Objective : To study the movement of substances across a semi permeable membrane
Problem statement : What factor influences the diffusion of substances through a semi permeable membrane?
Hypothesis : The diffusion of molecules across a semi permeable membrane is based on the size of the molecule
a) Manipulated : Size of solute molecules
b) Responding : Colour of solution
c) Fixed : Temperature and time
Materials : Iodine solution, Benedict’s solution, 1% starch suspension, 30% glucose solution and distilled water
Apparatus : A Visking tube, cotton thread, test tubes, beaker and water bath
- Soak the Visking tube in water for 5 minutes to soften it. Open the Visking tube and tie one end of the tube with cotton thread to prevent leakage.
- Fill the Visking tube with 15ml of glucose solution and 15ml of starch suspension. Tie the other end of tube tightly with cotton thread. Record the colour of the solution
- Rinse the outer surface of Visking tube with distilled water.
- Mix 400ml of distilled water with 15ml iodine solution in a beaker. Record the colour of the solution
- Place the Visking tube in the beaker and leave it for 40 minutes.
- After 40 minutes, take the Visking tube out and put aside
- Observe and record the colour of solution in the Visking tube and in the beaker.
- Test both solutions for the presence of glucose using Benedict’s solution. Pour 2ml of each solution into separate test tube and add 1ml of Benedict’s solution. Heat the mixture in the water bath for 5 minutes and record the colour change.
|Solution in |Contents |Iodine |test |Benedict’s test |
| | |Initial colour |Final colour | |
|Visking tube |15 ml sucrose |White precipitate |Blue black |Brick red colour |