2023 AQA GCSE Chemistry 8462 Practice Paper with Answers

a) Protons are equal to the atomic number, which is 3. Electrons in a neutral atom equal the number of protons, which is 3. Neutrons are calculated as mass number minus atomic number: \(7 - 3 = 4\). b) i) Atoms of the same element with different mass numbers (different numbers of neutrons) are called isotopes. ii) Protons have a positive charge (+1) and electrons have a negative charge (-1). Because there are equal numbers of protons and electrons (3 of each), the total charge is zero. c) Lithium has 3 electrons in total. The first shell can hold up to 2 electrons, and the remaining 1 electron goes into the second shell. The electronic structure is 2,1. d) Group 1 metals lose their 1 outer electron to achieve a stable full outer shell, forming an ion with a +1 charge (\(\text{Li}^+\)).

a) 3 marks: 1 mark for 3 protons, 1 mark for 4 neutrons, 1 mark for 3 electrons. b) i) 1 mark for 'isotope(s)'. ii) 2 marks: 1 mark for stating protons are positive and electrons are negative, and 1 mark for stating that because the numbers of protons and electrons are equal, the charges cancel out. c) 2 marks: 1 mark for showing 2 electrons in the inner shell, 1 mark for showing 1 electron in the outer shell (or writing '2,1'). d) 1 mark for '+1' or '\(1^+\)'.

a) Sodium chloride consists of a giant ionic lattice. There are strong electrostatic forces of attraction acting in all directions between oppositely charged sodium (\(\text{Na}^+\)) and chloride (\(\text{Cl}^-\)) ions. A large amount of thermal energy is needed to overcome these strong ionic bonds, leading to a high melting point. b) Water is composed of simple covalent molecules. Although the covalent bonds within each water molecule are very strong, the forces of attraction between different water molecules (intermolecular forces) are weak. Only a small amount of thermal energy is required to overcome these weak intermolecular forces, resulting in a low boiling point. c) For a substance to conduct electricity, it must contain charged particles that are free to move. In solid sodium chloride, the ions are held tightly in fixed positions in the lattice structure and cannot move. When molten or dissolved in water, the ionic bonds are broken, allowing the ions to move freely and carry electrical current.

a) 4 marks: 1 mark for 'giant ionic lattice' or 'giant structure'. 1 mark for mentioning electrostatic forces of attraction between oppositely charged ions. 1 mark for stating these forces/bonds are strong. 1 mark for stating a large amount of energy is required to break/overcome these bonds. b) 2 marks: 1 mark for identifying weak intermolecular forces (between molecules). 1 mark for stating that little energy is needed to overcome these forces (do not accept 'breaking covalent bonds'). c) 3 marks: 1 mark for stating that in solid sodium chloride, the ions are in fixed positions / cannot move. 1 mark for stating that in molten or dissolved sodium chloride, the ions are free to move. 1 mark for stating that these free-moving ions carry the electrical charge.

a) Magnesium is more reactive than copper, so it displaces copper from copper sulfate to produce magnesium sulfate and copper metal. b) The blue color of the copper sulfate solution fades and eventually becomes colorless as magnesium sulfate forms. A reddish-brown or brown solid (copper metal) deposits on the surface of the magnesium. The reaction is exothermic, so the temperature of the mixture increases. c) Based on the reactivity series of metals, magnesium is the most reactive, followed by zinc, then iron, and copper is the least reactive. d) Magnesium atoms (\(\text{Mg}\)) lose two electrons to form magnesium ions (\(\text{Mg}^{2+}\)), which is oxidation: \(\text{Mg} \rightarrow \text{Mg}^{2+} + 2\text{e}^-\). Copper ions (\(\text{Cu}^{2+}\)) gain those two electrons to form copper atoms (\(\text{Cu}\)), which is reduction: \(\text{Cu}^{2+} + 2\text{e}^- \rightarrow \text{Cu}\). Because both oxidation (loss of electrons) and reduction (gain of electrons) take place simultaneously, it is a redox reaction.

a) 2 marks: 1 mark for 'magnesium sulfate' and 1 mark for 'copper' (either order). b) 2 marks: any two observations from: blue solution fades / turns colorless, brown/red-brown solid forms, temperature increases / mixture gets hot. c) 2 marks: 'magnesium, zinc, iron, copper' in this exact order (1 mark if only one metal is out of position, or if the order is completely reversed). d) 3 marks: 1 mark for stating magnesium loses electrons (oxidation). 1 mark for stating copper ions gain electrons (reduction). 1 mark for stating that a redox reaction involves both oxidation and reduction occurring together.

a) i) Copper ions (\(\text{Cu}^{2+}\)) are positive (cations) and migrate to the negative electrode (cathode) where they are reduced to form copper metal. ii) Chloride ions (\(\text{Cl}^-\)) are negative (anions) and migrate to the positive electrode (anode) where they are oxidized to form chlorine gas. b) At the cathode, you will observe a pink or reddish-brown solid coating the electrode. At the anode, you will see bubbles of gas being produced. c) Chlorine gas is acidic and a strong bleaching agent. It will turn damp blue litmus paper red, and then bleach it completely white. d) Solid copper chloride has a giant ionic lattice where ions are locked in fixed positions by strong ionic bonds and cannot move. When copper chloride is dissolved in water to make an aqueous solution, the lattice is broken, and the ions are free to move throughout the solution, allowing them to carry electrical charge.

a) i) 1 mark for 'copper'. ii) 1 mark for 'chlorine' (do not accept 'chloride'). b) 2 marks: 1 mark for stating a pink/brown/red-brown solid forms on the cathode, 1 mark for stating bubbles/fizzing/effervescence is seen at the anode. c) 2 marks: 1 mark for stating the damp blue litmus paper turns red and then bleaches white (or just bleaches white), 1 mark for identifying the gas as chlorine. d) 3 marks: 1 mark for stating that ions are in fixed positions / cannot move in the solid. 1 mark for stating that ions are free to move in the aqueous solution. 1 mark for stating that these moving ions carry the electrical charge/current.

a) In this neutralization reaction, copper oxide (a base) reacts with sulfuric acid to form copper sulfate (the salt) and water: copper oxide + sulfuric acid -> copper sulfate + water. b) i) Excess copper oxide is added to ensure that all of the sulfuric acid is completely neutralized and used up, so the resulting salt solution is not acidic. ii) Copper oxide is an insoluble black powder. When it is in excess, it will no longer react or dissolve in the acid, and a black solid will remain visible at the bottom of the beaker after stirring. iii) The excess insoluble copper oxide is separated from the soluble copper sulfate solution using filtration. c) To obtain crystals, the student should pour the copper sulfate solution into an evaporating basin and heat it gently with a Bunsen burner to evaporate some of the water, concentrating the solution until the crystallization point is reached (when crystals start to form on a cold glass rod). The heating is stopped, and the solution is left to cool slowly so that large crystals form. Finally, the crystals are filtered to separate them from any remaining liquid and gently patted dry using filter paper or left in a warm place to dry. d) Reacting copper carbonate (a metal carbonate) with sulfuric acid produces carbon dioxide gas in addition to copper sulfate and water. This means you would observe effervescence (bubbles/fizzing), which is not observed with copper oxide.

a) 1 mark for the correct word equation: copper oxide + sulfuric acid -> copper sulfate + water. b) i) 1 mark for ensuring all the acid reacts / is neutralized. ii) 1 mark for stating that a black solid remains at the bottom of the beaker / stops dissolving. iii) 1 mark for 'filtration' / 'filtering'. c) 3 marks: 1 mark for heating/evaporating the solution to concentrate it / evaporate some water. 1 mark for leaving the solution to cool and crystallize. 1 mark for filtering the crystals and drying them (with filter paper / in a warm oven). d) 2 marks: 1 mark for stating there would be bubbles / fizzing / effervescence. 1 mark for explaining this is because carbon dioxide gas is produced.

a) Temperature change = Final temperature - Initial temperature = \(11.5\text{ }^\circ\text{C} - 20.2\text{ }^\circ\text{C} = -8.7\text{ }^\circ\text{C}\) (a temperature decrease of \(8.7\text{ }^\circ\text{C}\)). b) The reaction is endothermic because the temperature of the reaction mixture decreased, which indicates that energy has been taken in/absorbed from the surroundings. c) In an endothermic reaction, the products have more chemical energy than the reactants. Therefore: i) The line for reactants should be drawn at a lower energy level, and the line for products should be drawn at a higher energy level. ii) The activation energy (\(E_a\)) is represented by an arrow pointing upwards from the reactant energy level to the peak of the curve. The overall energy change (\(\Delta H\)) is represented by an arrow pointing upwards from the reactant energy level to the product energy level. d) A common everyday use of an endothermic reaction is in chemical cold packs, which are used to treat sports injuries by cooling the affected area. e) Activation energy is defined as the minimum amount of energy that reacting particles must have when they collide in order to successfully break bonds and start a chemical reaction.

a) 1 mark for -8.7 (or a decrease of 8.7). (Accept 8.7 only if the word 'decrease' is explicitly stated). b) 2 marks: 1 mark for 'endothermic', 1 mark for explaining that the temperature decreased / energy was taken in from the surroundings. c) 4 marks: 1 mark for stating reactant line is lower than product line. 1 mark for identifying the correct labels for reactants and products. 1 mark for describing the activation energy arrow pointing from reactants to the peak of the curve. 1 mark for describing the overall energy change arrow pointing from reactants to products. d) 1 mark for 'instant cold pack' / 'cooling pack'. e) 1 mark for stating it is the minimum energy required for particles to react / for successful collisions.

a) Different structural forms of the same element are called allotropes. b) In diamond, each carbon atom is bonded to four other carbon atoms in a giant covalent structure. The bonding forms a rigid, three-dimensional tetrahedral network. c) In graphite, each carbon atom is covalently bonded to only three other carbon atoms, forming flat hexagonal layers. There are no covalent bonds between the layers, only weak intermolecular forces holding them together. d) Graphite is soft and slippery because there are only weak forces between the layers of carbon atoms. This allows the layers to easily slide over one another. Diamond is extremely hard because it has a giant three-dimensional covalent lattice where all atoms are held in place by strong covalent bonds in all directions, which require a massive amount of force to break. e) In graphite, because each carbon atom forms only three covalent bonds, there is one electron from each carbon atom's outer shell that is not involved in bonding. These electrons become delocalised and are free to move throughout the structure of graphite to carry an electrical current. In diamond, all four outer-shell electrons of each carbon atom are held in localized covalent bonds, so there are no free-moving delocalised electrons to carry charge.

a) 1 mark for 'allotropes' / 'allotropy'. b) 2 marks: 1 mark for stating each carbon atom is bonded to 4 other carbon atoms. 1 mark for identifying that these are covalent bonds / form a giant tetrahedral structure. c) 2 marks: 1 mark for stating each carbon atom is bonded to 3 other carbon atoms in layers / hexagonal rings. 1 mark for mentioning weak forces between layers. d) 2 marks: 1 mark for explaining that the layers in graphite can slide over each other due to weak forces between them. 1 mark for explaining that diamond is hard because of its rigid 3D giant structure of strong covalent bonds. e) 2 marks: 1 mark for stating that graphite has delocalised electrons that are free to move and carry electrical charge. 1 mark for stating that diamond has no free / delocalised electrons because all outer electrons are shared in covalent bonds.

a) \(M_r(\text{Na}_2\text{CO}_3) = (2 \times 23) + 12 + (3 \times 16) = 46 + 12 + 48 = 106\). b) i) The reaction produces carbon dioxide gas which escapes into the surrounding atmosphere, meaning there is less solid mass remaining in the test tube. ii) According to the law of conservation of mass, the total mass of reactants equals the total mass of products: \(\text{Mass of reactant (10.0 g)} = \text{Mass of CaO (5.6 g)} + \text{Mass of }\text{CO}_2\). Therefore, \(\text{Mass of }\text{CO}_2 = 10.0\text{ g} - 5.6\text{ g} = 4.4\text{ g}\). c) First, calculate the relative formula mass of methane: \(M_r(\text{CH}_4) = 12 + (4 \times 1) = 16\). Next, calculate the number of moles of methane: \(\text{Moles of }\text{CH}_4 = \frac{\text{mass}}{M_r} = \frac{3.2}{16} = 0.2\text{ moles}\). According to the balanced equation, 1 mole of \(\text{CH}_4\) reacts with 2 moles of \(\text{O}_2\). So, the moles of oxygen required = \(0.2 \times 2 = 0.4\text{ moles}\). The relative formula mass of oxygen gas (\(\text{O}_2\)) is \(2 \times 16 = 32\). Finally, calculate the mass of oxygen: \(\text{Mass of }\text{O}_2 = \text{moles} \times M_r = 0.4 \times 32 = 12.8\text{ g}\).

a) 2 marks: 1 mark for showing correct working, e.g., \((2 \times 23) + 12 + (3 \times 16)\). 1 mark for correct answer: 106. b) i) 1 mark for stating that carbon dioxide gas is produced and escapes into the atmosphere. ii) 2 marks: 1 mark for showing correct subtraction: \(10.0 - 5.6\). 1 mark for correct answer: \(4.4\text{ g}\). c) 4 marks: 1 mark for calculating \(M_r\) of \(\text{CH}_4 = 16\) and/or finding moles of \(\text{CH}_4 = 0.2\). 1 mark for using the correct 1:2 molar ratio to find moles of \(\text{O}_2 = 0.4\). 1 mark for calculating \(M_r\) of \(\text{O}_2 = 32\). 1 mark for correct final mass of \(12.8\text{ g}\) (allow error carried forward - ecf - if previous steps had arithmetic errors).

a) The atomic number is the number of protons, which is 3. Since it is a neutral atom, the number of electrons is also 3. The number of neutrons is the mass number minus the atomic number: \(7 - 3 = 4\).

b) Protons have a positive charge (+1) and electrons have a negative charge (-1). Because there are equal numbers of protons (3) and electrons (3) in the atom, the charges cancel each other out completely.

c) Isotopes have the same number of protons but different numbers of neutrons. Lithium-6 has 3 neutrons (calculated as \(6 - 3 = 3\)), whereas Lithium-7 has 4 neutrons (calculated as \(7 - 3 = 4\)). Therefore, Lithium-6 has 1 fewer neutron than Lithium-7.

d) To calculate the relative atomic mass: \(A_r = \frac{(92.5 \times 7) + (7.5 \times 6)}{100} = \frac{647.5 + 45}{100} = \frac{692.5}{100} = 6.925\). Rounding to 2 decimal places gives 6.93.

a) [3 marks]
- 1 mark for 3 protons
- 1 mark for 4 neutrons
- 1 mark for 3 electrons

b) [2 marks]
- 1 mark for stating that it contains equal numbers of protons and electrons
- 1 mark for explaining that protons are positive and electrons are negative (so charges cancel/balance each other)

c) [2 marks]
- 1 mark for stating that Lithium-6 has fewer neutrons (or 3 neutrons instead of 4)
- 1 mark for stating that they have the same number of protons / electrons

d) [2 marks]
- 1 mark for correct substitution into formula: \(\frac{(92.5 \times 7) + (7.5 \times 6)}{100}\) or \(\frac{692.5}{100}\)
- 1 mark for correct final answer of 6.93 (Award 1 mark if final answer is 6.9 or 6.925 but working is shown)

a) Temperature change = final temperature - initial temperature = \(14.0 \text{ °C} - 20.5 \text{ °C} = -6.5 \text{ °C}\) (a decrease of 6.5 °C).

b) The reaction is endothermic because the temperature decreased, which shows that heat energy was taken in from the surroundings.

c) To make it a fair comparison, the independent variable (mass of sodium hydrogencarbonate) is changed, while other variables must be controlled. These include the volume of the citric acid solution (50 cm³), the starting temperature of the acid, the concentration of the citric acid, and the rate of stirring.

d) Polystyrene is a good thermal insulator compared to glass. In an endothermic reaction, heat enters the reaction mixture from the surroundings. A polystyrene cup minimizes this thermal energy transfer, resulting in a more accurate temperature drop measurement.

e) Since this is an endothermic reaction, energy is absorbed from the surroundings. This energy is stored in the chemical bonds of the products. Thus, the products have more energy than the reactants.

a) [1 mark]
- 1 mark for (-)6.5 (°C)

b) [2 marks]
- 1 mark for endothermic
- 1 mark for stating that the temperature decreased / fell / energy was taken in

c) [2 marks]
- 1 mark each for any two of: volume of citric acid, concentration of citric acid, starting temperature of the acid, or same rate of stirring. (Do not accept 'mass of sodium hydrogencarbonate')

d) [2 marks]
- 1 mark for stating polystyrene is a thermal insulator / poor conductor of heat
- 1 mark for explaining that this reduces heat transfer / heat entering from the surroundings

e) [2 marks]
- 1 mark for stating that energy is absorbed / taken in from the surroundings
- 1 mark for stating that the products have more energy than the reactants

a) When a metal carbonate reacts with an acid, the products are a salt, carbon dioxide, and water. Therefore, the word equation is:
copper carbonate + sulfuric acid \(\rightarrow\) copper sulfate + carbon dioxide + water.

b) Copper carbonate is a green powder that reacts with sulfuric acid to release carbon dioxide gas. When the acid has reacted completely, no more carbon dioxide is produced, so fizzing stops. Because the excess copper carbonate cannot react further, it remains as an insoluble green solid at the bottom of the beaker.

c) Filtration is carried out to separate the insoluble excess copper carbonate (the residue) from the soluble copper sulfate solution (the filtrate).

d) To obtain dry, pure crystals:
1. Heat the copper sulfate solution in an evaporating basin gently (using a water bath or Bunsen burner) to evaporate some of the water until the crystallization point is reached.
2. Leave the solution to cool and crystallize slowly at room temperature.
3. Filter the crystals from the remaining solution, then gently pat them dry with filter paper (or leave them in a warm oven/dry place).

a) [2 marks]
- 1 mark for correct reactants: copper carbonate + sulfuric acid
- 1 mark for correct products: copper sulfate + carbon dioxide + water (deduct 1 mark if chemical formulas are used incorrectly)

b) [2 marks]
- 1 mark for fizzing / effervescence / bubbling stops
- 1 mark for green solid / powder remains at the bottom (does not dissolve/disappear)

c) [2 marks]
- 1 mark for explaining that it removes the unreacted / excess copper carbonate
- 1 mark for identifying that copper carbonate is insoluble while the copper sulfate is soluble (filtrate)

d) [3 marks]
- 1 mark for heating/evaporating the solution to the point of crystallization
- 1 mark for leaving the solution to cool and crystallize slowly
- 1 mark for filtering the crystals and drying them (e.g., using filter paper or a warm oven)

**Part a:** A gas syringe is commonly used to collect and measure the volume of gas. Alternatively, a measuring cylinder inverted in water can be used.

**Part b:** Smaller marble chips have a larger surface area (for the same mass/volume). This increases the surface area to volume ratio, meaning more particles are exposed at the surface. Consequently, there are more frequent collisions between the hydrochloric acid particles and the calcium carbonate, which increases the rate of reaction.

**Part c:** The gradient of the graph is steepest at the start because the concentration of reactants is at its highest, so the rate of reaction is fastest. As the reactants are used up, their concentration decreases, so the rate of reaction slows down and the gradient becomes less steep. The graph becomes flat (horizontal) because the reaction has stopped as one of the reactants has been completely used up.

**Part d:**
First, convert the time from minutes to seconds:
\(1.5 \text{ minutes} = 1.5 \times 60 = 90 \text{ seconds}\).
Then, calculate the mean rate of reaction:
\(\text{Mean rate} = \frac{\text{volume of gas}}{\text{time}} = \frac{45 \text{ cm}^3}{90 \text{ s}} = 0.5 \text{ cm}^3/\text{s}\).

**Part a (1 mark):**
- 1 mark: gas syringe OR measuring cylinder (inverted in a water trough / over water).

**Part b (3 marks):**
- 1 mark: (smaller chips have a) larger surface area to volume ratio.
- 1 mark: more frequent collisions (between reactant particles / acid and carbonate).
- 1 mark: (resulting in a) faster rate of reaction / more successful collisions per second.

**Part c (3 marks):**
- 1 mark: gradient decreases / becomes less steep as time goes on (or steepest at start).
- 1 mark: line becomes flat / horizontal (at the end).
- 1 mark: because the reaction stops as a reactant / acid / carbonate is completely used up / runs out.

**Part d (3 marks):**
- 1 mark: conversion of minutes to seconds: \(1.5 \times 60 = 90\) (s).
- 1 mark: formula/calculation: \(45 / 90\).
- 1 mark: correct value with unit: \(0.5\) cm³/s.

**Part a:** Crude oil is heated to vaporise it. The vapour enters a fractionating column, which has a temperature gradient (it is hot at the bottom and cooler at the top). The vapours rise up the column. Hydrocarbons condense when they reach the level that is at a temperature below their boiling point. Long-chain hydrocarbons have high boiling points and condense near the bottom, while short-chain hydrocarbons have low boiling points and condense or exit as gases near the top.

**Part b:** The general formula for alkanes is \(\text{C}_n\text{H}_{2n+2}\).

**Part c (i):** Cracking is a thermal decomposition reaction (breaking down molecules using heat).

**Part c (ii):** Catalytic cracking requires high temperatures (approx. 500 °C) and a catalyst (such as alumina/zeolite).

**Part d:** To balance the atoms on both sides of the equation:
Carbon atoms: \(10 - 8 = 2\).
Hydrogen atoms: \(22 - 18 = 4\).
So, the formula of the missing product is \(\text{C}_2\text{H}_4\) (ethene).

**Part a (4 marks):**
- 1 mark: crude oil is heated / vaporised.
- 1 mark: column is hotter at the bottom and cooler at the top (temperature gradient).
- 1 mark: hydrocarbons condense at their boiling points / different temperatures.
- 1 mark: smaller molecules with lower boiling points condense higher up the column (or vice versa).

**Part b (1 mark):**
- 1 mark: \(\text{C}_n\text{H}_{2n+2}\).

**Part c (i) (1 mark):**
- 1 mark: thermal decomposition.

**Part c (ii) (2 marks):**
- 1 mark: high temperature / heat.
- 1 mark: catalyst / zeolite / alumina.

**Part d (2 marks):**
- 2 marks: \(\text{C}_2\text{H}_4\) (or ethene).

**Part a:** Coal contains sulfur impurities. When coal is burned, the sulfur reacts with oxygen from the air to form sulfur dioxide gas (\(\text{SO}_2\)). This gas rises into the atmosphere and dissolves in water droplets in clouds to form sulfuric acid, resulting in acid rain.

**Part b (i):** In a car engine, the combustion of fuel generates very high temperatures. These high temperatures cause nitrogen and oxygen, which are both naturally present in the air, to react together to form oxides of nitrogen.

**Part b (ii):** Oxides of nitrogen cause acid rain and photochemical smog. They can also cause or worsen respiratory symptoms/asthma in humans.

**Part c (i):** During incomplete combustion (which occurs when there is insufficient oxygen), the carbon in the fuel is not fully oxidised. The products formed (excluding water) are carbon monoxide (\(\text{CO}\)) and carbon (in the form of soot/particulates).

**Part c (ii):** Carbon monoxide is toxic because it binds strongly to the haemoglobin in red blood cells in place of oxygen. This prevents oxygen from being carried around the body to organs and tissues, leading to suffocation or death.

**Part a (3 marks):**
- 1 mark: sulfur reacts with oxygen (during combustion) to form sulfur dioxide.
- 1 mark: sulfur dioxide dissolves in water / rainwater / water droplets in clouds.
- 1 mark: to form an acid / sulfuric acid (which falls as acid rain).

**Part b (i) (2 marks):**
- 1 mark: (very) high temperatures (inside the car engine).
- 1 mark: cause nitrogen and oxygen (from the air) to react together.

**Part b (ii) (1 mark):**
- 1 mark: any one from: acid rain, respiratory problems / asthma, smog / photochemical smog.

**Part c (i) (2 marks):**
- 2 marks: carbon monoxide AND carbon / soot (particulates). (1 mark for either).

**Part c (ii) (2 marks):**
- 1 mark: binds to haemoglobin (in red blood cells).
- 1 mark: reduces the capacity of blood to carry oxygen.

**Part a:** The diagram must show:
1. A beaker containing a solvent (e.g., water).
2. Chromatography paper suspended inside the beaker with the start line (pencil line) above the level of the solvent.
3. A spot of food dye on the start line.

**Part b:** Pencil lead is made of graphite, which is insoluble in chromatography solvents. It will not dissolve or run up the paper. Ink, however, is soluble in many solvents and would separate into its own components, interfering with the chromatogram.

**Part c (i):**
\[R_{\text{f}} = \frac{\text{distance moved by substance}}{\text{distance moved by solvent front}}\]

**Part c (ii):**
Using the formula:
\[R_{\text{f}} = \frac{3.2 \text{ cm}}{8.0 \text{ cm}} = 0.40\]

**Part d:** A formulation is a complex mixture that has been designed as a useful product, where every ingredient is carefully measured to ensure the product has the required properties (e.g., medicines, paints, fuels). A pure substance consists of only one element or one compound, with no other substances mixed with it.

**Part a (3 marks):**
- 1 mark: diagram showing paper suspended in a beaker/container with solvent at the bottom.
- 1 mark: pencil/start line is clearly drawn above the solvent level.
- 1 mark: clear labels: 'paper' / 'chromatography paper', 'solvent' / 'water', and 'start line' / 'pencil line' / 'spot'.

**Part b (2 marks):**
- 1 mark: pencil (graphite) is insoluble (in the solvent) / will not run.
- 1 mark: ink is soluble (in the solvent) / ink would run / ink would separate.

**Part c (i) (1 mark):**
- 1 mark: \(R_{\text{f}} = \text{distance moved by substance} / \text{distance moved by solvent (front)}\).

**Part c (ii) (2 marks):**
- 1 mark: calculation \(3.2 / 8.0\).
- 1 mark: correct answer of \(0.4\) or \(0.40\).

**Part d (2 marks):**
- 1 mark: formulation is a mixture designed as a useful product (made of specific proportions).
- 1 mark: pure substance consists of only a single element or compound.

**Part a:** The four stages of a life cycle assessment are:
1. Extracting and processing raw materials.
2. Manufacturing and packaging.
3. Use and operation during its lifetime.
4. Disposal at the end of its useful life (including transport/recycle/waste).

**Part b:**
*Advantage of paper:* Paper is biodegradable (will decompose naturally) and comes from a renewable resource (trees), unlike plastic which is non-biodegradable and made from finite crude oil.
*Disadvantage of paper:* Making paper bags requires a vast amount of water and energy, and can lead to deforestation if not managed sustainably; paper bags are also less durable and typically used fewer times than plastic bags.

**Part c:** Extracting aluminium from its ore (bauxite) requires mining, which destroys habitats, and electrolysis, which uses huge amounts of electricity. Recycling aluminium saves about 95% of this energy, reducing greenhouse gas emissions (since less fossil fuel is burned for electricity). It also conserves the finite reserves of bauxite ore and reduces the amount of waste sent to landfill sites.

**Part a (4 marks):**
- 1 mark: extracting / obtaining and processing raw materials.
- 1 mark: manufacturing and packaging.
- 1 mark: use / operation / reuse during its lifetime.
- 1 mark: disposal / end of life.

**Part b (2 marks):**
- 1 mark: any valid advantage of paper (e.g. biodegradable, made from renewable source).
- 1 mark: any valid disadvantage of paper (e.g. requires chopping down trees, high water usage in production, low durability).

**Part c (4 marks):**
- 1 mark: recycling uses significantly less energy / electricity than extraction.
- 1 mark: extraction of aluminium requires electrolysis which is highly energy-intensive.
- 1 mark: conserves finite resources / bauxite ore.
- 1 mark: reduces environmental impact of mining OR reduces landfill waste.

**Part a:** Today's atmosphere contains approximately 78-80% nitrogen and 20-21% oxygen.

**Part b (i):** Volcanic activity released large amounts of carbon dioxide (\(\text{CO}_2\)) and water vapour (\(\text{H}_2\text{O}\)). (Nitrogen, methane, and ammonia are also acceptable).

**Part b (ii):** As the Earth cooled down from its early hot state, the water vapour in the atmosphere condensed into liquid water. This water fell as rain and gathered in hollows on the Earth's surface, forming the oceans.

**Part c:** Algae and simple plants evolved first in the oceans (around 2.7 billion years ago). These organisms carried out photosynthesis, which uses carbon dioxide and water to produce glucose and oxygen gas (\(\text{O}_2\)). Over billions of years, as plant life flourished and colonized land, the percentage of oxygen increased to its current level.

**Part d:** The percentage of carbon dioxide decreased because:
1. It dissolved in the newly formed oceans to form soluble carbonate compounds and precipitate as sedimentary rocks (e.g., limestone).
2. It was absorbed by algae and plants for photosynthesis.
3. It became locked up in fossil fuels (coal, crude oil, gas) when organisms died and were buried.

**Part a (2 marks):**
- 1 mark: nitrogen ~80% (accept 78% or 78-80%).
- 1 mark: oxygen ~20% (accept 21% or 20-21%).

**Part b (i) (2 marks):**
- 2 marks: any two from: carbon dioxide, water vapour, nitrogen, methane, ammonia. (1 mark for each).

**Part b (ii) (2 marks):**
- 1 mark: Earth cooled (down).
- 1 mark: water vapour condensed (to form liquid water / rain which filled oceans).

**Part c (2 marks):**
- 1 mark: (evolution of) algae / plants.
- 1 mark: photosynthesised / carried out photosynthesis (releasing oxygen).

**Part d (2 marks):**
- 2 marks: any two reasons from: carbon dioxide dissolved in the oceans; formed insoluble carbonates / sedimentary rocks; absorbed by plants/algae for photosynthesis; became locked up in fossil fuels / shells.

**Part a:**
1. Electromagnetic radiation with short wavelengths (such as UV and visible light) from the Sun passes through the Earth's atmosphere.
2. The Earth's surface absorbs this short wavelength radiation and warms up.
3. The Earth then re-emits this energy as longer wavelength infrared (thermal) radiation.
4. Greenhouse gases in the atmosphere absorb this long wavelength infrared radiation, trapping the energy and preventing it from escaping back into space, which warms the atmosphere.

**Part b:** Human activities that release methane include:
1. Agriculture: raising livestock (especially cattle/cows, which release methane from digestion).
2. Landfill sites: decay of organic waste by anaerobic bacteria releases methane.
3. Rice fields: anaerobic decomposition in flooded rice paddies.

**Part c:** Effects of climate change include: rising sea levels (due to melting glaciers and thermal expansion of oceans), loss of habitats/biodiversity, more frequent and severe extreme weather events (such as droughts, floods, hurricanes), and changes in rainfall patterns affecting agriculture.

**Part d:** The carbon footprint is the total amount of carbon dioxide and other greenhouse gases emitted over the full life cycle of a product, service, or event.

**Part a (4 marks):**
- 1 mark: short wavelength radiation (from Sun) passes through the atmosphere.
- 1 mark: Earth's surface absorbs this radiation (and warms up).
- 1 mark: Earth re-emits long wavelength (infrared / thermal) radiation.
- 1 mark: greenhouse gases absorb this long wavelength radiation (trapping heat).

**Part b (2 marks):**
- 2 marks: any two from: cattle/livestock farming, landfill decay, rice cultivation/paddies, extraction/burning of fossil fuels. (1 mark for each).

**Part c (2 marks):**
- 2 marks: any two from: melting ice caps / glaciers, rising sea levels, coastal flooding, extreme weather events, loss of habitats, desertification. (1 mark for each).

**Part d (2 marks):**
- 1 mark: total amount of carbon dioxide and other greenhouse gases (emitted).
- 1 mark: over the full life cycle of a product, service, or event.

**Part a:** The symbol used is \(\rightleftharpoons\).

**Part b (i):** Cooling the reaction mixture (decreasing the temperature) will decrease the yield of ammonia. This is because, according to Le Chatelier's Principle, a decrease in temperature causes the position of equilibrium to shift in the exothermic direction (which is the reverse reaction) to produce more heat. Therefore, more ammonium chloride is formed, and less ammonia is produced.

**Part b (ii):** Since the forward reaction is endothermic, the reverse reaction must be exothermic.

**Part c:** Dynamic equilibrium means:
1. The rate of the forward reaction is equal to the rate of the reverse reaction.
2. The reaction is continuous (both forward and reverse reactions are still happening).
3. The concentrations of reactants and products remain constant (do not change).

**Part d:** Dynamic equilibrium can only be achieved in a closed system. This is because a closed system prevents any reactants or products from escaping into the surroundings, ensuring they remain in contact and are available to react in both directions.

**Part a (1 mark):**
- 1 mark: \(\rightleftharpoons\).

**Part b (i) (3 marks):**
- 1 mark: (yield of ammonia) decreases.
- 1 mark: because the reverse reaction is exothermic.
- 1 mark: (according to Le Chatelier's Principle) the equilibrium shifts in the exothermic direction / to the left to oppose the decrease in temperature.

**Part b (ii) (1 mark):**
- 1 mark: exothermic.

**Part c (3 marks):**
- 1 mark: rate of forward reaction is equal to rate of reverse reaction.
- 1 mark: concentrations of reactants and products remain constant.
- 1 mark: both forward and reverse reactions are still occurring.

**Part d (2 marks):**
- 1 mark: (closed system) prevents reactants/products from escaping (to surroundings).
- 1 mark: so that they can react together.

Part a: Safety goggles should be worn because dilute acid is an irritant.
Part b: A gas syringe is used to collect and measure the exact volume of gas produced.
Part c: Mean rate = volume of gas / time = \(24\text{ cm}^3 / 30\text{ s} = 0.8\text{ cm}^3/\text{s}\).
Part d: The rate is highest at the start because the concentration of reactants is at its peak. The reaction slows down as reactants are used up, and eventually stops (rate becomes zero) when one of the reactants is completely depleted.
Part e: Using powder increases the surface area of the calcium carbonate. This increases the frequency of collisions between the acid particles and the solid reactant, which increases the rate of reaction.

Part a [1 mark]:
- 1 mark: Wear safety goggles / safety glasses / protective gloves.

Part b [1 mark]:
- 1 mark: Gas syringe (allow measuring cylinder inverted over water).

Part c [3 marks]:
- 1 mark: Correct substitution into rate equation: \(24 / 30\)
- 1 mark: Correct calculation: \(0.8\)
- 1 mark: Correct unit: \(\text{cm}^3/\text{s}\) or \(\text{cm}^3\text{ s}^{-1}\)

Part d [2 marks]:
- 1 mark: Correctly states that the reaction slows down / rate decreases over time.
- 1 mark: Correctly states that the reaction stops (rate is zero) / line goes flat.

Part e [3 marks]:
- 1 mark: Rate of reaction increases / reaction goes faster.
- 1 mark: Powder has a larger surface area (for the same mass).
- 1 mark: More frequent collisions (between reactant particles).

Part a: Pencil lead is graphite, which is insoluble in the solvent and will not run or interfere with the chromatogram.
Part b: If the solvent level is above the start line, the food colouring spots will dissolve directly into the solvent in the beaker rather than traveling up the chromatography paper.
Part c: \(R_f = \frac{4.5\text{ cm}}{6.0\text{ cm}} = 0.75\).
Part d:
(i) A formulation is a complex mixture designed as a useful product, where each substance has a specific purpose and is measured in precise quantities.
(ii) A pure substance will only produce one single spot on the chromatogram because it consists of a single compound. A formulation (which is a mixture of substances) will separate into multiple spots because it contains multiple compounds with different solubilities.

Part a [1 mark]:
- 1 mark: Pencil is insoluble (in water/solvent) / ink is soluble so ink would run/smudge.

Part b [2 marks]:
- 1 mark: If above the line, the samples/spots will dissolve in the solvent / wash off the paper.
- 1 mark: They would not travel up the paper / chromatogram would fail.

Part c [2 marks]:
- 1 mark: Correct substitution: \(4.5 / 6.0\)
- 1 mark: Correct calculation: \(0.75\) (Accept no units; penalize if units are given).

Part d(i) [2 marks]:
- 1 mark: A mixture designed as a useful product.
- 1 mark: Component quantities are carefully measured / each component has a specific function.

Part d(ii) [3 marks]:
- 1 mark: Pure substance produces only one spot.
- 1 mark: Formulation / mixture separates into more than one spot / multiple spots.
- 1 mark: Linked explanation (e.g., because different substances in the mixture have different solubilities/affinities).