CCEA A Level Chemistry

CCEA A Level Chemistry 1.1 Formulae, Equations and Amounts of Substance Exam Questions

Free CCEA A Level Chemistry revision for 1.1 Formulae, Equations and Amounts of Substance: what you need to know, common mistakes and exam-style questions with answers. Covers ionic formulae, polyatomic ions, balancing full and ionic equations, the mole, reacting masses, limiting reagents and water of crystallisation.

Practise 1.1 Formulae, Equations and Amounts of Substance with past papers

Once you have learnt this topic, find the 1.1 Formulae, Equations and Amounts of Substance questions in real CCEA A Level 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 A Level Chemistry 1.1 Formulae, Equations and Amounts of Substance

Section 1.1 is the first section of Unit AS 1 and the foundation for every calculation on the CCEA course. You need to write formulae from ions, including a long list of polyatomic ions that CCEA expects you to recall (such as thiosulfate, hypochlorite, chlorate, dichromate and permanganate), balance unfamiliar equations and write ionic equations with state symbols. You also need the mole, the Avogadro constant and molar mass, reacting mass calculations with limiting and excess reagents, and finding the number of moles of water of crystallisation. These skills reappear in titrations (1.9), gas volumes and yields (2.1) and A2 volumetric analysis.

What you need to know

  • Polyatomic ions Learn the formulae and charges of sulfate SO4 2-, sulfite SO3 2-, thiosulfate S2O3 2-, hydrogensulfate HSO4 -, hydrogencarbonate HCO3 -, carbonate CO3 2-, nitrate NO3 -, nitrite NO2 -, phosphate PO4 3-, chlorate(V) ClO3 -, hypochlorite ClO -, hydroxide OH -, dichromate Cr2O7 2-, chromate CrO4 2-, permanganate MnO4 - and ammonium NH4 +.
  • Equations Balance atoms and charges. Ionic equations show only the species that react, for example H+(aq) + OH-(aq) gives H2O(l). Always include state symbols when asked.
  • The mole One mole contains 6.02 x 10^23 particles (the Avogadro constant). Moles = mass / molar mass, and molar mass is in g mol-1.
  • Reacting masses Convert mass to moles, use the mole ratio from the balanced equation, then convert back. The limiting reagent is the one that runs out first; the other is in excess.
  • Water of crystallisation Hydrated salts contain water in the crystal; anhydrous salts do not. Heat to constant mass, then find moles of anhydrous salt and moles of water lost to find x in a formula such as CuSO4.xH2O.

Common mistakes in 1.1 Formulae, Equations and Amounts of Substance

  • Writing hypochlorite or chlorate(V) incorrectly. Hypochlorite (chlorate(I)) is ClO- and chlorate(V) is ClO3-.
  • Leaving spectator ions in an ionic equation. Remove ions that appear unchanged on both sides.
  • Not heating to constant mass in a water of crystallisation experiment. Repeat heating and weighing until two readings agree.
  • Using the mass ratio instead of the mole ratio. Always convert to moles before using the equation.
  • Rounding too early in multi-step calculations. Keep at least three significant figures until the final answer.

Try three 1.1 Formulae, Equations and Amounts of Substance exam-style questions

1. Calculate the mass of magnesium oxide formed when 3.00 g of magnesium burns completely in oxygen. (3 marks)

Show the mark scheme answer

Moles Mg = 3.00 / 24.3 = 0.123; 2Mg + O2 gives 2MgO so moles MgO = 0.123; mass = 0.123 x 40.3 = 4.98 g (4.97 to 4.98 g accepted).

2. 2.50 g of hydrated copper(II) sulfate, CuSO4.xH2O, was heated to constant mass, leaving 1.60 g of anhydrous CuSO4. Find x. (3 marks)

Show the mark scheme answer

Mass of water = 0.90 g; moles CuSO4 = 1.60 / 159.6 = 0.0100; moles H2O = 0.90 / 18.0 = 0.050; ratio 0.0100 : 0.050 = 1 : 5, so x = 5.

3. Write an ionic equation, with state symbols, for the reaction of aqueous silver nitrate with aqueous sodium chloride. (2 marks)

Show the mark scheme answer

Ag+(aq) + Cl-(aq) gives AgCl(s); correct state symbols.

1.1 Formulae, Equations and Amounts of Substance FAQs

What does CCEA A Level Chemistry 1.1 Formulae, Equations and Amounts of Substance cover?

It covers ionic formulae and polyatomic ions, balanced full and ionic equations, the mole and Avogadro constant, reacting masses and water of crystallisation.

Which unit is 1.1 examined in?

It is examined in Unit AS 1: Basic Concepts in Physical and Inorganic Chemistry, a 1 hour 30 minute paper with a multiple-choice section and structured questions. Related practical skills can also be assessed in Unit AS 3.

Which ions do I need to learn for CCEA?

CCEA expects you to recall a set of polyatomic ions including sulfite, thiosulfate, hydrogensulfate, nitrite, phosphate, chlorate, hypochlorite, chromate, dichromate and permanganate. Make flashcards and test yourself until you can write each formula and charge instantly.