OCR GCSE Chemistry — Paper 1 (Higher Tier)
Total marks: 90 · Duration: 105 minutes · Tier: Higher
Instructions to candidates
• Answer ALL questions in both Section A and Section B. • Write your answers in black ink or black ball-point pen in the spaces provided on the question paper. • You may use an HB pencil for graphs and diagrams. • A calculator may be used throughout this paper. • The marks for each question are shown in brackets [ ]. Use this as a guide as to how much time to spend on each question. • The total number of marks available is 90. • Write your answers clearly and in good English. You will be assessed on the quality of your written communication in Section B. • The Periodic Table is provided on page 2.
Paper
Section A — Structured Questions (54 marks)
1. A student investigated the reactivity of three metals with dilute hydrochloric acid.
The student added 2.0 g of each metal to separate test tubes containing 25 cm³ of 1.0 mol/dm³ hydrochloric acid at 20°C.
Table 1 shows the results.
| Metal | Observations | Time for reaction to complete (s) |
|---|---|---|
| Magnesium | Vigorous fizzing, metal disappears | 45 |
| Zinc | Steady fizzing, metal disappears | 320 |
| Iron | Very slow fizzing, some metal remains | Reaction incomplete after 600 |
(a) The equation for the reaction between magnesium and hydrochloric acid is:
Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g)
State how you could test for the gas produced in this reaction.
(2 marks)
(b) Explain, in terms of electrons, what happens to magnesium atoms during this reaction.
(2 marks)
(c) The student concluded that magnesium is more reactive than zinc.
Explain how the results in Table 1 support this conclusion.
(2 marks)
(d) Suggest why some iron remained unreacted after 600 seconds.
(1 mark)
(e) The student repeated the experiment with magnesium using hydrochloric acid at 40°C.
Predict how this would affect the time taken for the reaction to complete.
Explain your answer in terms of particles.
(3 marks)
2. Crude oil is a mixture of hydrocarbons that can be separated by fractional distillation.
Figure 1 shows a simplified fractional distillation column.
[Figure 1: A vertical column showing four labeled fractions being removed at different heights. From top to bottom: "Gases (withdrawn at top, temperature approximately 25°C)", "Petrol (withdrawn at 110°C)", "Diesel oil (withdrawn at 250°C)", and "Bitumen (withdrawn at bottom, temperature approximately 350°C)". An arrow labeled "Crude oil vapour enters" points to the bottom of the column.]
(a) Explain why different fractions are removed at different levels in the column.
(3 marks)
(b) Petrol contains hydrocarbons with the general formula CₙH₂ₙ₊₂.
(i) State the name of this homologous series.
(1 mark)
(ii) A hydrocarbon in petrol has the molecular formula C₈H₁₈.
Calculate the relative formula mass (Mᵣ) of C₈H₁₈.
(Relative atomic masses: H = 1, C = 12)
(2 marks)
(c) Large hydrocarbon molecules from the bitumen fraction can be broken down into smaller, more useful molecules by cracking.
One possible cracking reaction is:
C₁₆H₃₄ → C₈H₁₈ + C₃H₆ + X
(i) Determine the molecular formula of the product X.
(2 marks)
(ii) State one condition needed for cracking to occur.
(1 mark)
(d) Propene (C₃H₆) is an unsaturated hydrocarbon.
Describe a chemical test you could use to show that propene is unsaturated.
Include what you would observe.
(3 marks)
3. A student investigated the electrolysis of copper sulfate solution using carbon electrodes.
The student used the circuit shown in Figure 2.
[Figure 2: A diagram showing a beaker containing copper sulfate solution with two carbon electrodes connected to a battery. The positive electrode (anode) is on the right and the negative electrode (cathode) is on the left. Wires connect the electrodes to a battery and variable resistor.]
(a) State what happens to copper ions (Cu²⁺) during electrolysis.
(1 mark)
(b) Complete the half equation for the reaction at the negative electrode (cathode).
Cu²⁺ + _______ → Cu
(1 mark)
(c) The student observed that bubbles of gas were produced at the positive electrode (anode).
(i) Identify the gas produced at the anode.
(1 mark)
(ii) Explain why this gas is produced at the anode instead of copper.
(2 marks)
(d) The student measured the mass of the cathode before and after electrolysis.
Table 2 shows the results.
| Mass of cathode before electrolysis (g) | Mass of cathode after electrolysis (g) |
|---|---|
| 12.45 | 12.77 |
Calculate the mass of copper deposited on the cathode.
(1 mark)
(e) The student repeated the experiment using copper electrodes instead of carbon electrodes.
Describe what would happen at each electrode during electrolysis with copper electrodes.
(3 marks)
4. Ammonia (NH₃) is manufactured by the Haber process.
The equation for the reaction is:
N₂(g) + 3H₂(g) ⇌ 2NH₃(g) ΔH = -92 kJ/mol
The forward reaction is exothermic.
(a) State the meaning of the symbol ⇌ in the equation.
(1 mark)
(b) The Haber process is carried out at a temperature of 450°C and a pressure of 200 atmospheres, using an iron catalyst.
(i) Explain why a high pressure is used in terms of the position of equilibrium.
(2 marks)
(ii) Explain why a temperature of 450°C is used rather than a lower temperature, even though a lower temperature would give a higher yield of ammonia.
(2 marks)
(iii) State the effect of using an iron catalyst on the position of equilibrium.
(1 mark)
(c) A chemist investigated the effect of temperature on the yield of ammonia at equilibrium.
Table 3 shows the results at a constant pressure of 200 atmospheres.
| Temperature (°C) | Percentage yield of ammonia at equilibrium (%) |
|---|---|
| 350 | 45 |
| 450 | 25 |
| 550 | 15 |
Explain the trend shown in Table 3.
(3 marks)
(d) Calculate the atom economy for the production of ammonia in the Haber process.
(Relative atomic masses: H = 1, N = 14)
(3 marks)
5. The Periodic Table shows the elements arranged in order of atomic number.
Figure 3 shows part of the Periodic Table.
[Figure 3: A partial periodic table showing Groups 1, 2, and 7. Group 1 shows Li (lithium, 3), Na (sodium, 11), and K (potassium, 19). Group 2 shows Be (beryllium, 4), Mg (magnesium, 12), and Ca (calcium, 20). Group 7 shows F (fluorine, 9), Cl (chlorine, 17), and Br (bromine, 35).]
(a) State what is meant by the term 'atomic number'.
(1 mark)
(b) An atom of sodium has an atomic number of 11 and a mass number of 23.
Describe the structure of this sodium atom in terms of the numbers of protons, neutrons, and electrons.
(3 marks)
(c) Elements in Group 1 are called alkali metals.
(i) Describe the trend in reactivity as you go down Group 1.
(1 mark)
(ii) Explain this trend in reactivity in terms of electronic structure.
(3 marks)
(d) Sodium reacts with chlorine to form sodium chloride.
(i) Describe, in terms of electrons, what happens when a sodium atom reacts with a chlorine atom.
(3 marks)
(ii) Sodium chloride has a high melting point of 801°C.
Explain why sodium chloride has a high melting point.
(3 marks)
6. A student investigated the rate of reaction between marble chips (calcium carbonate) and hydrochloric acid.
The equation for the reaction is:
CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g)
The student measured the volume of carbon dioxide gas produced every 30 seconds.
Figure 4 shows the results.
[Figure 4: A graph with "Time (s)" on the x-axis (0 to 240) and "Volume of CO₂ produced (cm³)" on the y-axis (0 to 100). The curve starts at the origin, rises steeply initially, then gradually levels off to a plateau at approximately 90 cm³ after about 180 seconds.]
(a) Calculate the mean rate of reaction between 0 and 60 seconds.
Give your answer in cm³/s.
(2 marks)
(b) Explain why the rate of reaction decreases over time.
(2 marks)
(c) The student repeated the experiment using the same mass of powdered calcium carbonate instead of marble chips.
All other conditions remained the same.
(i) On Figure 4, sketch the curve you would expect for this experiment.
(2 marks)
(ii) Explain why using powdered calcium carbonate affects the rate of reaction.
(3 marks)
Section B — Extended Response (36 marks)
7. A company manufactures sodium hydroxide by the electrolysis of concentrated sodium chloride solution (brine) in a diaphragm cell.
During electrolysis:
- Hydrogen gas is produced at the negative electrode (cathode)
- Chlorine gas is produced at the positive electrode (anode)
- Sodium hydroxide solution forms in the electrolyte
The ionic half equations for the reactions at the electrodes are:
At the cathode: 2H⁺ + 2e⁻ → H₂
At the anode: 2Cl⁻ → Cl₂ + 2e⁻
Sodium hydroxide, chlorine, and hydrogen are all important industrial chemicals with many uses.
The diaphragm prevents the chlorine gas produced at the anode from mixing with the sodium hydroxide solution and hydrogen gas produced at the cathode. If chlorine and sodium hydroxide mix, they react together.
Evaluate the use of electrolysis to manufacture sodium hydroxide, chlorine, and hydrogen from brine.
In your answer you should:
- explain how electrolysis produces these three useful products
- discuss the economic and environmental considerations of this process
- assess the importance of preventing chlorine from mixing with the other products.
(12 marks)
8. The Earth's atmosphere has changed significantly over the past 4.5 billion years.
Table 4 shows the approximate composition of the Earth's atmosphere today and estimates of the atmosphere composition billions of years ago.
| Gas | Percentage in early atmosphere (4 billion years ago) | Percentage in atmosphere today |
|---|---|---|
| Nitrogen | 5 | 78 |
| Oxygen | 0 | 21 |
| Carbon dioxide | 95 | 0.04 |
| Water vapour | Variable (large amounts) | Variable (trace amounts) |
Scientists believe that the early atmosphere contained large amounts of carbon dioxide and water vapour. There was little or no oxygen.
Oxygen levels increased about 2.7 billion years ago when photosynthetic organisms evolved.
Carbon dioxide levels decreased due to:
- dissolution in the oceans
- formation of sedimentary rocks containing carbonates
- formation of fossil fuels
- use by photosynthetic organisms
Today, human activities are increasing the percentage of carbon dioxide in the atmosphere. The burning of fossil fuels releases carbon dioxide. Deforestation reduces the number of trees that absorb carbon dioxide during photosynthesis.
Increased carbon dioxide levels are linked to climate change.
To what extent have changes in the Earth's atmosphere been beneficial for life on Earth?
In your answer you should:
- explain how the atmosphere has changed over billions of years
- discuss the role of living organisms in changing the atmosphere
- evaluate the consequences of both past and present changes in atmospheric composition.
(12 marks)
9. A research team is developing new alloys for use in aircraft manufacture.
Pure metals have limitations. For example, pure aluminium is too soft for use in aircraft bodies, even though it has a low density.
Alloys are mixtures of metals with other elements. The different-sized atoms in alloys distort the regular arrangement of metal atoms, making it more difficult for layers of atoms to slide over each other. This makes alloys harder than pure metals.
Table 5 shows data for aluminium and two aluminium alloys.
| Material | Density (g/cm³) | Tensile strength (MPa) | Cost per kg (£) |
|---|---|---|---|
| Pure aluminium | 2.70 | 90 | 1.50 |
| Alloy A (aluminium + 4% copper + 1% magnesium) | 2.78 | 450 | 2.80 |
| Alloy B (aluminium + 5% magnesium + 3% zinc) | 2.76 | 380 | 2.40 |
Tensile strength is a measure of how much force a material can withstand before breaking. A higher tensile strength means the material is stronger.
The research team must select an alloy for manufacturing a new aircraft component. The component must be:
- as light as possible
- strong enough to withstand forces during flight
- cost-effective to produce in large quantities
Assess which alloy would be most suitable for manufacturing the aircraft component.
Use data from Table 5 to support your answer.
(12 marks)