AQA GCSE Chemistry Chemistry Paper 2 (Foundation), June 2023: Question 5

✅ Correct Answers

• Carbon dioxide (✓) [1 mark]
• Methane (✓) [1 mark]

💡 Key Knowledge

The three greenhouse gases you must know for AQA are:

• Carbon dioxide (CO₂)
• Methane (CH₄)
• Water vapour (H₂O)

Nitrogen (N₂) and Oxygen (O₂) make up about 99% of air, but neither is a greenhouse gas.

❌ Common Errors

• Ticking nitrogen or oxygen simply because they are the most abundant atmospheric gases.
• Ticking argon (noble gas, chemically inert, non-greenhouse).
• Ticking more than two boxes, which forfeits marks.

✅ Correct Answer

They maintain temperatures on Earth high enough to support life (or keep the Earth warm enough for organisms to survive).

💡 Key Knowledge

Without the natural greenhouse effect, the average global temperature would be approximately -18°C , meaning liquid water would freeze and Earth would be largely uninhabitable.

🧠 Exam Technique

Always refer to temperature. Phrases like "they give us air to breathe" or "they protect us from the Sun" receive zero marks.

✅ Correct Answer

radiation OR infra-red (radiation) [1 mark]

💡 How the Greenhouse Effect Works

1. Short wavelength radiation (UV and visible light) passes through the atmosphere and warms the Earth's surface.
2. The surface re-emits this energy as long wavelength (thermal / infra-red) radiation.
3. Greenhouse gases absorb this longer wavelength radiation, trapping heat.

❌ Common Errors

• Confusing radiation types: writing "light" or "ultraviolet" instead of radiation or infra-red.
• Confusing the greenhouse effect with the hole in the ozone layer (a completely different atmospheric issue).

✅ Correct Answers

• Higher sea levels (✓) [1 mark]
• Melting polar ice (✓) [1 mark]

🧠 Look Closely at Opposites

Notice the distractor phrasing in the question:

• It says "Fewer droughts" — climate change causes more frequent/severe droughts.
• It says "Fewer storms" — climate change causes more intense storms.
• It says "Less coastal flooding" — rising seas cause more flooding.

💡 Specification Link

Other recognized effects include:

• Changes in rainfall patterns (distribution and quantity).
• Changes to habitats and distribution of wildlife species.
• Stress on food production ecosystems.

📐 Step-by-Step Calculation (Method A)

1. Calculate mass in kg:
   (0.25 / 100) × 350 kg [1 mark]
   = 0.875 kg [1 mark]
2. Convert kg into grams (× 1000):
   0.875 × 1000 = 875 g [1 mark]

Final Answer: 875 g

📐 Alternative Calculation (Method B)

1. Convert total air mass to grams first:
   350 kg × 1000 = 350 000 g [1 mark]
2. Apply the percentage (0.25%):
   (0.25 / 100) × 350 000 g [1 mark]
   = 875 g [1 mark]

Final Answer: 875 g

❌ Calculation Traps & Common Errors

• Forgetting unit conversion: Stopping at 0.875 leaves your answer in kilograms and loses the final conversion mark.
• Dividing instead of multiplying: Dividing by 1000 gives 0.000875 . Remember: 1 kg = 1000 g , so grams must always be a larger number than kilograms.
• Percentage key mistake: Treating 0.25% as 0.25 rather than 0.0025 .