Diffusion is the movement of a substance down the concentration gradient; moving from a higher concentration region to a lower concentration. Using a bag made up of a semi-permeable dialysis membrane, the first experiment focuses on the process of diffusion. A solution of glucose and starch is placed inside the dialysis bag. With the help of test tape, the presence of glucose is established. Later, a solution of iodine potassium iodide (IKI) is added to distilled water filled in a beaker which will turn the water brownish-yellow. The solution is tested for glucose, which shows a negative result establishing its absence. Next tie up the dialysis bag which has a clear fluid and place it in the beaker. After waiting for thirty minutes the observations are recorded. The results show that the clear fluid inside the bag turns bluish-black. A retest of the solution in the beaker proves the presence of glucose. These results show that iodine from the external solution moved across the member into the starch fluid whereas glucose diffused across into the beaker. The starch particles are too large to travel and since the outside solution did not change color, we can prove that starch did not move across the membrane.
The second part of the lab demonstrates the process of osmosis which is the diffusion of water down its concentration gradient; from a region of higher water concentration to lower concentration. Make six dialysis bags filling one with distilled water and the rest with sucrose solutions of different concentrations up to 1 molar sucrose and weigh them. Since sucrose cannot cross the dialysis membrane, the bags are placed in a beaker filled with two-thirds of water. After thirty minutes the bags are weighed again. The results show a greater change in mass for bags with higher molarity of sucrose. This is because more water entered these bags due to a high concentration of sucrose.
Diffusion and Osmosis. (n.d.). Retrieved from https://youtu.be/ZRJal8HmKPk