C10.1 · Sustainable development and life cycle assessment
Show — 3 marks
A manufacturing company produces plastic bottles from crude oil. The company wants to reduce its environmental impact and is considering switching to recycled plastic for bottle production. Life cycle assessment (LCA) is being used to evaluate the environmental cost of both processes, including raw material extraction, manufacturing, transportation, and disposal.
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(a) Show that using recycled plastic instead of crude oil-derived plastic reduces the energy required during the raw material extraction stage of the life cycle.
[1 mark]
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(b) Explain why life cycle assessment is a useful tool for identifying the most sustainable option when choosing between new plastic and recycled plastic for bottle manufacture.
[2 marks]
Show mark scheme
- (a) Recycled plastic requires collection and sorting only / crude oil extraction requires drilling, pumping, and refining which uses more energy
- (a) OR: Recycled plastic is already in polymer form so less processing energy is needed / crude oil must be broken down and converted to plastic polymers
- (b) LCA considers all stages of production from cradle to grave / considers the full environmental impact not just one stage
- (b) Allows comparison of different options / shows which process has the lowest overall environmental cost / identifies which stage has the greatest environmental impact
C9.2 · Greenhouse gases and climate change
Show — 3 marks
A chemical manufacturing plant produces ammonia using the Haber process. The plant operates continuously and releases exhaust gases containing unreacted nitrogen, hydrogen, and water vapour into the atmosphere. The plant manager is concerned about the environmental impact and wants to understand which gases contribute to the greenhouse effect and how they trap heat in the atmosphere. The manager has data showing that carbon dioxide levels in the atmosphere have increased by approximately 50% over the last 150 years, correlating with increased industrial activity.
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(a) Show that water vapour is a greenhouse gas but explain why the increase in atmospheric water vapour is not the primary cause of human-induced climate change.
[2 marks]
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(b) The plant manager observes that both carbon dioxide concentration and global temperature have increased over the same 150-year period. Explain why this correlation alone does not prove that increased carbon dioxide is causing climate change, and describe one piece of additional evidence needed to establish a causal link.
[1 mark]
Show mark scheme
- (a) Water vapour absorbs/traps infrared radiation/heat energy reflected from Earth's surface (or equivalent explanation of greenhouse mechanism)
- (a) Water vapour is controlled by the hydrological cycle/evaporation and condensation processes, not by human activity; increased CO₂ is released directly from combustion/industrial processes and accumulates in the atmosphere (or equivalent distinction between natural and anthropogenic sources)
- (b) Correlation does not imply causation; other factors may have changed over 150 years (e.g. solar output, volcanic activity, land use changes) that could also explain the temperature increase; additional evidence needed such as laboratory measurements showing CO₂ absorbs infrared radiation, or isotopic analysis proving the CO₂ comes from fossil fuels, or climate models demonstrating CO₂ alone can reproduce observed warming
C2.1 · Chemical bonds
Show — 4 marks
A student is investigating the properties of three substances: sodium chloride (table salt), diamond, and hydrogen chloride gas. They want to understand why these substances have such different properties despite all containing chemical bonds.
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(a) Sodium chloride has a very high melting point of 801°C, whereas hydrogen chloride gas has a melting point of -114°C. Show that the type of chemical bonding in sodium chloride explains why it has a much higher melting point than hydrogen chloride.
[2 marks]
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(b) Diamond is a form of carbon with a melting point of 3550°C. Show why diamond's melting point is even higher than sodium chloride's, by referring to the structure and bonding in diamond.
[2 marks]
Show mark scheme
- (a) Sodium chloride contains ionic bonds (between Na+ and Cl- ions) / hydrogen chloride contains covalent bonds (between H and Cl atoms) - 1 mark
- (a) Ionic bonds are very strong and require a lot of energy to break, whereas covalent bonds in individual HCl molecules are strong but the intermolecular forces between HCl molecules are weak, so less energy is needed to separate the molecules - 1 mark
- (b) Diamond has a giant covalent structure / macromolecular structure where each carbon atom forms four strong covalent bonds to other carbon atoms in a continuous 3D network - 1 mark
- (b) All the bonds throughout the entire structure must be broken to melt diamond, requiring enormous amounts of energy, whereas in sodium chloride only the ionic bonds need to be broken (the ions can then move freely) - 1 mark
C5.2 · Activation energy and reaction profiles
Compare — 4 marks
A chemical engineer is designing a new industrial process to manufacture ammonia. The process can operate at different temperatures and with or without a catalyst. The engineer has obtained two reaction profile diagrams: one showing the uncatalysed reaction pathway and one showing the same reaction with an iron catalyst present.
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(a) Compare the activation energies shown on the two reaction profile diagrams for the catalysed and uncatalysed ammonia synthesis reactions.
[1 mark]
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(b) Explain why the catalyst lowers the activation energy without being consumed in the reaction.
[2 marks]
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(c) The engineer notes that both reaction profiles show the same overall energy change (ΔH) between reactants and products. Compare and explain why the overall energy change remains the same whether or not a catalyst is used.
[1 mark]
Show mark scheme
- (a) The catalysed reaction has a lower activation energy than the uncatalysed reaction (accept: the catalyst reduces/decreases the activation energy)
- (b) The catalyst provides an alternative reaction pathway with lower activation energy (accept: alternative mechanism/route)
- (b) The catalyst is regenerated at the end of the reaction so it is not consumed/used up (accept: it is reformed/recovered)
- (c) The overall energy change depends only on the energy of reactants and products, not the pathway taken / the catalyst does not change the relative stability of reactants and products (accept: catalysts do not affect the starting or ending energy levels)
C5.1 · Exothermic and endothermic reactions
Evaluate — 3 marks
A student is designing a hand warmer product for use during winter. They are considering two options: Option A uses a chemical reaction that releases heat to the surroundings, while Option B uses a chemical reaction that absorbs heat from the surroundings. The student needs to decide which type of reaction would be more suitable for their hand warmer.
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(a) Identify which type of chemical reaction (exothermic or endothermic) would be suitable for a hand warmer product and explain your choice.
[2 marks]
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(b) Evaluate why the unsuitable reaction type would not work effectively for keeping hands warm.
[1 mark]
Show mark scheme
- (a) Identifies exothermic reaction as suitable for hand warmer
- (b) Explains that exothermic reactions release/give out heat to the surroundings, which would warm the hands
- (b) Evaluates that endothermic reactions absorb heat from surroundings, which would cool the hands rather than warm them / would be ineffective as it removes thermal energy
C7.1 · Hydrocarbons
Describe — 5 marks
Crude oil is separated into useful fractions at a petroleum refinery. The crude oil is heated and passed into a fractionating column. Different hydrocarbon fractions condense at different temperatures and are collected at various levels.
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(a) Describe how the fractionating column separates crude oil into different fractions.
[2 marks]
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(b) Describe the relationship between the size of hydrocarbon molecules and both their boiling points and their uses.
[3 marks]
Show mark scheme
- (a) the column has a temperature gradient (hottest at the bottom, coolest at the top)
- (a) fractions condense at different heights depending on their boiling points / smaller molecules with lower boiling points reach higher up
- (b) larger molecules have higher boiling points (than smaller molecules)
- (b) larger molecules are less volatile / more viscous / less flammable
- (b) smaller molecules are used for fuels (e.g. petrol) while larger molecules are used for lubricating oils / bitumen
C9.1 · The evolution of the atmosphere
Explain — 4 marks
Early Earth's atmosphere was very different from today. Between 4.6 and 2.4 billion years ago, the atmosphere contained almost no free oxygen. Volcanic outgassing released water vapour, carbon dioxide, nitrogen, and trace amounts of other gases. Around 2.4 billion years ago, photosynthetic cyanobacteria began producing oxygen as a waste product. This oxygen initially reacted with dissolved iron in the oceans, forming insoluble iron oxides that settled on the ocean floor. Only after the iron was depleted did oxygen begin to accumulate in the atmosphere, causing the Great Oxidation Event. This shift fundamentally changed atmospheric composition and allowed aerobic life to evolve.
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(a) Explain why oxygen did not accumulate in Earth's atmosphere immediately after cyanobacteria began photosynthesis.
[2 marks]
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(b) Explain how the accumulation of oxygen in the atmosphere would have affected the oxidation of rocks and minerals at Earth's surface.
[2 marks]
Show mark scheme
- (a) Oxygen reacted with dissolved iron in the oceans / formed iron oxides / iron(II) was oxidised to iron(III)
- (a) The oxygen was removed from the atmosphere / consumed in reactions with iron / did not accumulate because it was chemically combined
- (b) Increased oxygen concentration meant more oxidation reactions could occur / rocks and minerals were exposed to higher oxygen concentrations
- (b) Rocks containing metals or other reducing agents would be oxidised more readily / oxidation would be faster or more extensive / this would produce coloured metal oxides such as iron oxides
C10.1 · Sustainable development and life cycle assessment
Explain — 3 marks
A soft drinks company is deciding between plastic PET bottles and returnable glass bottles for packaging their new fruit juice. They are conducting a life cycle assessment to compare the environmental impact of each option.
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(a) Explain one advantage of using returnable glass bottles instead of single-use plastic bottles.
[1 mark]
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(b) Explain why reusing the same glass bottles multiple times reduces the overall environmental impact compared to manufacturing new glass bottles for each use.
[2 marks]
Show mark scheme
- (a) glass bottles can be reused / refilled many times
- (a) glass reduces plastic waste / landfill
- (a) glass does not contribute to ocean pollution / microplastics
- (b) reuse means fewer bottles need to be manufactured
- (b) manufacturing glass requires high temperatures / a lot of energy
- (b) less energy used means less fossil fuel burned / fewer greenhouse gas emissions
- (b) raw materials (sand, limestone) are conserved / less mining needed
C6.2 · Reversible reactions and equilibrium
Explain — 2 marks
The Haber process is an industrial method for producing ammonia by reacting nitrogen gas with hydrogen gas at high temperature and pressure in the presence of a catalyst. The reaction is reversible: \(N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)\). In industry, the conditions are carefully controlled to maximize ammonia production while maintaining economic efficiency. Understanding how equilibrium responds to changing conditions is essential for optimizing this process.
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(a) Explain why increasing the pressure on the equilibrium system shifts the position of equilibrium to the right (towards products).
[1 mark]
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(b) Explain why increasing the temperature of the equilibrium system shifts the position of equilibrium to the left (towards reactants), and why this creates a problem for industrial ammonia production.
[1 mark]
Show mark scheme
- (a) There are 4 moles of gas on the left (1 + 3) and 2 moles on the right; increasing pressure favours the side with fewer moles of gas, so equilibrium shifts right/towards products
- (b) The forward reaction is exothermic, so increasing temperature favours the endothermic reverse reaction, shifting equilibrium left; this reduces ammonia yield/production, which is undesirable economically since less product is formed
C8.2 · Chromatography and tests for gases
Define — 4 marks
A chemistry technician is setting up a laboratory experiment to identify unknown gases produced during a reaction between metals and acids. The technician also needs to separate and identify different coloured dyes in a food sample using paper chromatography. Both techniques are essential quality control methods in the food and chemical industries.
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(a) Define the term Rf value in paper chromatography.
[2 marks]
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(b) Define the term 'mobile phase' in chromatography and state what the mobile phase is in paper chromatography.
[2 marks]
Show mark scheme
- (a) Rf value is the ratio of the distance travelled by a substance to the distance travelled by the solvent (or mobile phase)
- (a) Expressed as a numerical value between 0 and 1 (or as a decimal/fraction)
- (b) Mobile phase is the substance that moves through the chromatography medium / carries the sample through the stationary phase
- (b) In paper chromatography, the mobile phase is the solvent (such as water or ethanol or named appropriate solvent)
C5.1 · Exothermic and endothermic reactions
Show — 5 marks
A chemical manufacturing plant produces calcium oxide (quicklime) by heating calcium carbonate in a kiln. The reaction is: $$\text{CaCO}_3(s) \rightarrow \text{CaO}(s) + \text{CO}_2(g)$$ This is an important industrial process used in cement production and water treatment. The plant manager needs to understand the energy changes involved to optimize the heating system and predict operational costs.
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(a) Show that the decomposition of calcium carbonate is an endothermic reaction by considering the bonds broken and formed during this reaction.
[2 marks]
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(b) The plant operator measures the temperature change when 5.0 g of calcium carbonate is heated strongly in a closed system. The temperature rises from 25°C to 825°C. Explain why the temperature rise does not contradict the fact that this reaction is endothermic.
[3 marks]
Show mark scheme
- (a) Breaking bonds in calcium carbonate requires energy input (endothermic process) / breaking the C=O bonds and Ca-O bonds requires more energy than is released
- (a) Making bonds in calcium oxide and carbon dioxide releases energy but the energy required to break the bonds in calcium carbonate is greater than the energy released when new bonds form
- (b) The external heat source (kiln) provides energy to the system
- (b) The energy from the kiln is used to break the bonds in calcium carbonate (endothermic reaction requires continuous energy input)
- (b) The temperature rise is caused by the continuous supply of heat energy from the external source, not from the reaction itself releasing energy; the reaction is still endothermic because it absorbs more energy than it releases
C10.1 · Sustainable development and life cycle assessment
Suggest — 3 marks
A company manufactures plastic water bottles from crude oil-derived polyethylene terephthalate (PET). Currently, the bottles are single-use and discarded after one week of use. The company is considering three alternatives: (A) making bottles from recycled PET, (B) designing reusable bottles that last for 2 years, or (C) using plant-based bioplastic from corn starch. The company wants to reduce its environmental impact and is conducting a life cycle assessment to compare these options.
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(a) Suggest why a life cycle assessment of the water bottles should include the energy required for recycling and transportation, not just the energy used to manufacture the plastic. (1 mark)
[1 mark]
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(b) Suggest two reasons why option (B), the reusable bottle lasting 2 years, might have a lower overall environmental impact than option (A), the recycled bottle, even if the recycled bottle uses less energy to produce. (2 marks)
[2 marks]
Show mark scheme
- (a) A life cycle assessment must consider all stages from raw material extraction to disposal/recycling; transportation and recycling processes consume energy/resources and produce emissions, so excluding them would give an incomplete/inaccurate picture of the true environmental impact
- (b) Reusable bottles are used multiple times (approximately 100+ times over 2 years) so the environmental cost per use is spread over many uses, whereas recycled single-use bottles must be manufactured and recycled repeatedly
- (b) Reusable bottles reduce the total number of bottles needed/manufactured, reducing overall raw material extraction, manufacturing emissions, and waste produced compared to repeatedly manufacturing and recycling single-use bottles
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