CCEA GCSE Chemistry
CCEA GCSE Chemistry 1.5 Symbols, Formulae and Equations Exam Questions
Free CCEA GCSE Chemistry revision for 1.5 Symbols, Formulae and Equations: what you need to know, common mistakes and exam-style questions with answers. Covers writing chemical formulae from ions and valencies, word equations, balanced symbol equations, ionic equations, half equations and state symbols.
Practise 1.5 Symbols, Formulae and Equations with past papers
Once you have learnt this topic, find the 1.5 Symbols, Formulae and Equations questions in real CCEA GCSE Chemistry past papers and mark them with the mark scheme. Doing lots of real questions is the quickest way to learn how examiners ask about each idea.
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About CCEA GCSE Chemistry 1.5 Symbols, Formulae and Equations
Symbols, Formulae and Equations is a skills topic in CCEA GCSE Chemistry Unit 1 that is used across the whole course. You need to work out the formulae of compounds from the charges on ions or from valencies, including compound ions such as sulfate, nitrate, carbonate, hydroxide and ammonium. You must write word equations, balanced symbol equations with state symbols, ionic equations and, at Higher tier, half equations. Almost every other topic, from acids to electrolysis, tests these skills, so errors here cost marks throughout both written papers. Examiners regularly report incorrect formulae, incorrect use of subscripts and missing state symbols as common reasons for lost marks.
What you need to know
- Formulae of ionic compounds Balance the charges so the total is zero. For example Ca2+ and Cl- give CaCl2, and Al3+ and O2- give Al2O3. Use brackets for more than one compound ion, for example Ca(OH)2 and (NH4)2SO4.
- Common ions to learn Hydroxide OH-, nitrate NO3-, sulfate SO4 2-, carbonate CO3 2-, hydrogencarbonate HCO3-, ammonium NH4+. Group 1 ions are 1+, Group 2 ions are 2+, Group 7 ions are 1- and Group 6 ions are 2-.
- Balancing equations Write correct formulae first, then balance by changing only the large numbers in front of formulae. For example 2Na + 2H2O → 2NaOH + H2. Never change subscripts in a formula to balance.
- State symbols (s) solid, (l) liquid, (g) gas and (aq) aqueous, meaning dissolved in water. Water is (l), and precipitates are (s).
- Ionic equations Show only the ions that react, leaving out spectator ions. Neutralisation: H+(aq) + OH-(aq) → H2O(l). Precipitation: Ag+(aq) + Cl-(aq) → AgCl(s).
- Half equations Show electron gain or loss at an electrode or in redox, for example Cu2+ + 2e- → Cu and 2Cl- → Cl2 + 2e-. Charges must balance on both sides.
Common mistakes in 1.5 Symbols, Formulae and Equations
- Changing subscripts to balance an equation, for example writing H2O2 instead of putting 2 in front of H2O.
- Forgetting brackets around compound ions, for example writing CaOH2 instead of Ca(OH)2.
- Writing diatomic elements as single atoms. Hydrogen, oxygen, nitrogen and the halogens are H2, O2, N2, F2, Cl2, Br2 and I2.
- Including spectator ions in ionic equations or leaving the charges unbalanced.
- Writing aq for water or for a precipitate. Water is (l) and an insoluble solid formed in solution is (s).
Try three 1.5 Symbols, Formulae and Equations exam-style questions
1. Write the formula of aluminium sulfate. (1 mark)
Show the mark scheme answer
Al2(SO4)3.
2. Write a balanced symbol equation, with state symbols, for the reaction of magnesium with dilute hydrochloric acid. (3 marks)
Show the mark scheme answer
Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g); correct formulae; correct balancing and state symbols.
3. Write the ionic equation, with state symbols, for the formation of a precipitate when silver nitrate solution is added to sodium chloride solution. (2 marks)
Show the mark scheme answer
Ag+(aq) + Cl-(aq) → AgCl(s); correct state symbols.
1.5 Symbols, Formulae and Equations FAQs
What does CCEA GCSE Chemistry 1.5 Symbols, Formulae and Equations cover?
It covers writing formulae from ions and valencies, word and balanced symbol equations, state symbols, ionic equations and half equations.
Which unit is 1.5 Symbols, Formulae and Equations examined in?
It sits in Unit 1, but the skills are tested throughout both the Unit 1 and Unit 2 written papers and in practical questions.
How do I learn formulae quickly?
Learn the charges of the common ions by heart, then practise swapping and simplifying charges to build formulae. Writing ten formulae a day for a week is very effective.
