1. 1
   A student burns magnesium ribbon completely in a stream of pure oxygen gas. All of the magnesium is converted into a white solid, magnesium oxide, MgO, with no other products formed.

   (a)

   Which word equation correctly describes this reaction?

   [1 mark]

   • Amagnesium + oxygen → magnesium oxide
   • Bmagnesium oxide → magnesium + oxygen
   • Cmagnesium + oxygen → magnesium hydroxide
   • Dmagnesium + magnesium oxide → oxygen

   (b)

   Which symbol equation, including state symbols, is correctly balanced for this reaction?

   [1 mark]

   • AMg(s) + O2(g) → MgO(s)
   • B2Mg(s) + O2(g) → 2MgO(s)
   • CMg(s) + O(g) → MgO(s)
   • DMg(s) + O2(g) → MgO2(s)

   (c)

   Deduce the formula of magnesium oxide from the fact that one magnesium ion, Mg2+, combines with one oxide ion, O2−, and explain how you obtained your answer.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student is told that the relative atomic masses are H = 1, C = 12, N = 14 and O = 16, and is asked to find the relative molecular mass, Mr, of urea, a compound with the molecular formula CO(NH2)2.

   (a)

   How many atoms of hydrogen are there in one molecule of urea, CO(NH2)2?

   [1 mark]

   • A2
   • B4
   • C6
   • D8

   (b)

   What is the relative molecular mass, Mr, of urea, CO(NH2)2?

   [1 mark]

   • A46
   • B52
   • C60
   • D64

   (c)

   Calculate the relative molecular mass, Mr, of carbon dioxide, CO2, showing your working. (C = 12, O = 16)

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A technician weighs out 8.0 g of solid sodium hydroxide, NaOH, to prepare a stock solution. (Na = 23, O = 16, H = 1)

   (a)

   Calculate the molar mass of sodium hydroxide, NaOH, and use this to calculate the amount, in moles, of sodium hydroxide in the 8.0 g sample.

   [3 marks]

   (b)

   Calculate the number of hydroxide ions, OH−, present in the 8.0 g sample of sodium hydroxide, given that the Avogadro constant is 6.02 × 10^23 per mole, and that each formula unit of NaOH contains one hydroxide ion.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A 4.4 g sample of a pure hydrocarbon is burned completely in excess oxygen. The products are found to contain 7.2 g of water and 13.2 g of carbon dioxide. (C = 12, O = 16, H = 1)

   (a)

   Use the given masses to calculate the empirical formula of the hydrocarbon, showing your working clearly.

   [6 marks]

   (b)

   The hydrocarbon is later confirmed to have a molar mass of 44 g/mol. Determine its molecular formula, and calculate the number of molecules present in a 2.2 g sample of the hydrocarbon, given the Avogadro constant is 6.02 × 10^23 per mole.

   [6 marks]

   Total for question 4: 12 marks

5. 5
   A student reacts dilute hydrochloric acid with an excess of solid calcium carbonate. Carbon dioxide gas, calcium chloride solution and water are formed.

   (a)

   Which word equation correctly represents this reaction?

   [1 mark]

   • Acalcium carbonate + hydrochloric acid → calcium chloride + water + carbon dioxide
   • Bcalcium carbonate + hydrochloric acid → calcium oxide + carbon dioxide
   • Ccalcium chloride + carbon dioxide → calcium carbonate + hydrochloric acid
   • Dcalcium carbonate + water → calcium chloride + hydrochloric acid

   (b)

   Which balanced symbol equation, with state symbols, correctly represents this reaction?

   [1 mark]

   • ACaCO3(s) + HCl(aq) → CaCl2(aq) + H2O(l) + CO2(g)
   • BCaCO3(s) + 2HCl(aq) → CaCl2(aq) + H2O(l) + CO2(g)
   • CCaCO3(s) + 2HCl(aq) → CaCl(aq) + H2O(l) + CO2(g)
   • DCa(s) + 2HCl(aq) → CaCl2(aq) + H2(g)

   (c)

   Deduce the formula of calcium chloride from the fact that a calcium ion, Ca2+, combines with chloride ions, Cl−, and explain how you obtained your answer.

   [2 marks]

   Total for question 5: 4 marks

6. 6
   A student calculates the relative formula mass of ammonium sulfate, (NH4)2SO4, a compound used as a fertiliser. (N = 14, H = 1, S = 32, O = 16)

   (a)

   How many hydrogen atoms are there in one formula unit of ammonium sulfate, (NH4)2SO4?

   [1 mark]

   • A4
   • B6
   • C8
   • D10

   (b)

   What is the relative formula mass, Mr, of ammonium sulfate, (NH4)2SO4?

   [1 mark]

   • A96
   • B116
   • C124
   • D132

   (c)

   Calculate the percentage by mass of nitrogen in ammonium sulfate, (NH4)2SO4, showing your working. (N = 14, Mr of (NH4)2SO4 = 132)

   [2 marks]

   Total for question 6: 4 marks

7. 7
   A student reacts an excess of magnesium ribbon with 50 cm3 of dilute hydrochloric acid of concentration 2.0 mol/dm3, producing hydrogen gas. (Molar gas volume at r.t.p. = 24 dm3/mol)

   (a)

   Calculate the amount, in moles, of hydrochloric acid used, and use the equation Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g) to calculate the amount, in moles, of hydrogen gas produced.

   [3 marks]

   (b)

   Calculate the volume, in cm3, of hydrogen gas produced at room temperature and pressure, and state the total volume of gas that would be produced if the same experiment were repeated using 100 cm3 of the same 2.0 mol/dm3 hydrochloric acid, with magnesium still in excess.

   [4 marks]

   Total for question 7: 7 marks

8. 8
   In an industrial process, 20.0 g of impure calcium carbonate is heated strongly to decompose it, producing calcium oxide and carbon dioxide gas: CaCO3(s) → CaO(s) + CO2(g). (Ca = 40, C = 12, O = 16)

   (a)

   Calculate the maximum theoretical mass of calcium oxide that could be produced from 20.0 g of pure calcium carbonate, and then calculate the percentage yield if only 9.52 g of calcium oxide was actually obtained from the 20.0 g impure sample.

   [6 marks]

   (b)

   The 20.0 g sample used was impure, containing some sand that does not decompose on heating. Given that pure calcium carbonate would have produced 11.2 g of calcium oxide, but only 9.52 g was actually obtained even though the reaction went to completion with no losses, calculate the percentage purity of the original 20.0 g sample of calcium carbonate, showing your reasoning.

   [6 marks]

   Total for question 8: 12 marks

End of questions