1. 1
   A laboratory technician prepares a model of a molecule using coloured balls to represent atoms and sticks to represent bonds: the model shows one central carbon atom joined to four separate hydrogen atoms, with no other atoms present.

   (a)

   What is the molecular formula of this compound?

   [1 mark]

   • ACH4
   • BCH3
   • CC4H
   • DC2H4

   (b)

   The technician then builds a word equation model showing methane reacting completely with oxygen gas to form carbon dioxide gas and water. Which of the following correctly represents this reaction as a word equation?

   [1 mark]

   • AMethane + carbon dioxide $\rightarrow$ oxygen + water
   • BMethane + oxygen $\rightarrow$ carbon dioxide + water
   • CWater + oxygen $\rightarrow$ methane + carbon dioxide
   • DCarbon dioxide + water $\rightarrow$ methane + oxygen

   (c)

   State what is meant by the term molecular formula, and explain what information it gives about a compound such as methane, CH4.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A chemistry student is given a diagrammatic model of an ionic compound showing 1 magnesium ion, Mg2+, surrounded by 2 chloride ions, Cl−, in the correct ratio needed for the compound to be electrically neutral overall.

   (a)

   What is the formula of this ionic compound?

   [1 mark]

   • AMg2Cl
   • BMgCl
   • CMgCl2
   • DMg2Cl2

   (b)

   The student is then given a model of a different ionic compound showing 2 sodium ions, Na+, and 1 oxide ion, O2−, combined in the ratio required for overall electrical neutrality. What is the formula of this compound?

   [1 mark]

   • ANa2O2
   • BNaO2
   • CNaO
   • DNa2O

   (c)

   Explain how the charges on the ions in an ionic compound are used to deduce its formula, using magnesium oxide (Mg2+ and O2−) as an example.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A fertiliser company reacts nitric acid with sodium hydroxide solution to produce sodium nitrate solution and water, as part of quality control testing for their sodium nitrate fertiliser product.

   (a)

   Construct a balanced word equation for this reaction, and construct the balanced symbol equation, including state symbols, given that nitric acid is HNO3(aq), sodium hydroxide is NaOH(aq), sodium nitrate is NaNO3(aq) and water is H2O(l).

   [3 marks]

   (b)

   The company also produces ammonium sulfate fertiliser by reacting ammonium ions, NH4+, with sulfate ions, SO4^2-. Deduce the formula of ammonium sulfate, explaining how you use the charges on the ions to determine the correct ratio, and define the term empirical formula, stating whether the formula you have deduced for ammonium sulfate is also its empirical formula.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A cement manufacturer heats calcium carbonate, CaCO3(s), strongly in a kiln, causing it to thermally decompose into calcium oxide, CaO(s), and carbon dioxide gas, CO2(g).

   (a)

   Construct the balanced word equation and the balanced symbol equation, including state symbols, for this reaction, and explain fully how you checked that the symbol equation you have written is balanced, referring to the number of each type of atom on both sides of the equation.

   [6 marks]

   (b)

   The manufacturer's laboratory analyses a sample and determines it contains only calcium, oxygen and carbon atoms in the ratio 1 : 3 : 1 (calcium : oxygen : carbon). Explain what is meant by the term empirical formula, deduce the empirical formula of this compound from the given atom ratio, and explain, using the reasoning behind empirical and molecular formulae, why further information (such as the relative molecular mass) would be needed to confirm whether this empirical formula is also the molecular formula of the compound.

   [6 marks]

   Total for question 4: 12 marks

End of questions