IB 1108 L06 Diffusion

Pre-Lab Questions A concentration gradient affects the direction that solutes diffuse. Describe how molecules move with respect to concentration. Solute molecules move from a region of higher concentration, which is called diffusion. How does the size of a solute affect the rate of diffusion? Consider the size and shape of a molecule in your response. The size of the solute molecule and the rate of diffusion are inversely proportional. Which means that the bigger the size of the solute, the slower the rate of diffusion will be. Does polarity affect the rate of diffusion? Explain your answer using scientific principles. Polarity of solute has a negative effect on diffusion of molecular solvents like water and other solutions. Experiment 1: Diffusion Through A Liquid Result Tables Table 1: Rate of Diffusion in Corn Syrup Time (sec) Blue Dye Red Dye 10 7mm 14mm 20 10mm 15mm 30 11mm 17mm 40 12mm 18mm 50 12mm 20mm 60 13mm 21mm 70 15mm 23mm 80 16mm 25mm 90 16mm 25mm 100 16mm 26mm 110 17mm 26mm 120 17mm 26mm Table 2: Speed of Diffusion of Different Molecular Weight Dyes Dye Molecular Weight Total Distance Traveled (mm) Speed of Diffusion (mm/hr.)* Blue Dye 793g/m 250mm 7500mm/hr Red Dye 496g/m 156mm 4680mm/hr *Multiply the total distance diffused by 30 to get the hourly diffusion rate. Post-Lab Questions Record your hypothesis from Step 3 here. Be sure to support your hypothesis with evidence. The temperature of the water increases then the rate of diffusion will increase. If the temperature of the water decrease, then the rate of diffusion will decrease. Which dye diffused the fastest? The red dye diffused faster Does the rate of diffusion correspond with the molecular weight of the dye? Yes, it did Does the rate of diffusion change over time? Why or why not? Yes as the solution will then reach equilibrium, the diffusion rate will decrease Examine the graph below. Does it match the data you recorded in Table 2? Explain why or why not. Submit your own plot if necessary. No It did not match and the reason it didn’t is because the time and distance of the diffusion was wrong. Experiment 2: Concentration Gradients and Membrane Permeability Result Tables Table 3: Indicator Reagent Data Indicator Starch Positive Control (Color) Starch Negative Control (Color) Glucose Positive Control (Color) Glucose Negative Control (Color) IKI Solution Yellow Orange n/a n/a Glucose Test Strip n/a n/a No color change(yellow) No color change (yellow) Table 4: Diffusion of Starch and Glucose Over Time Indicator Dialysis Bag After 1 Hour Beaker Water After 1 Hour IKI Solution Orange/brown Orange/brown Glucose Test Strip green green Post-Lab Questions Why is it necessary to have positive and negative controls in this experiment? -we use the positive and negative controls to know that there is no trace of glucose. Draw a diagram of the experimental set-up. Use arrows to depict the movement of each substance in the dialysis bag and the beaker. Which substance(s) crossed the dialysis membrane? Support your response with data-based evidence. The glucose was the one that crossed the dialysis membrane because the glucose showed there was glucose present. Which molecules remained inside of the dialysis bag? Starch Did all of the molecules diffuse out of the bag into the beaker? Why or why not? No because when tested for starch the test was negative