Experiment Design Question (Copy)

In ATP Paper 6, experiment design questions are worth up to 6 marks and are often the highest-weighted individual question. You are expected to design a valid scientific experiment, often in response to a short hypothesis or observation.

The examiner wants to assess whether you understand:

• How to plan a fair and accurate experiment
• How to control variables
• How to describe realistic methods
• How to collect valid data
• How to ensure safety

🔍 1. What These Questions Look Like

Typical question prompts:

• “Describe how you would carry out an experiment to investigate…”
• “Design an experiment to find out…”
• “Plan an experiment to test the hypothesis…”
• “You are provided with… Explain how you would use these to…”

You may be asked to:

• Design the entire experiment from scratch
• Modify a method
• Suggest improvements
• Identify variables or sources of error

⚙️ 2. Full Structure for a 6-Mark Experiment Design Answer

Use the following structured template to score full marks:

A. Variables (3 types)

• Independent variable: what you change
• Dependent variable: what you measure
• Control variables: what you keep the same (at least two)

B. Method (Step-by-Step Procedure)

• Apparatus to be used
• How you will change the independent variable
• How you will measure the dependent variable
• Include exact measurements (e.g. 25 cm³, 5 min, 0.1 mol/dm³)
• Specify how many trials or repeats

C. Data Collection

• What to record and how
• Table headings
• Graph idea (if applicable)

D. Safety Precautions

• Mention if handling:
  • Acids or alkalis (wear goggles)
  • Heat (use tongs or heatproof mats)
  • Toxic/corrosive substances (wear gloves)

🧪 3. Example Question + Full Sample Answer

Q: Design an experiment to investigate how the concentration of hydrochloric acid affects the rate of reaction with magnesium ribbon.

✅ Sample Full-Mark Answer:

Variables:

• Independent: Concentration of HCl (e.g., 0.5, 1.0, 1.5 mol/dm³)
• Dependent: Time taken to produce a fixed volume of hydrogen gas
• Control: Temperature, volume of acid, length/mass of magnesium, same apparatus

Method:

1. Add 25 cm³ of 0.5 mol/dm³ HCl to a conical flask using a measuring cylinder
2. Add a strip of magnesium ribbon of fixed length (e.g., 3 cm)
3. Immediately start a stopwatch
4. Record the time taken to collect 50 cm³ of hydrogen in an inverted measuring cylinder
5. Repeat steps with 1.0 mol/dm³ and 1.5 mol/dm³ HCl
6. Repeat each concentration 3 times and take an average

Data Collection:

• Record volume of gas against time for each concentration
• Table:
  

  Concentration (mol/dm³)	Time for 50 cm³ gas (s)
  0.5
  1.0
  1.5

• Plot graph of concentration vs rate (1/time)

Safety:

• Wear goggles due to corrosive acid
• Use tongs to handle magnesium if heated
• Wash hands after handling chemicals

🧮 4. Examples of Common Experiment Design Topics

⚠️ 5. Common Mistakes in Experiment Design Questions

🧠 6. Tips to Score Full Marks Every Time

• Memorize the A–B–C–S structure:
  • Apparatus & variables
  • Basic steps (method)
  • Collect data (table + graph idea)
  • Safety
• Practice at least 5 common design questions using full template
• Underline units and variables when revising for clarity
• Use a pencil and ruler when drawing any diagram
• Always read the question carefully to know what you’re being asked to investigate

📌 7. Mark Scheme Breakdown (for 6-mark design question)