Diffusion and Osmosis Experiment
7.1 Experiment: Rate of Diffusion of Solutes
In the initial set up of this experiment I had 2 sets of 3 screw-cap test tubes that had each been half-filled with 5% gelatin and 1-mL of the correct dye (either potassium dichromate, aniline blue, or Janus green) in each of the test tubes. I labeled the 3 test tubes of set 1 with which die they contained and marked them “5 ˚C”. Then with the other set I did the same exact thing, except I labeled these test tubes “Room Temperature”. I then placed set 1 of the test tubes in a 5˚ C refrigerator, while I kept set 2 at room temperature for a certain amount of time. I made sure to record the time I began the experiment in my lab manual. To begin, I removed set 1 from the refrigerator and compared the distance the dye had diffused in each of the 3 test tubes with the corresponding test tubes of set 2 that had been kept at room temperature. Next, I held each tube vertically in front of a white sheet of paper, and then used a metric meter to measure how far the dye had diffused from the gelatin’s surface (in millimeters). I then recorded each of these distances in my lab manual. I repeated this step for each of the test tubes in both set 1 and set 2 and recorded my results. Then, using my results, I calculated the rate of diffusion for each dye by using this formula: rate of diffusion = distance/ elapsed time (hours). Each of these calculations was then also recorded in my lab manual. I made sure I noted the time the experiment started, ended, and the total elapsed time in hours in my lab manual as well.
7.2 Experiment: Osmosis
I worked in a group of 4 to complete this experiment. First off I took the four sections of 15-cm long dialysis tubing that had been presoaked in dH2O and folded over one end of each tube (I found that twisting works well too) and tightly tied one of the 8 10-cm pieces of string (or waxed dental floss) that I cut with scissors around it to close off one end of the tubing. Then, I attached a string tag labeled with the appropriate number (1-4) to the tied end of the bag using the same string. Next, I used a graduated cylinder to measure out 10-mL of dH2O for bag 1, 10-mL of 15% sucrose for bag 2, 10-mL of 30% sucrose for bag 3 and 10-mL of dH2O for bag 4. I placed the open end of the bag over the stem of the funnel apparatus set on a ring stand and poured the measured solutions from the graduated cylinder through the funnel and into each bag. As each bag was filled with the correct solution, I folded (or twisted) the end of the bag, making sure to leave a small amount of air for the bag to expand if needed and tied off the end of the bag with another piece of string (or dental floss). After this I labeled each of the four 400-mL beakers with a china marker (1-4). I added 200-mL of dH20 to the beakers labeled #1-3 and add 200-mL of the 30% sucrose solution to beaker #4. I placed the bags labeled 1-3 in the corresponding numbered beakers and placed bag 4 in beaker #4 containing the 30% sucrose solution. After 15 minutes passed, I removed each bag from the beaker, dried off the excess liquid with a paper towel, and weighed each bag on the balance. I recorded the weights in my lab manual. Then, I repeated these last steps for the next three 15 min. intervals at 30 min., 45 min., and 60 min. from time zero.
7.3 Experiment: Selective Permeability of Membranes
For this experiment I took a 25-cm section of dialysis tubing that has been soaked in dH2O and folded over (or twisted) one end of the tubing and tied it tightly to make it leak-proof with one of the 10-cm pieces of string (or dental floss) that I cut with scissors. I then slipped the end of the bag over the stem of the funnel that was held in place in the ring stand and I filled the bag approximately half full with 25-mL of a solution of 1% soluble starch in 1% sodium sulfate (NA2SO4) that I measured out in a 25-mL graduated cylinder. I removed the...
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