Total marks: 100 · Duration: 105 minutes · Tier: Higher
Instructions to candidates
- Use black ink or black ball-point pen. Draw diagrams in pencil.
- Answer all questions in the spaces provided.
- In all calculations, show clearly how you work out your answer.
- You may use a calculator.
- Where a question describes apparatus or a diagram in words, you may find it helpful to sketch it.
Information
- The maximum mark for this paper is 100.
- The marks for questions are shown in brackets.
- You are expected to use good English and to organise information clearly, especially in questions marked with an asterisk (*).
- This paper covers AQA GCSE Chemistry topics 4.1 to 4.5: atomic structure and the periodic table; bonding, structure and the properties of matter; quantitative chemistry; chemical changes; and energy changes.
- Relative atomic masses (Ar): H = 1, C = 12, O = 16, Mg = 24, Al = 27, Cl = 35.5, Ca = 40. One mole of any gas occupies 24 dm³ at room temperature and pressure.
Paper
Question 1 — Atomic structure (10 marks)
(a) In the plum pudding model, the atom was a ball of positive charge with electrons embedded in it. In the alpha particle scattering experiment, alpha particles were fired at a thin sheet of gold foil.
Describe what was observed and explain how each observation led to the nuclear model of the atom. [3 marks]
(b) James Chadwick's work added a new particle to the nuclear model. Name this particle. [1 mark]
(c) Chlorine has two isotopes. 75% of chlorine atoms are chlorine-35 and 25% are chlorine-37.
Show that the relative atomic mass of chlorine is 35.5. [2 marks]
(d) A potassium ion is written as ³⁹₁₉K⁺. Give the number of protons, neutrons and electrons in this ion. [3 marks]
(e) Give the electronic structure of a sulfur atom (atomic number 16). [1 mark]
Question 2 — The periodic table (11 marks)
(a) Explain why the reactivity of the Group 1 metals increases going down the group. [3 marks]
(b) Write a balanced equation for the reaction of potassium with water. [2 marks]
(c) A student adds chlorine water to a colourless solution of potassium bromide.
(i) State what the student would observe. [1 mark]
(ii) Write the ionic equation for the reaction. [2 marks]
(iii) Explain, in terms of electrons, why chlorine is more reactive than bromine. [2 marks]
(d) Give one way in which the transition metals differ from the Group 1 metals. [1 mark]
Question 3 — Bonding and structure (12 marks)
(a) Magnesium reacts with oxygen to form magnesium oxide, an ionic compound.
Describe, in terms of electrons, what happens when magnesium oxide is formed. [3 marks]
(b) Explain why magnesium oxide has a high melting point. [2 marks]
(c) Diamond and graphite are both forms of carbon. Explain why graphite conducts electricity but diamond does not. [3 marks]
(d) Explain why methane, CH₄, has a low boiling point. [2 marks]
(e) A nanoparticle is a cube of side 10 nm. A fine particle is a cube of side 100 nm.
How many times larger is the surface area to volume ratio of the nanoparticle than that of the fine particle? [2 marks]
Question 4 — Quantitative chemistry (14 marks)
(a) Calculate the relative formula mass (Mr) of calcium hydroxide, Ca(OH)₂. [1 mark]
(b) Magnesium burns in oxygen: 2Mg + O₂ → 2MgO
Calculate the mass of magnesium oxide formed when 6.0 g of magnesium burns completely. [3 marks]
(c) A student heats magnesium ribbon in an open crucible. The mass of the crucible and its contents increases.
Explain why the mass increases, even though mass is conserved in chemical reactions. [2 marks]
(d) In a titration, 25.0 cm³ of sodium hydroxide solution is neutralised by 20.0 cm³ of 0.150 mol/dm³ sulfuric acid.
2NaOH + H₂SO₄ → Na₂SO₄ + 2H₂O
Calculate the concentration of the sodium hydroxide solution in mol/dm³. [4 marks]
(e) Calculate the volume of 0.88 g of carbon dioxide, CO₂, at room temperature and pressure. [2 marks]
(f) Hydrogen can be made from methane: CH₄ + H₂O → CO + 3H₂
Calculate the percentage atom economy for making hydrogen by this reaction. Give your answer to 3 significant figures. [2 marks]
Question 5 — Chemical changes (15 marks)
(a)* Copper sulfate crystals can be made from insoluble copper(II) oxide and dilute sulfuric acid.
Describe a method to make pure, dry crystals of copper sulfate. [6 marks]
(b) A solution of copper(II) chloride is electrolysed using inert electrodes.
(i) Name the product at each electrode. [2 marks]
(ii) Write a half equation for the reaction at the positive electrode. [1 mark]
(c) (i) Explain the difference between a strong acid and a concentrated acid. [2 marks]
(ii) The pH of an acid solution changes from 4 to 2. By what factor does the concentration of hydrogen ions change? [1 mark]
(d) Iron is extracted from iron(III) oxide by heating it with carbon: 2Fe₂O₃ + 3C → 4Fe + 3CO₂
Identify the substance that is reduced in this reaction. Give a reason for your answer. [2 marks]
(e) Write the ionic equation for a neutralisation reaction between an acid and an alkali. [1 mark]
Question 6 — Energy changes (12 marks)
(a) Hydrogen reacts with chlorine: H–H + Cl–Cl → 2 H–Cl
| Bond | Bond energy (kJ/mol) |
|---|---|
| H–H | 436 |
| Cl–Cl | 243 |
| H–Cl | 432 |
(i) Calculate the overall energy change for this reaction. [3 marks]
(ii) State whether the reaction is exothermic or endothermic. Give a reason. [1 mark]
(b) A student investigates the temperature change when different volumes of dilute hydrochloric acid are added to 25 cm³ of sodium hydroxide solution in a polystyrene cup.
(i) Identify the independent variable. [1 mark]
(ii) Give one way to reduce energy transfer to the surroundings. [1 mark]
(iii) The temperature rises as acid is added, up to 20 cm³ of acid. Adding more acid after this makes the temperature fall. Explain why. [2 marks]
(c) (i) What is meant by the activation energy of a reaction? [1 mark]
(ii) State the effect of a catalyst on the activation energy. [1 mark]
(d) A hydrogen fuel cell powers an electric bus.
(i) Name the only product of the overall reaction in a hydrogen fuel cell. [1 mark]
(ii) Give one advantage of hydrogen fuel cells compared with rechargeable batteries. [1 mark]
Question 7 — Electrolysis of aluminium oxide (10 marks)
Aluminium is extracted by the electrolysis of aluminium oxide, Al₂O₃, dissolved in molten cryolite. The positive electrodes are made of carbon.
(a) Explain why the aluminium oxide is dissolved in molten cryolite. [1 mark]
(b) Explain why the positive electrodes must be replaced regularly. [2 marks]
(c) Write a half equation for the reaction at
(i) the negative electrode [1 mark]
(ii) the positive electrode. [1 mark]
(d) Calculate the maximum mass of aluminium that can be produced from 102 kg of aluminium oxide. [3 marks]
(e) Explain why aluminium is extracted by electrolysis and not by heating its oxide with carbon. [1 mark]
(f) Suggest why aluminium plants are often built near hydroelectric power stations. [1 mark]
Question 8 — Structure and properties (8 marks)
(a)* The table gives information about three substances.
| Substance | Melting point | Conducts electricity? |
|---|---|---|
| Sodium chloride | 801 °C | Only when molten or dissolved in water |
| Diamond | Above 3500 °C | No |
| Poly(ethene) | Softens at about 120 °C | No |
Explain these properties in terms of the structure and bonding of each substance. [6 marks]
(b) A student dissolves 14.6 g of sodium chloride in water and makes the solution up to 250 cm³.
Calculate the concentration of the solution in g/dm³. [2 marks]
Question 9 — Reacting quantities (8 marks)
A student adds 1.2 g of magnesium ribbon to 50 cm³ of 1.0 mol/dm³ hydrochloric acid.
Mg + 2HCl → MgCl₂ + H₂
(a) Show that the hydrochloric acid is the limiting reactant. [3 marks]
(b) Calculate the maximum volume of hydrogen, in dm³, that can be produced at room temperature and pressure. [2 marks]
(c) The student collects 0.54 dm³ of hydrogen. Calculate the percentage yield. [2 marks]
(d) Give one reason why the yield is less than 100%. [1 mark]