Total marks: 90 · Duration: 105 minutes · Tier: Higher
Instructions to candidates
- Use black ink. You may use an HB pencil for graphs and diagrams.
- Answer all the questions.
- In calculations, show your working and give the unit of your answer.
- You may use a scientific or graphical calculator.
- Section A: for each question, choose one answer, A, B, C or D.
- Where a question describes apparatus in words, you may find it helpful to sketch it.
Information
- The total mark for this paper is 90. Section A is worth 15 marks and Section B is worth 75 marks.
- The marks for each question are shown in brackets.
- Quality of extended response will be assessed in questions marked with an asterisk (*).
- This paper covers OCR GCSE (9–1) Gateway Chemistry A Higher Paper 1 content, topics C1 to C3: particles; elements, compounds and mixtures; and chemical reactions.
- Relative atomic masses (Ar): H = 1, C = 12, N = 14, O = 16, Na = 23, Mg = 24, Cl = 35.5, Ca = 40, Fe = 56. The Avogadro constant is 6.02 × 10²³ per mole.
Paper
Section A — Multiple choice (15 marks)
1. Which is a limitation of the simple particle model, in which particles are drawn as solid spheres? [1 mark]
A it shows that particles are close together in a solid B it shows that particles in a gas are far apart C it shows the arrangement of particles in a liquid D it does not show the forces between the particles
2. What do the isotopes of an element have in common? [1 mark]
A the same mass number B the same number of protons C the same number of neutrons D the same relative mass
3. Which subatomic particle was discovered by James Chadwick? [1 mark]
A neutron B proton C electron D nucleus
4. In a chromatography experiment, a spot moves 3.0 cm and the solvent front moves 7.5 cm. What is the Rf value of the spot? [1 mark]
A 2.5 B 4.5 C 0.40 D 0.25
5. Which method is best for separating ethanol from a mixture of ethanol and water? [1 mark]
A filtration B fractional distillation C crystallisation D chromatography
6. Magnesium forms Mg²⁺ ions and nitrogen forms N³⁻ ions. What is the formula of magnesium nitride? [1 mark]
A MgN B Mg₂N₃ C MgN₂ D Mg₃N₂
7. Which substance has a giant covalent structure? [1 mark]
A silicon dioxide B carbon dioxide C sodium chloride D methane
8. What is the typical size range of a nanoparticle? [1 mark]
A 0.1 to 1 nm B 100 to 2500 nm C 1 to 100 nm D 1 to 10 μm
9. What is the relative formula mass of calcium nitrate, Ca(NO₃)₂? [1 mark]
A 102 B 164 C 150 D 204
10. How many moles are there in 8.8 g of carbon dioxide, CO₂? [1 mark]
A 0.20 mol B 0.80 mol C 5.0 mol D 0.10 mol
11. Which reaction is endothermic? [1 mark]
A combustion of methane B neutralisation of an acid by an alkali C respiration D thermal decomposition of calcium carbonate
12. Which half equation shows the reaction at the cathode when molten sodium chloride is electrolysed? [1 mark]
A 2Cl⁻ → Cl₂ + 2e⁻ B Na → Na⁺ + e⁻ C Na⁺ + e⁻ → Na D Cl₂ + 2e⁻ → 2Cl⁻
13. What is the most likely pH of dilute ethanoic acid? [1 mark]
A 1 B 4 C 7 D 10
14. Which ion is present in all acidic solutions? [1 mark]
A H⁺ B OH⁻ C Cl⁻ D Na⁺
15. What is oxidation, in terms of electrons? [1 mark]
A gain of electrons B gain of protons C loss of electrons D sharing of electrons
Section B (75 marks)
Question 16 — Atomic structure and the periodic table (8 marks)
(a) Give the electronic structure of a silicon atom (atomic number 14). [1 mark]
(b) Chlorine has two isotopes, chlorine-35 and chlorine-37. Its atomic number is 17. Give the number of neutrons in each isotope. [1 mark]
(c) Boron has two isotopes: 19.9% boron-10 and 80.1% boron-11. Calculate the relative atomic mass of boron. Give your answer to 1 decimal place. [2 marks]
(d) Describe how Mendeleev arranged the elements in his periodic table, and explain why the discovery of gallium and germanium led scientists to accept his table. [3 marks]
(e) Explain why sodium and potassium have similar chemical reactions. [1 mark]
Question 17 — Bonding and properties (12 marks)
(a) Magnesium reacts with chlorine to form magnesium chloride, MgCl₂. Describe, in terms of electrons, how magnesium chloride is formed. [3 marks]
(b) Explain why magnesium chloride has a high melting point. [2 marks]
(c) Explain why chlorine, Cl₂, is a gas at room temperature. [2 marks]
(d) Explain why graphite is soft and slippery, so that it can be used as a lubricant. [2 marks]
(e) Silver nanoparticles are added to socks to kill bacteria.
(i) A silver nanoparticle is a cube with sides of 20 nm. Calculate its surface area to volume ratio. [2 marks]
(ii) Give one possible risk of using nanoparticles in clothing. [1 mark]
Question 18 — Purifying substances (10 marks)
(a) Rock salt is a mixture of salt (sodium chloride) and sand. Describe how a student could obtain pure, dry crystals of salt from rock salt. [4 marks]
(b) Paint is a formulation. Explain what this means. [1 mark]
(c) Explain how paper chromatography separates the substances in a mixture. [2 marks]
(d) Pure benzoic acid melts at 122 °C. A student's sample of benzoic acid melts between 118 °C and 121 °C. Is the student's sample pure? Explain your answer. [2 marks]
(e) Name the method used to obtain pure water from sea water in the laboratory. [1 mark]
Question 19 — Quantitative chemistry (13 marks)
(a) Balance the equation for the reduction of iron(III) oxide by carbon monoxide:
___ Fe₂O₃ + ___ CO → ___ Fe + ___ CO₂ [1 mark]
(b) Calculate the maximum mass of iron that can be made from 32.0 g of iron(III) oxide. [3 marks]
(c) Sodium reacts with chlorine: 2Na + Cl₂ → 2NaCl
A student reacts 4.6 g of sodium with 4.26 g of chlorine.
(i) Show that chlorine is the limiting reactant. [3 marks]
(ii) Calculate the maximum mass of sodium chloride formed. [2 marks]
(d) Calculate the number of oxygen atoms in 0.50 mol of oxygen gas, O₂. [2 marks]
(e) A student dissolves 3.65 g of hydrogen chloride in water and makes the solution up to 500 cm³. Calculate the concentration in g/dm³. [2 marks]
Question 20 — Energy changes (8 marks)
(a) Describe what a reaction profile shows for an exothermic reaction. Include the activation energy in your answer. [2 marks]
(b) Ammonia is made from nitrogen and hydrogen:
N₂ + 3H₂ → 2NH₃
| Bond | Bond energy (kJ/mol) |
|---|---|
| N≡N | 945 |
| H–H | 436 |
| N–H | 391 |
Calculate the energy change for this reaction. [3 marks]
(c) A student dissolves ammonium nitrate in water. The temperature of the water falls from 21.0 °C to 15.5 °C.
(i) Calculate the temperature change. [1 mark]
(ii) Give one everyday use of a reaction like this. [1 mark]
(d) Explain, in terms of bonds, why some reactions are endothermic. [1 mark]
Question 21 — Acids and redox (12 marks)
(a)* A student has two acid solutions of the same concentration: hydrochloric acid and ethanoic acid.
Describe experiments the student could do to show that hydrochloric acid is a strong acid and ethanoic acid is a weak acid. Explain the expected results in terms of ionisation. [6 marks]
(b) Iron(III) ions react with copper:
2Fe³⁺ + Cu → 2Fe²⁺ + Cu²⁺
Identify the species that is reduced. Explain your answer in terms of electrons. [2 marks]
(c) Write a balanced equation for the reaction between sulfuric acid, H₂SO₄, and potassium carbonate, K₂CO₃. [2 marks]
(d) The pH of a solution changes from 3 to 6. By what factor has the hydrogen ion concentration changed? [1 mark]
(e) Name the salt formed when nitric acid reacts with calcium oxide. [1 mark]
Question 22 — Electrolysis (12 marks)
(a) Copper chloride solution is electrolysed using inert electrodes. Name the product at each electrode. [2 marks]
(b) Write the half equation for the reaction at
(i) the cathode [1 mark]
(ii) the anode. [1 mark]
(c) Potassium sulfate solution is electrolysed using inert electrodes.
(i) Name the product at each electrode. [2 marks]
(ii) Explain why potassium is not formed at the cathode. [1 mark]
(iii) Write the half equation for the formation of oxygen from hydroxide ions. [1 mark]
(d) Copper is purified by electrolysis using an impure copper anode and a pure copper cathode in copper sulfate solution.
(i) Explain why the anode loses mass and the cathode gains mass. [2 marks]
(ii) What happens to the impurities in the anode? [1 mark]
(e) Explain why an ionic compound must be molten or dissolved in water before it can be electrolysed. [1 mark]