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 — 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.

Sample Answers with Examiner Commentary

Question 14 — 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.