on both Paper 1 and Paper 2. Examiners rarely ask about it in isolation; instead, almost every question on acids, electrolysis, metals or organic chemistry expects correct formulae and balanced equations, and practical questions ask how to reduce a named risk.
What you need to know
- Formulae of elements Most elements are written as single atoms, for example Na, Fe and C, but some exist as diatomic molecules: H2, N2, O2, F2, Cl2, Br2 and I2.
- Formulae of ions and compounds Learn common ions: Na+, K+, Mg2+, Ca2+, Al3+, NH4+, Cl-, O2-, OH-, NO3-, SO4 2-, CO3 2-. Balance the charges to get the formula, for example Ca(OH)2, Al2(SO4)3 and (NH4)2SO4.
- Word and symbol equations A balanced equation has the same number of each type of atom on both sides. Change only the numbers in front of formulae, never the formulae themselves.
- State symbols (s) solid, (l) liquid, (g) gas and (aq) aqueous solution, for example Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g).
- Ionic equations (Higher tier only) Show only the ions and substances that change, leaving out spectator ions. Examples: H+(aq) + OH-(aq) → H2O(l); Ag+(aq) + Cl-(aq) → AgCl(s).
- Hazards and risk Hazard symbols on containers warn of dangers such as toxic, corrosive, flammable, oxidising, harmful or irritant, and environmental hazard. Reduce risk by using lower concentrations, smaller quantities, eye protection, gloves, a fume cupboard or a water bath instead of a flame.
Common mistakes in Topic 0: Formulae, Equations and Hazards
- Writing Cl or O instead of Cl2 or O2 for gaseous elements in equations.
- Changing subscripts to balance an equation, which changes the substance itself.
- Forgetting brackets around polyatomic ions, for example writing CaOH2 instead of Ca(OH)2.
- Using (l) for a solution. Something dissolved in water is (aq); (l) is only for pure liquids such as water or molten substances.
- Describing a hazard instead of a precaution. A risk-reduction answer should state an action and why, for example 'wear eye protection because the acid is corrosive'.
Try three Topic 0: Formulae, Equations and Hazards exam-style questions
1. Write the formula of aluminium sulfate. (1 mark)
Show the mark scheme answer
Al2(SO4)3.
2. Balance the equation and add state symbols: Na + H2O → NaOH + H2. (2 marks)
Show the mark scheme answer
2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g); balancing (1), state symbols (1).
3. Write the ionic equation for the reaction between silver nitrate solution and sodium chloride solution. (2 marks) Higher tier only
Show the mark scheme answer
Ag+(aq) + Cl-(aq) → AgCl(s); correct species (1), state symbols (1).
Topic 0: Formulae, Equations and Hazards FAQs
What does Edexcel GCSE Chemistry Topic 0 cover?
It covers formulae of elements, compounds and ions, word and balanced symbol equations with state symbols, ionic equations at Higher tier, hazard symbols and ways to reduce risk in experiments.
Which paper is Topic 0 examined in?
Topic 0 is not a separate paper section; its skills are assessed throughout both Paper 1 and Paper 2.
Which ions should I memorise for formulae?
Learn the common positive ions (including NH4+ and Al3+) and negative ions including OH-, NO3-, SO4 2- and CO3 2-. Practise writing formulae by balancing charges until it is automatic.
