AQA GCSE Chemistry Chemistry Paper 1 (Higher), 2023: Question 10
8 marks · Standard Demand difficulty · Extended Answer
Explain why nanoparticles of titanium dioxide are used for self-cleaning windows and calculate the volume of chlorine gas required to react with 100 kg of titanium dioxide.
Practise this questionQuestion
Question text
10 This question is about titanium dioxide (TiO2).
10.1 Self-cleaning windows are coated with a layer of nanoparticles of titanium dioxide.
Titanium dioxide:
• helps sunlight break down dirt particles
• attracts water, so dirt is washed away by rain.
Nanoparticles of titanium dioxide are used instead of fine particles of titanium dioxide
for coating self-cleaning windows.
Suggest two reasons why.
[2 marks]
10.2 Titanium is extracted from titanium dioxide in a two-stage process.
The equation for the first stage in the process is:
TiO2 + 2 Cl2 + 2 C → TiCl4 + 2 CO
Calculate the volume of chlorine gas needed to react completely with
100 kg of titanium dioxide.
Relative atomic masses (Ar): O = 16 Ti = 48
The volume of one mole of gas = 24 dm3
[6 marks]
Volume = dm3
Mark scheme
Show the mark scheme
AO /
Question Answers Extra information Mark
Spec. Ref.
10.1 allow converse arguments for AO3
fine particles 4.2.4.2
(nanoparticles)
any two from: 2
• have a higher surface area to
volume ratio
• less (material) needed (for the allow a thinner coating is
same effect) needed
• more light gets through
AO /
Spec. Ref.
10.2 (Mr TiO2 =) 80 1 AO2
4.3.1.2
(conversion 100 kg =) 100 000 1 4.3.2.1
(g) 4.3.2.2
4.3.5
100 000 allow correct use of an 1
(moles TiO2= =) incorrectly determined Mr
1250 allow correct use of an incorrect
/ no conversion of mass
(moles Cl2 = 1250 × 2 =) 2500 allow correct use of an 1
incorrectly determined number
of moles of TiO2
(volume Cl2 =) 2500 x 24 allow correct use of an 1
incorrectly determined number
of moles of Cl2
= 60 000 (dm3) 1
Total Question 10 8
How to answer it
Titanium Dioxide: Nanoparticles and Gas Calculations
What this question tests
- Nanoparticles: Understanding why a high surface area to volume ratio makes nanoparticles more efficient than bulk materials.
- Quantitative Chemistry: Converting units (kg to g), calculating moles from mass, using balanced equations for molar ratios, and calculating gas volumes using the 24 dm³ molar volume constant.
Nanoparticles in Coatings
Why use nanoparticles instead of fine particles?
💡 Key Knowledge
- Nanoparticles are 1–100 nm in size.
- They have a very high surface area to volume ratio compared to larger particles.
- This means you need a much smaller amount of the substance to achieve the same effect.
✅ Correct Answers (Any two)
- They have a higher surface area to volume ratio.
- Less material is needed for the same effect (or a thinner coating is needed).
- More light can pass through (they are more transparent).
🧠 Exam Technique
When a question asks you to "suggest" reasons, look at the context. Here, the context is windows. If the coating is made of nanoparticles, it is so thin that it's transparent, which is vital for a window! Always mention surface area to volume ratio when discussing nanoparticles.
The 6-Mark Calculation
Calculating the volume of Chlorine gas
📐 Step-by-Step Calculation
Equation: TiO₂ + 2Cl₂ + 2C → TiCl₄ + 2CO
1 Calculate Mᵣ of TiO₂:
Ti (48) + (2 × O (16)) = 48 + 32 = 80
2 Convert Mass to Grams:
100 kg × 1000 = 100,000 g
3 Calculate Moles of TiO₂:
Moles = Mass / Mᵣ → 100,000 / 80 = 1250 mol
4 Use the Molar Ratio:
From the equation, 1 mole of TiO₂ reacts with 2 moles of Cl₂.
Moles of Cl₂ = 1250 × 2 = 2500 mol
5 Calculate Gas Volume:
Volume = Moles × 24 dm³
Volume = 2500 × 24 = 60,000 dm³
❌ Common Errors
- The "Kilo" Trap: Forgetting to convert 100 kg into 100,000 g. Chemistry calculations almost always require grams.
- Ratio Oversight: Ignoring the "2" in front of Cl₂ in the equation.
- Mᵣ Errors: Using the atomic number instead of the relative atomic mass (Aᵣ).
🧠 Examiner Commentary
This is a "structured" calculation. Even if you get the first step wrong, you can still get "Error Carried Forward" (ECF) marks for the following steps. Always show your working clearly so the examiner can award marks for your process even if the final number is incorrect.
Topics
Chemistry · C2: Bonding, Structure and the Properties of Matter · C3: Quantitative Chemistry
Question and mark scheme from the AQA GCSE Chemistry examination, Chemistry Paper 1 (Higher), 2023. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.