dissolving KMnO4 crystal Diffusion Particles in a liquid or gas spread out… … from a region where they are at a high concentration… … to regions where they are at a low concentration… …until the particles are evenly spread out. dissolving KMnO4 crystal Click on the round rectangles to make them disappear. Clicking on the liquid in the diagram shows the effect of diffusion. Task 1 Task If someone on the other side of the room sprays some perfume explain why it takes a while before you can smell it. © www.teachitscience.co.uk 23793

Explain why particles diffuse in liquids and gases. Task 2 Explain why particles diffuse in liquids and gases. Diffusion occurs because the particles in gases and liquids are moving randomly. © www.teachitscience.co.uk 23793

higher concentration gradient Task 3 Look at the two diagrams. Which direction will diffusion take place? Which has the biggest concentration gradient? In which will diffusion take place fastest? The difference between the regions of high concentration and low concentration is called the concentration gradient. The steeper the concentration gradient, the faster diffusion takes place. higher concentration gradient fast rate of diffusion lower concentration gradient slow rate of diffusion © www.teachitscience.co.uk 23793

Teaching notes Slide 1 and 2 Click directly on the boxes to reveal the answers. Click the beaker to show effect of diffusion. Teaching suggestions Diffusion could be introduced by setting up some demonstrations: diffusion in gases – spray some perfume at the back of the classroom with students facing forwards. Ask them to raise their hands when they can smell it. diffusion in liquids – drop a potassium permanganate crystal into a beaker of water. diffusion in solids – drop a potassium permanganate crystal onto a petri dish of agar jelly. Ask the students to compare the speed of diffusion through the different states. Ask them to explain the different rates of diffusion with reference to the particle model. © www.teachitscience.co.uk 23793