Mark Scheme
Section A — Structured Questions (60 marks)
Question 1 — Atomic structure and the periodic table
(a) 1 mark
(b) 2 marks
- Atoms of the same element [1]
- With different numbers of neutrons / different mass numbers [1]
Accept: same number of protons, different number of neutrons
Accept: same atomic number, different mass numbers
Do not accept: different atomic masses without reference to neutrons/mass number
(c) 3 marks
Method:
- Let X = percentage of X-37, then percentage of X-35 = (100 − X) [1]
- 35.5 = (35 × (100 − X)/100) + (37 × X/100) OR equivalent correct equation [1]
- 70.0% OR 70 % (accept 3 significant figures) [1]
Alternative method:
- Correct rearrangement: X = (35.5 − 35)/(37 − 35) × 100 [2]
- 70.0% [1]
Accept answers showing full working even if not exactly in this format.
Award marks for correct method even if arithmetic error made.
(d) 4 marks
- Reactivity decreases going down Group 7 [1]
- (More) electron shells/energy levels / atoms get larger / increased atomic radius / increased shielding [1]
- (So) weaker attraction between nucleus and incoming/outer electrons [1]
- (So) it is harder to gain an electron / electrons are gained less easily [1]
Accept: harder to attract electrons
Do not accept: "harder to gain a proton"
Do not accept: explanations referring to losing electrons
Question 2 — Structure, bonding and the properties of matter
(a) 3 marks
- Giant metallic (structure) / metallic bonding [1]
- Conducts electricity when solid (and liquid) because it has free/delocalised electrons / mobile electrons [1]
- High melting point because (there are) strong (metallic) bonds / strong forces (between atoms/ions and electrons) that require a lot of energy to overcome [1]
Accept: sea of electrons
Do not accept: "free ions" or "free atoms"
(b) 2 marks
Award marks as follows:
- At least 6 atoms correctly shown (Si and O clearly distinguishable) [1]
- Each silicon joined to 4 oxygens AND each oxygen joined to 2 silicons (giant structure implied) [1]
Accept:
- Ball and stick model OR dot and cross on atoms to distinguish elements
- Any representation that clearly shows the structure
Do not accept:
- Simple molecular diagram (SiO₂ only)
- Diagrams showing SiO₂ in linear arrangement
(c) 3 marks
- (When solid) ions are held in fixed positions / cannot move / are in a lattice [1]
- (When molten) ions are free to move / mobile [1]
- (Moving/mobile) ions carry charge / electricity [1]
Accept: "ions can move when liquid"
Do not accept: "electrons carry the charge" in ionic compounds
Do not accept: "atoms" instead of ions
(d) 2 marks
- Weak intermolecular forces / forces between molecules [1]
- (These forces) require little energy to overcome / are easily broken [1]
Accept: weak van der Waals forces / weak London forces
Do not accept: "weak bonds" without specifying intermolecular
Do not accept: "the molecules break apart"
Question 3 — Quantitative chemistry
(a) 2 marks
- CaCO₃ → CaO + CO₂ [1]
- Balanced (1:1:1) [1]
Accept: state symbols if included correctly
Award [1] only if equation is correct but not balanced
(b) 4 marks
- Mᵣ of CaCO₃ = 40 + 12 + (3 × 16) = 100 [1]
- Moles of CaCO₃ = 25.0 / 100 = 0.25 (mol) [1]
- Mᵣ of CaO = 40 + 16 = 56 (therefore moles of CaO = 0.25) [1]
- Mass of CaO = 0.25 × 56 = 14(.0) g [1]
Accept: alternative valid methods using mass ratio
Award marks for correct method even if Mᵣ calculated incorrectly (consequential marking)
Final answer must be to at least 2 significant figures for final mark
(c) 2 marks
- Percentage yield = (12.6 / 14.0) × 100 [1]
- = 90% (accept 89.9 – 90.0) [1]
Accept: correct answer even if not showing working (both marks)
If using incorrect value from (b), award marks for correct method
(d) 2 marks
Any two from:
- Product left in/on apparatus / lost during transfer [1]
- Some product lost as dust/powder/smoke [1]
- Reaction may be reversible / product may decompose further [1]
- Side reactions occurred [1]
- Impurities in reactants [1]
Do not accept: "human error" without qualification
Do not accept: "not heated for long enough" (contradicts stem)
Question 4 — Chemical changes
(a) 2 marks
- Mg + 2HCl → MgCl₂ + H₂ [1]
- Balanced (with correct formulae) [1]
Accept: correct ionic equation
Accept: state symbols if correct
(b) 2 marks
- Use a lighted splint / lit splint / burning splint [1]
- (Hydrogen) burns with a squeaky pop / makes a squeaky pop sound [1]
Accept: "produces a pop"
Do not accept: just "pop" without "squeaky"
Do not accept: "flammable" without the test described
(c) 2 marks
- Copper is below hydrogen / less reactive than hydrogen (in the reactivity series) [1]
- So copper cannot displace hydrogen (from the acid) / only metals above hydrogen react with acids [1]
Accept: "copper is not reactive enough"
Do not accept: "copper is unreactive" without comparison
(d) 2 marks
- Zn + Cu²⁺ → Zn²⁺ + Cu [1]
- Balanced with correct charges [1]
Award [1] if all species correct but not balanced or charges missing
Do not accept: full equation including sulfate ions
(e) 3 marks
- Carbon / coke / charcoal / carbon monoxide [1]
- Carbon is more reactive than zinc / carbon is above zinc in the reactivity series [1]
- (So) carbon can remove oxygen from zinc oxide / carbon can reduce zinc oxide [1]
Accept: explanation using displacement
Award only [1] if hydrogen or a metal more reactive than zinc is suggested
Do not accept: any substance less reactive than zinc
Question 5 — Energy changes
(a) 1 mark
- As mass increases, temperature change increases / directly proportional / positive correlation [1]
Accept: "temperature decreases more" or "gets colder"
Accept: linear relationship
Do not accept: just "increases" without stating both variables
(b) 1 mark
(c) 3 marks
- Energy is required to break bonds (in the ionic lattice / between ions) [1]
- Energy is released when (new) bonds are made / when ions are hydrated / when water bonds to ions [1]
- More energy is required to break bonds than is released making bonds / energy absorbed is greater than energy released [1]
Accept: "energy needed to break attractions between ions and form attractions to water"
Do not accept: references to breaking molecules without mentioning energy
(d) 2 marks
- Energy per gram = 2940 / 4.0 [1]
- = 735 J/g (accept 740 J/g) [1]
Accept: correct answer with or without working
(e) 4 marks
- Total volume = 25 + 25 = 50 cm³ [1]
- Mass = 50 g (using density = 1.0 g/cm³) [1]
- Q = 50 × 4.2 × 13.5 [1]
- = 2835 J (accept 2800 – 2840 J) OR 2.835 kJ (accept 2.8 – 2.84 kJ) [1]
Award marks for correct method even if arithmetic errors made
Accept: working in stages
Question 6 — The rate and extent of chemical change
(a) 2 marks
- Rate = change in volume / time = 40 / 60 or equivalent from graph [1]
- = 0.67 cm³/s (accept 0.66 – 0.67 cm³/s) [1]
Accept: 0.666... or 2/3
Must include units for second mark
Accept: if different sensible value read from graph and calculated correctly
(b) 2 marks
- A (used higher concentration) [1]
- Steeper curve / reaches the same volume in less time / reacts faster / reaches plateau first [1]
Accept: "gradient is greater" / "rate is faster"
Do not accept: "produces more gas" (both produce same volume)
(c) 2 marks
- One (or both) of the reactants is used up / runs out [1]
- Limiting reactant OR all acid used up OR all marble chips used up [1]
Accept: "no more reactants left to react"
Accept: either reactant specified as used up
Do not accept: vague statements like "reaction finishes" without explanation
(d) 2 marks
- Curve drawn starting at origin [1]
- With lower initial gradient than A, but reaching the same final volume (approximately 120 cm³) [1]
Must be labelled C
Curve should be smooth
Should end at same height as A
(e) 3 marks
- Large marble chips have smaller surface area (to volume ratio) [1]
- Fewer particles are exposed / available for collision (at any time) [1]
- Fewer (successful) collisions per unit time / lower collision frequency (so slower reaction) [1]
Accept: "less area for reaction"
Do not accept: "particles have less energy" (not relevant here)
Do not accept: "particles move slower"
Section B — Extended Response (40 marks)
Question 7 — Evaluating water purification methods
(a) 6 marks
Indicative content:
Distillation:
- Involves heating water to 100°C and condensing steam
- Kills all microbes / bacteria
- Removes all dissolved salts / ions
- Requires large amount of energy / expensive to run
- Produces pure water / very effective
Chlorination:
- Adding chlorine gas or compounds to water
- Kills microbes / bacteria
- Does not remove dissolved salts
- Requires little energy / cheap
- May produce harmful by-products in small amounts
- May affect taste/smell of water
Comparison:
- Distillation more effective at purification but much more expensive
- Chlorination suitable for water with low salt content (UK water)
- Distillation necessary for sea water
- Cost-benefit analysis depends on water source and local conditions
Level 3 (5–6 marks):
A detailed and coherent evaluation comparing both methods. References to effectiveness, energy requirements and suitability are well-developed. Uses correct scientific terminology throughout.
Level 2 (3–4 marks):
Some comparison of methods with reference to at least two of: effectiveness, energy/cost, or suitability. Explanation may lack detail in places. Generally correct use of scientific terminology.
Level 1 (1–2 marks):
Basic statements about one or both methods. Limited or no comparison. May contain inaccuracies. Limited use of scientific terminology.
0 marks: No relevant content.
(b) 9 marks
Indicative content:
How desalination works:
- Distillation: heating sea water and condensing pure water
- Reverse osmosis: forcing water through membrane under pressure
- Both remove dissolved salts
Advantages:
- Provides water in areas with limited fresh water
- Produces water suitable for drinking
- Can use sea water (abundant resource)
- Reliable supply / not dependent on rainfall
- Removes all dissolved salts and impurities
Disadvantages:
- Very high energy requirements
- Expensive to build plants and run them
- Produces carbon dioxide / greenhouse gases (if energy from fossil fuels)
- Produces concentrated brine waste which must be disposed of
- Brine disposal can harm marine ecosystems
- Kills marine organisms if they are drawn into plant
- May not be sustainable long-term
Comparison with other methods:
- Traditional water treatment much cheaper
- Traditional treatment uses much less energy
- Not necessary if fresh water available
- Only worthwhile in water-scarce regions
- May become more important with climate change
Level 3 (7–9 marks):
A comprehensive discussion covering how desalination works, environmental impacts (both positive and negative), and comparison with alternatives. Arguments are well-balanced and developed. Logical structure. Consistently uses correct scientific terminology.
Level 2 (4–6 marks):
Covers at least two of the required areas (process, environment, comparison) with reasonable detail. Some development of ideas but may be unbalanced. Generally correct scientific terminology. Some logical structure.
Level 1 (1–3 marks):
Limited content, may cover only one area or multiple areas with little detail. May be mostly advantages or disadvantages. Limited development. Basic scientific terminology. Little structure to answer.
0 marks: No relevant content.
Question 8 — Using the reactivity series
(a) 6 marks
Indicative content:
Oxidation and reduction:
- Reduction is the removal of oxygen / gain of electrons
- Oxidation is the addition of oxygen / loss of electrons
- Iron oxide loses oxygen → reduction / iron is reduced
- Carbon (in CO) gains oxygen (to form CO₂) → oxidation / carbon is oxidised
- Reduction and oxidation occur together (redox reaction)
Why it shows carbon is more reactive:
- Carbon displaces iron from its oxide
- More reactive element displaces less reactive element
- Carbon has a greater tendency to bond with oxygen than iron does
Why suitable for iron:
- Iron is less reactive than carbon
- Iron is below carbon in the reactivity series
- Carbon is cheap and readily available
Why not suitable for aluminium:
- Aluminium is more reactive than carbon
- Aluminium is above carbon in the reactivity series
- Carbon cannot displace aluminium from its oxide
- Would need electrolysis or a more reactive metal
Level 3 (5–6 marks):
Full explanation covering oxidation and reduction correctly defined, clear explanation of why this demonstrates carbon's greater reactivity, and why method is suitable for iron but not aluminium. Uses correct scientific terminology consistently.
Level 2 (3–4 marks):
Covers oxidation and reduction with mostly correct definitions. Explains some aspects of reactivity. May not fully explain both iron and aluminium. Generally correct terminology.
Level 1 (1–2 marks):
Basic statements about oxidation and/or reduction or reactivity. Limited development. May contain inaccuracies. Limited scientific terminology.
0 marks: No relevant content.
(b) 9 marks
Indicative content:
Why carbon cannot be used:
- Titanium is more reactive than carbon
- Carbon cannot reduce titanium oxide
- Titanium would form carbides (affecting properties)
- Must use more reactive metal to displace titanium
Costs involved:
- Sodium/magnesium are expensive to produce (require electrolysis)
- Multi-stage process (convert to chloride first)
- Batch process (not continuous) increases costs
- High energy requirements
- High temperatures required
- Need to handle reactive metals safely
- Extraction of reactive metal from its ore is expensive
Properties and uses of titanium:
- Strong / high strength
- Low density / light
- Resistant to corrosion
- High melting point
- Biocompatible / does not react with body tissue
- Used in aircraft / aerospace (strong and light)
- Medical implants (biocompatible, strong)
- High-performance applications
Evaluation:
- High cost justified for specialist applications (aircraft, medical)
- Properties make it suitable where other metals would fail
- No suitable cheaper alternatives for these applications
- Small-scale applications can bear the cost
- Not economical for everyday uses
- Cost-benefit depends on application
- Research into cheaper methods ongoing
Level 3 (7–9 marks):
Comprehensive evaluation covering all aspects: why carbon unsuitable, detailed cost factors, properties and uses, and balanced judgement on whether costs justified. Well-structured argument. Consistently correct scientific terminology.
Level 2 (4–6 marks):
Covers most aspects with reasonable detail. Some development of evaluation but may be incomplete or unbalanced. Generally correct scientific terminology. Some structure.
Level 1 (1–3 marks):
Limited content. May focus on only one or two aspects with little development. May be descriptive rather than evaluative. Limited scientific terminology. Little structure.
0 marks: No relevant content.
Question 9 — Explaining trends in the halogens
(a) 2 marks
- Cl₂ + 2Br⁻ → 2Cl⁻ + Br₂ [1]
- Correctly balanced with state symbols OR without (accept either) [1]
Accept: alternative correct ionic representation
Do not accept: full balanced equation with potassium ions
(b) 9 marks
Indicative content:
Trend in reactivity:
- Reactivity decreases down the group
- Fluorine is most reactive, iodine is least reactive
- This is the opposite trend to Group 1
Electronic structure explanation:
- Halogens gain one electron to form 1− ions / to complete outer shell
- Atoms get larger down the group / more electron shells / more shielding
- Outer electrons further from nucleus
- Weaker attraction between nucleus and incoming electron
- Harder to attract/gain an electron
- Takes longer for outer shell to be filled
Evidence from displacement reactions:
- Chlorine displaces both bromine and iodine from solutions
- Shows chlorine is more reactive than bromine and iodine
- Bromine does not displace chlorine
- Shows bromine is less reactive than chlorine
- A more reactive halogen will displace a less reactive halogen
Comparison with Group 1:
- Group 1 metals lose electrons / halogens gain electrons
- In Group 1, reactivity increases down the group
- Larger Group 1 atoms lose electrons more easily (outer electron further from nucleus)
- Larger halogen atoms gain electrons less easily
- Opposite trends because of opposite processes (electron loss vs gain)
Level 3 (7–9 marks):
Comprehensive explanation covering the trend, detailed explanation using electronic structure, clear reference to displacement reactions as evidence, and explanation of why trend is opposite to Group 1. Logical structure and consistently correct scientific terminology.
Level 2 (4–6 marks):
Covers most aspects with some detail. Electronic structure explanation present but may lack full development. References experiments. May not fully explain Group 1 comparison. Generally correct terminology. Some logical structure.
Level 1 (1–3 marks):
Basic statements about trend and/or electronic structure. Limited development. May describe experiments without linking to reactivity. Limited or no comparison with Group 1. Basic terminology.
0 marks: No relevant content.
(c) 4 marks
Indicative content:
Evaluation of hypothesis:
- Hypothesis is incorrect / not supported by evidence
- Boiling point and reactivity are determined by different factors
- No causal link between the two properties
Boiling point explanation:
- Boiling point depends on intermolecular forces / van der Waals forces / London forces
- Larger molecules have stronger intermolecular forces
- More energy required to separate larger molecules
- This explains increasing boiling point down the group
Reactivity explanation:
- Reactivity depends on ability to gain electrons
- Determined by nuclear attraction and electron shielding
- Larger atoms gain electrons less easily
- This explains decreasing reactivity down the group
Conclusion:
- Two properties are not related
- Different types of forces/factors involved
- Student has incorrectly assumed correlation implies causation
Level 3 (4 marks):
Clear evaluation rejecting the hypothesis with full explanation of why boiling point increases (intermolecular forces) while reactivity decreases (electronic structure/electron gain). Uses correct terminology.
Level 2 (2–3 marks):
States hypothesis is incorrect and gives some explanation of either boiling point or reactivity factors, but not both in detail. Some correct terminology.
Level 1 (1 mark):
Basic statement that hypothesis is wrong, or simple description of one property, without developed explanation.
0 marks: No relevant content.
Sample Answers with Examiner Commentary
Question 7(b) — Sample Answers
Grade 9 answer
Desalination is the process of removing salt from sea water to produce potable water. This can be achieved through distillation, which involves heating sea water to 100°C so it evaporates, then condensing the steam to collect pure water. Alternatively, reverse osmosis forces water through a semi-permeable membrane under high pressure, leaving salt and impurities behind.
There are several advantages to desalination. It provides a reliable source of water in coastal areas where fresh water is scarce, such as in the Middle East. This is important because climate change and population growth are increasing water scarcity. Desalination uses sea water, which is abundant, and is not dependent on rainfall. The water produced is very pure as all dissolved salts and microbes are removed, making it safe to drink.
However, there are significant disadvantages, particularly environmental ones. Desalination requires enormous amounts of energy. If this energy comes from fossil fuels, it produces carbon dioxide, a greenhouse gas that contributes to climate change. Building and running desalination plants is extremely expensive. The process also produces concentrated brine as waste, which contains high concentrations of salt and sometimes chemicals used in treatment. When this brine is discharged back into the sea, it can increase salinity in coastal areas, harming marine ecosystems. Fish and other organisms cannot tolerate the high salt concentration. Marine life can also be killed when organisms are drawn into the intake pipes of the plant.
Compared to traditional water treatment methods, desalination is far more expensive and energy-intensive. In countries like the UK with adequate rainfall, traditional treatment of fresh water sources through filtration and chlorination is much more cost-effective and sustainable. However, in areas with limited fresh water, such as desert countries or small islands, desalination may be necessary despite the costs and environmental concerns.
In conclusion, desalination is a useful technology for producing drinking water where alternatives are not available, but its high costs and environmental impacts mean it should only be used when other water sources are insufficient. Investment in renewable energy to power desalination plants could reduce the environmental impact in the future.
Mark: 9/9
Examiner commentary: This is an exemplary answer that addresses all aspects of the question comprehensively. The student clearly explains how desalination works using two methods. The evaluation is balanced, covering multiple advantages (reliability, abundance of sea water, purity) and disadvantages (energy use, greenhouse gases, cost, brine disposal, harm to marine life). The comparison with traditional methods is explicit and well-developed. The answer demonstrates excellent understanding of the chemistry and environmental issues, uses scientific terminology accurately throughout, and presents a logical, well-structured argument with a clear conclusion. This meets all the criteria for Level 3 (7–9 marks) and achieves full marks.
Grade 6 answer
Desalination is when you remove salt from sea water. You can do this by boiling the water and collecting the pure water, or by using reverse osmosis which pushes water through a special filter.
The advantages of desalination are that it can provide water in countries that don't have much fresh water. It's useful in hot countries. The water produced is very clean and safe to drink because the salt has been removed. You can use sea water which there is lots of.
The disadvantages are that desalination uses a lot of energy, which is expensive. This energy produces carbon dioxide which causes global warming. The salt that is left over has to be disposed of and this can harm sea creatures if it is put back in the sea. It also costs a lot of money to build desalination plants.
Compared to normal water treatment, desalination is much more expensive and uses more energy. In the UK we don't need desalination because we have enough rain and rivers, so we can just filter and chlorinate the water which is cheaper. But in countries with no fresh water it might be necessary.
Overall, desalination is good for countries without water but it has problems with cost and the environment.
Mark: 5/9
Examiner commentary: This is a solid mid-level answer that demonstrates reasonable understanding. The student explains how desalination works (though could be more precise about the processes), identifies relevant advantages (provides water in water-scarce areas, purity, sea water abundance) and disadvantages (high energy use, cost, greenhouse gases, brine disposal). There is a comparison with traditional water treatment. However, the answer lacks the depth and development expected at the higher levels. The environmental impacts are mentioned but not fully explained (e.g., how brine harms marine ecosystems, what happens to marine life at intake). The discussion of when desalination is justified could be more developed. Scientific terminology is mostly correct but less sophisticated than the Grade 9 answer. This places the response in Level 2 (4–6 marks).
Grade 3 answer
Desalination is removing salt from water. You boil sea water and the salt is left behind and you get pure water.
Advantages are you can drink the water and it is safe. You can get water in countries that don't have water. There is lots of sea water.
Disadvantages are it costs money and uses energy. The energy is bad for the environment. The salt waste pollutes the sea.
Normal water treatment is better because it's cheaper and you don't have to boil the water, you just filter it and add chlorine. Desalination is only needed if there is no normal water.
Mark: 3/9
Examiner commentary: This answer shows basic understanding but lacks the development required for higher marks. The student mentions desalination only as distillation (no reference to reverse osmosis). Advantages and disadvantages are listed as simple points without explanation—for example, stating "the salt waste pollutes the sea" without explaining the concept of brine or how it harms marine life. The comparison with traditional treatment is superficial. The answer would benefit from: explaining how the environmental damage occurs (e.g., increased salinity, harm to specific organisms); discussing energy requirements in more detail; expanding on when desalination is economically justified; and using more precise scientific terminology. The response demonstrates limited content and structure, placing it in Level 1 (1–3 marks). To improve, the student should develop each point with explanation and use more scientific language.
Question 8(b) — Sample Answers
Grade 9 answer
Titanium cannot be extracted using carbon because titanium is more reactive than carbon in the reactivity series. When carbon is used to reduce titanium oxide, the titanium produced would react with the carbon to form titanium carbide. This makes the titanium brittle and affects its valuable properties, so carbon reduction is not suitable.
Instead, titanium extraction involves several expensive stages. First, titanium oxide is converted to titanium chloride (TiCl₄). Then the titanium chloride must be heated with a more reactive metal such as sodium or magnesium in an argon atmosphere. These metals are themselves expensive to produce because they are very reactive and must be extracted by electrolysis of their molten compounds, which requires large amounts of electrical energy. The titanium extraction process is also a batch process rather than continuous, which increases costs further. The need to handle reactive metals safely and use argon to prevent oxidation adds to the expense.
However, titanium has exceptional properties that justify these high costs for certain applications. It has a low density, making it much lighter than steel, but it also has very high strength. This combination of low density and high strength makes it ideal for aircraft and aerospace applications, where reducing weight improves fuel efficiency and performance. Titanium is also highly resistant to corrosion, even in sea water and acidic conditions, and has a high melting point. Additionally, titanium is biocompatible, meaning it does not react with body tissues or cause rejection, making it ideal for medical implants such as artificial hip joints and dental implants.
For these specialist applications, the high cost is justified because no other materials have the same combination of properties. In aircraft, the weight saving from using titanium instead of steel reduces fuel consumption over the aircraft's lifetime, which can offset the higher initial cost. For medical implants, the biocompatibility means implants can remain in the body for life without causing problems, and the strength ensures they don't fail. However, the cost means titanium is not economical for everyday applications where cheaper materials like steel or aluminium would be sufficient.
In conclusion, although titanium extraction is expensive and energy-intensive, the unique combination of properties makes it essential for high-performance applications where the benefits justify the costs. For general purposes, cheaper alternatives should be used. Research continues into more economical extraction methods, which may make titanium more widely available in the future.
Mark: 9/9
Examiner commentary: This is an outstanding answer that fully addresses all aspects of the question. The student clearly explains why carbon cannot be used (reactivity and carbide formation affecting properties). The discussion of costs is detailed and accurate, covering the multi-stage process, electrolysis requirements, batch processing, handling of reactive metals, and argon atmosphere. The properties of titanium are comprehensively described with accurate scientific terminology (low density, high strength, corrosion resistance, biocompatibility). Most importantly, the evaluation is well-balanced and sophisticated, linking specific properties to specific applications and discussing cost-benefit for different contexts. The student demonstrates the ability to make reasoned judgements about when high costs are justified. The answer is logically structured with a clear conclusion. This meets all Level 3 criteria and achieves full marks.
Grade 6 answer
Carbon cannot be used to extract titanium because titanium is more reactive than carbon. This means carbon cannot displace titanium from titanium oxide. Instead, a more reactive metal like sodium or magnesium is needed.
The costs of extracting titanium are high. Sodium and magnesium are expensive metals to produce because they have to be extracted by electrolysis. The process of extracting titanium has several stages - first making titanium chloride and then reacting it with sodium. This makes it more expensive. It also needs high temperatures which requires a lot of energy.
Titanium has very useful properties. It is strong and light, which makes it good for aircraft. It is also resistant to corrosion, so it doesn't rust. Titanium is used in artificial hip joints because it doesn't react with the body. It also has a high melting point.
The high cost of titanium is justified for important uses like aircraft and medical implants. In aircraft, titanium's low weight means planes use less fuel, which saves money in the long run. For hip joints, titanium lasts a long time in the body without causing problems, so patients don't need replacement operations. However, titanium would not be worth using for everyday objects like cars or buildings because it's too expensive and cheaper metals like steel work fine.
Overall, the extraction of titanium is expensive but worth it for special applications where its properties are needed.
Mark: 6/9
Examiner commentary: This is a competent answer that covers all the required areas but with less depth than the Grade 9 response. The student correctly explains why carbon cannot be used and identifies relevant cost factors (electrolysis of reactive metals, multi-stage process, energy requirements). The properties are accurately stated, and there is some evaluation linking properties to applications. However, the answer lacks detail in places. For example, the student could explain why titanium forms carbides and why this matters, could discuss the batch process nature, and could be more specific about biocompatibility. The evaluation section, while present, is less developed—the aircraft fuel efficiency point is good but could be expanded, and the discussion of when costs are justified could be more nuanced. The answer demonstrates good understanding and uses appropriate terminology, placing it solidly in Level 2 (4–6 marks).
Grade 3 answer
Titanium cannot be extracted with carbon because it is too reactive. You have to use a more reactive metal like sodium instead.
The disadvantages of titanium extraction are that it is very expensive. Sodium is expensive and you need lots of energy. The process has lots of stages which makes it cost more.
Titanium is very useful. It is strong and light so it is used in planes. It doesn't corrode so it lasts a long time. It is also used in hip replacements.
The costs are justified because titanium has good properties. It is needed for planes because it is light and strong. This means planes can fly better. It is also good for medical uses because it is safe in the body.
Titanium is expensive to extract but it is worth it because of its uses.
Mark: 3/9
Examiner commentary: This answer demonstrates basic understanding but lacks development throughout. The student correctly identifies that carbon cannot be used due to reactivity but doesn't explain the displacement principle or mention carbide formation. Cost factors are mentioned but not explained (why is sodium expensive? why do multiple stages increase cost?). Properties are listed without detail (what does "light" mean in terms of density? what is biocompatibility?). The evaluation is superficial, with claims that costs are justified but without well-developed reasoning about cost-benefit. To improve, the student needs to: explain the chemistry behind why carbon doesn't work; develop cost factors (electrolysis, energy, batch process); explain properties using scientific terms (low density