ZIMSEC O Level Combined Science Notes:Diffusion and Osmosis experiments
Aim: Create a membrane model for molecules and their movement.
Visking tubing/egg membrane, string, beaker, 20% sugar solution, weighing balance, water.
Using the Visking tubing.
- Make a cylinder using the visking tubing by tying one end securely using a string.
- Add the sugar solution until it is half full.
- Tie the remaining open end and make sure it is secure.
- Wash the bag thoroughly and dry it well.
- Weigh the bag and place it in a beaker filled with water.
- After 20 minutes remove the bag and dry it.
- Weight it and record the weight.
- Repeat the experiment by filling a visking tube with water instead of the sugar solution.
- There is an increase in the weight of the sugar solution filled visking tubing when it is weighed after being put into the water for 20 minutes.
- Explanation: Water diffuses into the visking tubing because of the differences in concentration inside and outside the tubing.
- When the experiment is repeated using a visking tubing filled with water there is no change in the weight of the visking tubing because there is equal diffusion of water moving in and out of the visking tubing since the concentration gradient between the water inside and outside the tubing is zero.
Using the egg membrane.
- Make a bag from egg membrane similar to the one shown in the diagram above.
- Support the bag in water and place the sugar solution inside the bag until it is about 1 cm below the top.
- Observe the level of the solution inside the egg membrane bag.
- The level of the sugar solution rises as water diffuses from the beaker through the membrane’s walls.
- This is because there is a higher concentration of water outside the membrane (in the beaker) than inside the egg membrane.
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