Demonstration of Diffusion & Osmosis using an Artificial Membrane
TLSAMP '07 Group members: • Tiffany Pewitt- HillCrest High • Alana Antoine- St.Vincent Girls’ High • Danielle Chatman - Whitehaven High • Rachel Randle- Central High • Alyasha Robinson- Hillcrest High
Theorem : • The dialysis bag containing distilled water will not change significantly in weight unlike the 1.0M and 0.6M dialysis bag containing sucrose. • All three dialysis bags will turn red after 40 minutes indicating diffusion of sodium hydroxide from outside of the dialysis bag.
Definitions Osmosisis the net movement of water, through a semi-permeable membrane from a high water concentration (dilute solution) to a lower water concentration (more concentrated solution). Diffusion: Movement of molecules from a high concentration to an area of low concentration.
When does osmosis occur? • If two solutions are separated by a partially permeable membrane and the water potential (i.e. the kinetic energy of the water molecules) of each solution is different, osmosis will occur. • All the membranes in a cell are partially permeable and allow water through by osmosis. • If there is a difference in water potential between adjacent solutions osmosis will take place, it cannot be stopped.
When Does Osmosis Occur? (2) • Water molecules pass in both directions but there is a net movement of water molecules from a higher to a lower water potential. • Only when the water potential of two adjacent solutions is the same, will osmosis stop and there will be no further net movement of water molecules. • Water will then move equally between the solutions.
Osmosis occurs within 3 types of solutions: • Hypotonic • Hypertonic • Isotonic
Hypotonic solution:The solution surrounding a cell may have a lower solute concentration (e.g. sugar molecules) and therefore a higher water potential than the cell. Water passes from the solution into the cell by osmosis. Solutions with a lower solute concentration are described as hypotonic. • Hypertonic solution: The solution surrounding a cell may have a higher solute concentration and therefore a lower water potential than the cell. Water will pass out of the cell by osmosis. Solutions with a higher solute concentration are described as hypertonic. • Isotonic solution:If the solution surrounding a cell has the same solute concentration as the cell, water will pass equally between them. There will be no net movement of water. They have the same water potential. When a solution has the same solute concentration s the cell, it is described as isotonic.
Experimental Materials: • 3 strips of dialysis tubing • 8 pieces string • graduated cylinder • 1% sucrose (15mL) • 25% sucrose (15mL) • 50% sucrose (15mL and 200mL) • balance • 3 500mL beakers
Procedure: Osmosis (Diffusion of water) across an artificial membrane • Three strips of dialysis tubing (15cm long were used in these experiments. • Bag #1: 20mL of 1.0M sucrose • Bag #2: 20mL of 0.6M sucrose • Bag #3: 20mL distilled water • In all the three bags 6 drops of Phenolphthalein baseindicatorwere added. • The open end of the bag was tied with string so that no air in the bag is left and the bag was filled enough so that it will not fold up, but not so much that the bag is stiff.
Procedure: Osmosis (Diffusion of water) across an artificial membrane (2) • Each of the three dialysis bags were immersed in three separate 500 mL beaker containing 300 ml distilled water and 20 drops of 1N NaOH. • Trim the strings on each end of the closed dialysis bags. Then weight each bag and record in given Table 1.1 • Be sure the bags are completely submerged. If they are not , add enough of the appropriate solution to submerge them. • Weigh the bags at 10 minute intervals. • Take at least 5 weights following the initial weighing. • Record times and weights in Table1.1; then graph your results.
Hypothesis Testing(1) H0: Osmosis shows no effect on the weight of the distilled water and 0.6M dialysis bags. Ha: Osmosis shows significant change on the distilled water and 0.6M dialysis bags. p-value< 0.05(significant level) Reject H0
Hypothesis Testing (2) H0: Osmosis shows no effect on the weight of the 0.6M and 1.0M dialysis bags. Ha: Osmosis shows significant change on the 0.6M and 1.0Mdialysis bags. p-value< 0.05 Reject H0
Results: • As expected from the stated hypothesis the dialysis bag with 1.0M gained the most weight followed by the bag with 0.6M. • The bag with distilled water did not changed significantly. • All three bags turned red after about 40 minutes indicating the diffusion of NaOH from outside to inside of the dialysis bag.
Conclusion: • As expected according to the hypothesis, there is no gain in weight of the dialysis bag in isotonic solution. • When the dialysis bag had the hypertonic solution there was a significant weight gain by osmosis.
Acknowledgements:A special thank you to the TLSAMP Agency that funded this program.On behalf of group 2 members I will like to say thank you to Dr. Rafique Uddin, Dr. John Harris, Dr. Valerie Chu, Dr.Rajagopolan and Dr. Muhammad Shafi for all the assistance and support they have given us to make this project a success.