Mark Scheme

Section A: 1. B; 2. B; 3. C; 4. C; 5. B; 6. B. (6)

7 (a) measure volume of gas with a gas syringe (1) at regular time intervals / measure mass loss on a balance (1). (b) smaller pieces have a larger surface area (1); more particles exposed/available to collide (1); more frequent collisions → faster (1). (c) a catalyst lowers the activation energy (1); shown as a lower "hump" with reactants/products unchanged (1). (7)

8 (a) CₙH₂ₙ₊₂ (1). (b) add bromine water (1); turns from orange to colourless (1). (c) long-chain hydrocarbons are less useful / lower demand (1); cracking makes smaller, more useful molecules (1); and produces alkenes for polymers (1). (6)

9 (a) methanol; ethanol (2). (b) any two: burns/combusts; reacts with sodium; oxidised to a carboxylic acid; dissolves to a neutral solution (2). (c) they are only partially ionised in water (1); so lower H⁺ concentration / higher pH than strong acids of the same concentration (1). (6)

10 (a) if conditions change, the equilibrium shifts to oppose the change (1). (b) increasing pressure shifts to the side with fewer gas molecules (1); the product (NH₃) side, so yield increases (1). (c) lower temperature gives higher yield but slower rate (1); 450 °C is a compromise for an acceptable rate/yield (1). (5)

11 (a) lithium = crimson/red; sodium = yellow; copper = green (3). (b) add dilute HCl then barium chloride (1); white precipitate (1). (c) any one: faster; more accurate; more sensitive/tiny samples (1). (6)

12 (a) assesses the environmental impact of a product over its whole life (1): raw materials, manufacture, use, disposal (1). (b) saves energy and finite resources / ore compared with extracting new metal (2). (c) plants absorb metal compounds as they grow (1); plants are burned to ash (1); metal extracted from the ash (1). (7)

13 (a) different-sized atoms distort the layers (1); so layers cannot slide easily (1). (b) needs water and oxygen (1); prevent by a barrier (paint/oil) or sacrificial protection (galvanising) (1). (4)

14 (a) nitrogen ≈ 78% (1); oxygen ≈ 21% (1). (b) algae and then plants evolved and photosynthesised (1); photosynthesis releases oxygen (1). (c) any two: carbon dioxide; methane; water vapour (2). (d) any two: sea level rise from melting ice; more extreme/frequent weather; changing species distribution; reduced crop yields (2). (e) the climate system is very complex / many interacting variables / hard to make reliable predictions (1). (9)

15 (a) water that is safe to drink (low levels of dissolved salts and microbes) (1). (b) filter to remove solids (1); sterilise with chlorine/ozone/UV to kill microbes (1). (c) spot the mixture on a pencil baseline (1); place in solvent below the line so the solvent rises and carries the colourings different distances (1); measure distance moved by a spot and by the solvent (1); Rf = distance moved by spot ÷ distance moved by solvent (1). (d) insert a glowing splint (1); it relights (1). (e) it melts at a single, sharp temperature because it contains only one substance (1). (10)

16 — Levels (6): Indicative: Carbonate: add dilute acid → fizzing → bubble the gas through limewater → turns cloudy (CO₂). Chloride: add dilute nitric acid then silver nitrate solution → white precipitate. (Add nitric acid first to remove carbonate.)

• L3 (5–6): Both tests with correct method and correct positive result.
• L2 (3–4): One test fully correct, or both partially.
• L1 (1–2): A single relevant point.

17 — Levels (6): Indicative: raising the temperature gives particles more kinetic energy, so they move faster and collide more frequently; a greater proportion of collisions have energy ≥ the activation energy, so more collisions are successful per second and the rate increases. On a reaction profile, a catalyst provides an alternative pathway with a lower activation energy (a lower "hump"); the reactant and product energy levels are unchanged.

• L3 (5–6): Correct collision-theory explanation and correct reaction-profile description of a catalyst.
• L2 (3–4): Some of the temperature effect and/or the catalyst profile.
• L1 (1–2): Simple statements.

18 — Levels (6): Indicative: ethene is an alkene with a C=C double bond; many ethene monomers join by addition polymerisation when the double bonds open, forming long chains of poly(ethene) with no other product. Disposal problems: most polymers are non-biodegradable so persist in landfill; burning can release toxic gases/CO₂; they harm wildlife. Recycling reduces this but requires sorting.

• L3 (5–6): Correct addition-polymerisation account and valid disposal problems.
• L2 (3–4): Some of the polymerisation or the disposal issues.
• L1 (1–2): Simple statements.

19 — Levels (6): Indicative: increasing pressure shifts equilibrium to the side with fewer gas molecules — the 2NH₃ side (4 molecules → 2) — so yield increases; very high pressure is costly/dangerous. The forward reaction is exothermic, so a lower temperature gives a higher yield, but the rate would be too slow; about 450 °C is a compromise giving an acceptable rate and yield. Le Chatelier's principle: the system shifts to oppose the imposed change.

• L3 (5–6): Correctly applies Le Chatelier to both pressure and temperature with the compromise idea.
• L2 (3–4): One factor fully or both partially.
• L1 (1–2): Simple statements.

20 — Levels (6): Indicative: traditional mining digs up and processes ore, using lots of energy and producing waste/scarring the landscape. Phytomining: plants absorb metal compounds; the plants are burned to ash from which copper is extracted. Bioleaching: bacteria produce leachate solutions containing copper compounds. The newer methods can use low-grade ores, cause less environmental damage and use less energy, but are slow.

• L3 (5–6): Both new methods described and environmental advantages compared with mining.
• L2 (3–4): One method with some comparison.
• L1 (1–2): Simple statements.

21 — Levels (4): Indicative: in flame emission spectroscopy a sample is put into a flame and the light emitted is passed to a spectroscope; each metal ion produces a characteristic line spectrum used to identify it (and concentration from intensity). Advantages over flame tests: more accurate, more sensitive (tiny samples), faster, and can identify ions in mixtures.

• L2 (3–4): Correct outline of the method and at least one clear advantage.
• L1 (1–2): Simple statements.

Sample Answers with Examiner Commentary

Question 16 — Sample Answers

Grade 9 answer "To test for carbonate ions, add a dilute acid to the solution. If carbonate ions are present it will fizz, producing carbon dioxide. Bubble this gas through limewater — it turns cloudy/milky, confirming carbon dioxide and therefore carbonate. To test for chloride ions, add a few drops of dilute nitric acid (to remove any carbonate) followed by silver nitrate solution. A white precipitate (silver chloride) confirms chloride ions." Mark: 6/6. Examiner commentary: Both tests have the correct reagents, methods and positive results, and the candidate sensibly adds nitric acid first in the halide test. Top band.

Grade 6 answer "For carbonate, add acid and it fizzes and makes carbon dioxide which turns limewater cloudy. For chloride, add silver nitrate and you get a white precipitate." Mark: 4/6. Examiner commentary: The carbonate test is complete. The chloride test gives the correct reagent and result but omits adding nitric acid first, which examiners expect; still, most marks are awarded.

Question 10(b) — Sample Answers

Grade 9 answer "Increasing the pressure shifts the equilibrium towards the side with fewer gas molecules. There are 4 molecules of gas on the left (N₂ + 3H₂) and only 2 on the right (2NH₃), so the equilibrium shifts to the right, increasing the yield of ammonia." Mark: 2/2. Examiner commentary: Correctly applies Le Chatelier with the molecule count to justify the higher yield.

Grade 6 answer "Higher pressure makes more ammonia because it pushes the reaction towards the products." Mark: 1/2. Examiner commentary: Correct outcome but no reasoning about fewer gas molecules on the product side, which is the key marking point.