Lemonade-Ed - Potassium permanganate diffusion

Lemonade-Ed

Practical: Potassium Permanganate Diffusion

Instructions

Carry out the investigation then answer the questions that follow.

Aim: To investigate how temperature affects the rate of diffusion of potassium permanganate in water.

Hypothesis: Write your own prediction on what will happen.

Variables:

Independent variable: The temperature of water.
Dependent variable: The time it takes for the colour to spread to a diameter of 3 cm.
Controlled variable:
- - Size of the potassium permanganate crystals
  - Volume of water in each petri dish
  - Type of water used (same source)
  - Size and type of petri dish
  - Position of the crystal (placed in the centre each time)
  - Depth of water
  - Same measuring method for timing and measuring diameter
  - Same environment (no stirring, shaking, or blowing across the surface)

Materials

You will need:

Potassium permanganate crystals (roughly same size each)
Water
2 x petri dishes
1 x A4 paper as a white background
Electric kettle
Ruler
Stopwatch

Method

1. Place two petri dishes on the A4 paper.
2. Fill one petri dish half way of tap water (or ice cold water), and fill the other petri dish half way of hot water.
3. Place one potassium permanganate crystal at the centre of each petri dish.
4. Observe the colour change and how the crystal begins to spread through the water.
5. Record the time it takes for the colour to spread to a diameter of 3 cm.

Questions

Remember - Key facts

Question 1: What substance are we using to show diffusion in water?

Question 2: What is the independent variable in this investigation?

Question 3: What is the dependent variable in this investigation?

Question 4: Why do we use crystals that are roughly the same size in both dishes?

Understand — Explain what is happening

Question 5: Describe what you observed in the cold water and the hot water. What was different?

Question 6: Explain why the colour spreads out from the crystal instead of staying in one place.

Question 7: In your own words, explain what diffusion means using this experiment as an example.

Apply — Use ideas in new situations

Question 8: If the crystal was placed at the side of the petri dish instead of the centre, how might the pattern of spreading change? Explain why.

Question 9: Predict what would happen if you repeated the experiment using room-temperature water. Where would its rate of spreading sit compared to hot and cold? Why?

Question 10: A student used very different-sized crystals in each dish. How might that affect their results? What should they do next time to fix this?

Analyse — Break down what affects diffusion

Question 11: List the factors in this experiment that could affect how fast the colour spreads, even if temperature is the main focus.

Question 12: Explain how temperature affects the movement of particles at the particle level.

Question 13: Why is timing the spread to exactly 3 cm better than just saying ‘until it looks mixed’?

Question 14: Compare the results for hot and cold water. What do these results tell you about the relationship between temperature and diffusion rate?

Question 15: How does what you observed in this experiment help explain processes in living cells? (You can link this to gases, nutrients, or waste movement.)

2.4 C2. Potassium permanganate diffusion - Tanya's group.mp4

Need help? Consider getting Private Tutoring or Personalised Feedback for your work from Lemonade-Ed's Mrs. Heald.

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