AQA GCSE Combined Science: Trilogy Chemistry Paper 1 (Foundation), June 2025: Question 6

✅ Acceptable Answers (Any One)

• Carry out the experiment in a fume cupboard.
• Carry out the experiment in a well-ventilated room / laboratory (e.g. open windows).
• Use an extractor fan.
• Wear a gas mask / respirator.

❌ Common Errors (Zero Marks)

• "Wear safety goggles" or "Wear gloves": PPE protects eyes and skin, but does not stop you inhaling a poisonous gas!
• Vague answers like "be careful", "stand back", or "wear a mask" without specifying a gas mask.

💡 Scale & Coordinates Guide

Check the axes carefully:

• x-axis (Time): 1 large square (10 small squares) = 100 s → 1 small square = 10 s.
• y-axis (Mass): 1 large square (10 small squares) = 2.0 g → 1 small square = 0.2 g.

Points to plot (tolerance is within ±½ small square):

• (0, 20.2) – already plotted
• (60, 22.0) – 6 small squares along, on the 22.0 major grid line
• (120, 23.4) – 12 small squares along, 7 small squares above 22.0
• (180, 24.2) – 18 small squares along, 1 small square above 24.0
• (240, 24.8) – 24 small squares along, 4 small squares above 24.0
• (300, 25.2) – 30 small squares along, 6 small squares above 24.0
• (360, 25.2) – 36 small squares along, 6 small squares above 24.0

🧠 How to Draw the Line of Best Fit

• Use a sharp pencil and plot points with a neat small 'x' or dot with circle.
• Do NOT use a ruler: The data forms a curve, not a straight line!
• Draw a single, smooth, continuous curve that begins steep, gradually levels off, and plateaus horizontally from 300 s to 360 s at 25.2 g.
• Avoid "tramlines" (multiple overlapping strokes) or dot-to-dot jagged lines.

✅ Acceptable Answers (Any One)

• The increase in mass decreases over each successive 60-second interval.
• The differences in mass every 60 seconds are not equal (e.g. gives examples: +1.8 g, then +1.4 g, then +0.8 g).
• After 300 seconds, the mass stops increasing / remains constant (change is 0.0 g).

💡 Data Breakdown (Mass Added per 60 s)

• 0 s to 60 s: 22.0 − 20.2 = +1.8 g
• 60 s to 120 s: 23.4 − 22.0 = +1.4 g
• 120 s to 180 s: 24.2 − 23.4 = +0.8 g
• 180 s to 240 s: 24.8 − 24.2 = +0.6 g
• 240 s to 300 s: 25.2 − 24.8 = +0.4 g
• 300 s to 360 s: 25.2 − 25.2 = 0.0 g

Chemistry note: As copper ions (Cu²⁺) are discharged at the negative electrode, their concentration drops, slowing the rate of deposition until no more copper ions remain.

💡 Alternative Method: Scaling Factor

You can also scale up to find the mass in 1000 cm³:

1. Find scaling multiplier: 1000 cm³ ÷ 25 cm³ = 40 [1 mark]
2. Multiply mass: 5.5 g × 40 = 220 g/dm³ [2 marks]

❌ Common Calculation Pitfalls

• Forgetting unit conversion: Doing 5.5 ÷ 25 = 0.22 and stopping there (only gets 1 mark).
• Upside-down formula: Dividing volume by mass (0.025 ÷ 5.5).
• Multiplying instead of dividing by 1000: Writing 25,000 dm³. Remember, 1 dm³ is 1 litre, so 25 cm³ must be a small fraction of a dm³.

✅ Correct Answer

[✓] Hydrogen is less reactive than potassium.

Tick the first box only.

💡 Rule for the Negative Electrode (Cathode)

In an aqueous solution containing H⁺ ions and metal ions:

• If the metal is more reactive than hydrogen (e.g. K, Na, Mg), hydrogen gas (H₂) forms because the less reactive element is discharged.
• If the metal is less reactive than hydrogen (e.g. Cu, Ag), the metal forms (which is why copper deposited in 06.2!).