Diffusion and Osmosis

1. Diffusion and Osmosis

2. Dissolving KMnO4 crystal Diffusion • Particles in a liquid or gas spread out… • … from regions of high concentration… • … to regions of low concentration… • …until the particles are evenly spread out.

3. High concentration gradient Fast rate of diffusion Low concentration gradient Slow rate of diffusion • 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

4. Diffusion occurs because the particles in gases and liquids are moving.

5. Free moving water molecules Sugar molecules in sugar lump Dissolving substances in water • The molecules in liquid water are constantly moving • When water molecules bump into particles of a soluble substance, they stick to them

6. When the water molecules move away… … they carry particles of the solute with them

7. Solute molecule Free water molecules • Adding a solute to water reduces the amount of free water molecules

8. Partially permeable membrane • Generally, small particles can pass through… …but large particles cannot Partially-Permeable Membranes • A partially-permeable membrane will allow certain molecules to pass through it, but not others.

9. Partially-permeable membrane Water-solute particle is too large to pass through membrane More free water molecules on this side of membrane Free water molecules diffuse in this direction

10. Osmosis • Osmosis is the diffusion of free water molecules… • … from a region of high concentration of free water molecules… • … to a region of low concentration of free water molecules… • …across a partially-permeable membrane… • …until they are evenly spread out.