osmosis

• Osmosis


  The movement of water molecules from an area of high water concentration to an area of low water concentration across a partially permeable membrane
• Osmosis is a special case of diffusion, which only occurs with water molecules moving in and out of cells
• Dilute solution


  Has a large amount of water molecules and a small amount of solute (e.g. glucose or salt)
• Concentrated solution


  Has a small amount of water molecules and a lot of solute
• Osmosis


  The movement of water molecules from a dilute to a concentrated solution across a partially permeable membrane
• Required Practical 3 - Investigating the effect of concentration on osmosis

  1. Cut 3 tubes of potato to the same size

  2. Gently blot each tube to remove any excess water

  3. Weigh the mass of each tube

  4. Add 50cm3 concentrated sugar solution to tube A

  5. Add 50cm3 dilute sugar solution to tube B

  6. Add 50cm3 of pure water to tube C

  7. Add a potato tube to each test tube and leave for 45 minutes

  8. Remove the potato from the test tube, gently blot each tube and re-weigh the potato
• Tube A


  • Concentrated sugar solution
• Tube B


  • Dilute sugar solution
• Tube C


  • Pure Water
• In the concentrated solution, the potato tube lost mass because water moved by osmosis from the potato into the surrounding solution. This was because the solution was more concentrated than the potato.
• In pure water the potato gained mass because water moved into the potato as it was more concentrated than the solution.