AQA GCSE Chemistry Chemistry Paper 2 (Foundation), June 2024: Question 2

✅ Correct Answer

The rate of global climate change increases.

💡 Key Knowledge

• More furnaces operating → more coal burned → greater mass of CO₂ released into the atmosphere.
• CO₂ is a greenhouse gas that absorbs infrared radiation re-radiated by Earth, enhancing the greenhouse effect and accelerating the rate of global climate change.

📐 Step-by-Step Calculation

Given: 7000 kg of CO₂ is produced when burning 3000 kg of coal.

1 Identify the ratio:
Mass of CO₂ per 1 kg = 7000 ÷ 3000

2 Calculate & round appropriately:
7000 / 3000 = 2.333333...
Answer = 2.33 kg (or rounded correctly to at least 2 significant figures, e.g., 2.3 or 21/3 / 7/3)

❌ Common Calculation Traps

• Dividing the wrong way round: Doing 3000 ÷ 7000 = 0.43 scores 0 marks. Always check: 1 furnace produces more CO₂ (7000 kg) than coal burned (3000 kg), so the answer must be greater than 1!
• Incorrect rounding: Writing 2.32 or rounding 2.333... incorrectly to 2.34 will lose the final accuracy mark.

✅ Correct Answer

Sulfur dioxide causes an environmental effect called acid rain.

💡 Key Knowledge

• Coal contains sulfur impurities. When coal burns, sulfur oxidises:
  S + O₂ → SO₂
• Sulfur dioxide dissolves in atmospheric water vapour forming dilute sulfuric acid (or sulfurous acid), falling as acid rain.
• Acid rain damages limestone buildings, corrodes metals, and damages trees and aquatic life by lowering soil and lake pH.

🧠 How to Plot Figure 3 Accurately

Plot the 5 coordinate pairs from Table 1 (Mass of coal on x-axis, Mass of SO₂ on y-axis):

• Scale reading: On the x-axis, 1 large grid square (10 small squares) = 2000 kg, meaning 1 small square = 200 kg. Therefore, 3000 kg is exactly halfway between 2000 and 4000.
• On the y-axis, 1 large square = 100 kg, meaning 1 small square = 10 kg.
• Line of best fit: Use a sharp pencil and long clear ruler. Draw a single straight line starting from the origin (0,0) passing directly through each plotted cross up to (12000, 400) .

❌ Common Graph Errors

• Missing the (0,0) origin: Students often overlook the very first data row in Table 1 ( 0, 0 ). Don't leave it out!
• Misreading 3000 and 9000: Plotting 3000 at 3 large squares instead of 1.5 large squares.
• Freehand lines: Drawing a wobbly or multiple "feathered" line without a ruler loses the line mark immediately.

✅ Correct Answer

As the mass of coal burned per minute increases, the mass of sulfur dioxide produced per minute increases (or increases proportionally / goes up).

🧠 Exam Technique

Whenever a question starts with "As [variable X] increases, [variable Y]...", look at your graph from left to right. As the line slopes upwards, variable Y increases. State the direct relationship simply without over-complicating it.

✅ Correct Answer

The release of particulates into the air causes global dimming.

💡 Key Knowledge: Combustion Pollutants Summary

• Particulates (soot / unburned carbon): Cause global dimming (they reflect incoming solar radiation back into space) and respiratory health issues in humans.
• Carbon monoxide (CO): Toxic, colourless, and odourless gas that binds to haemoglobin.
• Sulfur dioxide (SO₂) & Nitrogen oxides (NOₓ): Cause acid rain and respiratory problems.
• Carbon dioxide (CO₂): Causes enhanced greenhouse effect and global climate change.