How did you determine if diffusion and/or osmosis occurred in the dialysis experiment?
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Lab Activities: Osmosis and Diffusion through Dialysis Tubing (Experiment) In this first exercise, we are testing whether diffusion and osmosis can occur through a membrane and if so, which molecules are able to pass through. Dialysis tubing is an artificial membrane with pore sizes that allow molecules with molecular weights of less than 1000 to pass through. Thinking about the molecular weights of our test molecules: water (18), NaCl (58.5), Na2SO4 (142), and starch and protein (730,000), which molecules might diffuse through the dialysis membrane? Do you think osmosis will occur simultaneously? Please write your hypothesis for this exercise before you begin. Materials (per group of 4-5): - 6-8 inch piece of dialysis tubing (your instructor will cut this for you) - medium beaker (250-500mL) or finger bowl - small beaker (50 mL) - 16 test tubes in a test tube rack - test reagents (droppers of AgNO2, BaCl2, Biuret, and I2KI) Procedure: 1. Start of Experiment: - Soak the dialysis tubing in water for a few minutes until soft. - Gently manipulate the tubing to fully open. - Tie off one end of the tubing. You can also tie a piece of string below the knot for insurance. - Add the protein/NaCl solution (roughly 12-15 ml, no need to measure) into the bag until it is about 2/3 full. DO NOT COMPLETELY FILL THE BAG. - Tie off the other end of the tubing again using string, if you wish. Make sure there is not an air bubble in the bag large enough to cause the bag to float. - When tying the bag, make sure the bag is not taut. The bag must be slack enough to expand if necessary. - Carefully rinse off the bag with tap water to remove any contamination. - Lightly blot the bag dry and weigh it to the nearest 0.1. Record this number. - Place the bag in a clean, dry medium beaker. - Pour enough of the starch/Na2SO4 solution to completely cover the bag. You do not need to fill the beaker all the way to the top, just cover the bag. 2. During Experiment: - Every 20 minutes or so, gently swirl the beaker to mix the solution surrounding the bag.
Sri K.
Virtual Dialysis Simulation 7. Did iodine diffuse into the dialysis tube? What visual evidence do you base your answer on? Yes, iodine diffused into the dialysis tube because just only the tubing bag looks dark purple. 8. Did the starch diffuse out of the dialysis tube into the beaker? How do you know? What indicator (colored molecule) helped you determine this? No, the starch didn't diffuse out of the dialysis tube into the beaker because if both iodine and starch was able to diffuse across the dialysis tube, then they would make both side turning to dark purple. 9. Did glucose diffuse out of the dialysis tube? How did you come to this conclusion? Yes, glucose diffused out of the dialysis tube because diffusion occurred base on molecular size. 10. For any of the molecules in the previous questions that did move, what was the driving force and type of transport that they needed to move?
Yanni D.
Diffusion and Osmosis (Dialysis Bag Test Glucose Solution)
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