3. Explain diffusion in terms of the particle model

Prior Learning: 

Revise KS2 learning by recapping on diffusion and the idea of the concentration gradient. Use the starter task to approach this. Discuss the students’ homework assignments from lesson 2; what solubility and saturation points did they discover? 

Starter

Begin by asking students if they have ever noticed how perfume spreads out in a room. Explain that this is an example of diffusion, which is the movement of particles from an area of high concentration to an area of low concentration. Show a few examples of diffusion in everyday life, such as how food colouring spreads in water or how oxygen diffuses into our lungs. Introduce the concept of diffusion in chemistry and explain that it is a fundamental process that is important in many chemical reactions.

Main Teaching

Direct Instruction (15 minutes): 

• Explain that diffusion occurs when particles move from an area where they are more concentrated to an area where they are less concentrated. This can happen in liquids, gases, and even solids.
• Explain that diffusion can be affected by several factors such as temperature, pressure, and concentration.
• Use diagrams and pictures to help students visualise the concept of diffusion.

Guided Practice (15 minutes):

• Divide students into groups of 2 or 3 and give them each a glass beaker filled with water, a dropper, and a few drops of food colouring.
• Ask them to observe how the food colouring diffuses into the water and record their observations.
• Have students measure the time taken for the food colouring to fully diffuse into the water using timers.

Independent Practice (15 minutes):

• Provide each student with a microscope slide, iodine solution, and starch solution.
• Ask them to place a drop of starch solution on one side of the slide and a drop of iodine solution on the other side.
• Observe under microscope and record observations.

Career Film: Elizabeth is a Manufacturing Engineer and Purchasing at Rolls-Royce. Elizabeth and her colleagues talk about their careers in the nuclear industry.

Career Film: PhD student Alice Godden discusses her career in scientific research.

Expert Film: Perfumer Diane Viall as she explains how she makes perfume. 

Mission Assignment

Particle Party!

Students should take on the role of an individual particle. All students should begin in the corner of one room. When they are told 'go' they are to move as far apart from each other as possible. 

Once they have done this, they should use their handout to draw what happened in terms of the particle model, explain what the model represented and how diffusion works. 

Use the support and challenge tasks to provide differentiated activities for this lesson.

Differentiated tasks (Support/Challenge)

Support:

Task: Observing Diffusion

Materials:

• 2 clear plastic cups
• Food colouring
• Water
• A stopwatch or timer

Procedure:

1. Fill one of the plastic cups with water, and add a few drops of food colouring to the water. Stir the water gently to distribute the food colouring evenly.
2. Fill the second plastic cup with plain water.
3. Pour the water with food colouring from the first cup into the second cup. Make sure to pour slowly and carefully so as not to mix the two waters too much.
4. Start the timer and observe what happens.
5. Every minute, take a look at the two cups and record what you see in a table, including the time and the appearance of the water in each cup.
6. Repeat the observation for 5-10 minutes, or until the water in the second cup has become fully mixed with the food colouring.

Challenge: Provide an extra task on the temperature dependence of diffusion. Students will be able to understand the concept of diffusion and observe it in action through a hands-on investigation.

Materials:

• Glass jars or beakers
• Food colouring
• Water
• Droppers
• Timers

Procedure:

1. In groups of 2 or 3,give each group a glass jar or beaker filled with water of different temperature.
2. Provide each group with a dropper and a few drops of food colouring.
3. Ask students to use the dropper to add a few drops of food colouring to the water in the jar or beaker.
4. Have students start a timer and observe how the food colouring diffuses into the water. They should make note of the time it takes for the food colouring to fully diffuse into the water.
5. Repeat the process with different amounts of food colouring and different temperatures of water to observe how these factors affect the rate of diffusion.
6. After finishing, students should compare and discuss their results as a class.

Collect students' observations and have them present their findings to the class. Use their observations and explanations to assess their understanding of the concept of diffusion and how factors such as temperature and concentration can affect it.

Extension: Ask students to research about diffusion in gases and liquids and to prepare a small presentation to share with the class.

Safety: Remind students to handle droppers carefully and to avoid contact with eyes or mouth.