2.4 Diffusion And Osmosis

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2.4 Diffusion And Osmosis

  1. 1. Diffusion and Osmosis
  2. 2. Diffusion <ul><li>Particles in a liquid or gas spread out… </li></ul><ul><li>… from regions of high concentration… </li></ul><ul><li>… to regions of low concentration… </li></ul><ul><li>… until the particles are evenly spread out. </li></ul>Dissolving KMnO 4 crystal
  3. 3. <ul><li>The difference between the regions of high concentration and low concentration is called the concentration gradient </li></ul><ul><li>The steeper the concentration gradient, the faster diffusion takes place </li></ul>High concentration gradient Fast rate of diffusion Low concentration gradient Slow rate of diffusion
  4. 4. <ul><li>Diffusion occurs because the particles in gases and liquids are moving. </li></ul>
  5. 5. Dissolving substances in water <ul><li>The molecules in liquid water are constantly moving </li></ul><ul><li>When water molecules bump into particles of a soluble substance, they stick to them </li></ul>Free moving water molecules Sugar molecules in sugar lump
  6. 6. <ul><li>When the water molecules move away… </li></ul>… they carry particles of the solute with them
  7. 7. <ul><li>Adding a solute to water reduces the amount of free water molecules </li></ul>Free water molecules Solute molecule
  8. 8. Partially-Permeable Membranes <ul><li>A partially-permeable membrane will allow certain molecules to pass through it, but not others. </li></ul><ul><li>Generally, small particles can pass through… </li></ul>Partially permeable membrane … but large particles cannot
  9. 9. More free water molecules on this side of membrane Free water molecules diffuse in this direction Partially-permeable membrane Water-solute particle is too large to pass through membrane
  10. 10. Osmosis <ul><li>Osmosis is the diffusion of free water molecules… </li></ul><ul><li>… from a region of high concentration of free water molecules… </li></ul><ul><li>… to a region of low concentration of free water molecules… </li></ul><ul><li>… across a partially-permeable membrane … </li></ul><ul><li>… until they are evenly spread out. </li></ul>

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