How Molecules Move With Respect to Concentration Lab

Pre-Lab Questions 1. A concentration gradient affects the direction that solutes diffuse. Describe how molecules move with respect to concentration. Diffusion of solutions typically moves from areas of high concentration to areas of low concentration. 2. How does the size of a solute affect the rate of diffusion? Consider the size and shape of a molecule in your response. Solute size and diffusion rate are inversely proportional, therefore the bigger a solute molecule is, the slower it diffuses. 3. Does polarity affect the rate of diffusion? Explain your answer using scientific principles. Polarity has little effect on the diffusion rate of molecules. Polar molecules do not fuse well though the lipid core of the phospholipid bilayer of the plasma membrane. Nonpolar molecules diffuse much easier. Different types of molecules require different types of diffusion. Experiment 1: Diffusion Through A Liquid Result Tables Table 1: Rate of Diffusion in Corn Syrup Time (sec) Diffusion of Blue Dye (mm) Diffusion of Red Dye (mm) 10 6mm 10mm 20 4mm 5mm 30 3mm 2mm 40 2mm 2mm 50 1mm 3mm 60 1mm 1mm 70 0.50mm 2mm 80 0.40mm 0.50mm 90 0.40mm 1mm 100 0.40mm 0.25mm 110 0.20mm 0.50mm 120 0.10mm 0.10mm Table 2: Speed of Diffusion of Different Molecular Weight Dyes Dye Molecular Weight Total Distance Traveled (mm) Speed of Diffusion (mm/hr)* Blue Dye 793 g/mole 19mm 570mm/hr Red Dye 496 g/mole 24.35mm 730.5mm/hr *Multiply the total distance diffused by 30 to get the hourly diffusion rate. Post-Lab Questions 1. Record your hypothesis from Step 3 here. Be sure to support your hypothesis with evidence. If solutions with lower molecular weights diffuse faster, than the red dye solution should diffuse faster in the corn syrup than the blue dye solution, because it’s molecular weight is 496 g/mole while then blue dye’s is 793 g/mole. 2. Which dye diffused the fastest? The red dye diffused the fastest in the corn starch. 3. Does the rate of diffusion correspond with the molecular weight of the dye? Yes, because the red dye has a lower molecular weight, it diffused faster in the corn syrup. 4. Does the rate of diffusion change over time? Why or why not? Yes, because as the solution diffuses, it becomes less concentrated and therefore diffuses much slower. The diffusion was rapid at first for both dyes because the concentration was high, so they both spread quickly out in the non-concentrated corn syrup. 5. 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. The proportions are correct, as the red dye diffused faster and had a larger diffusion distance, but numerically, the graph below is not quite accurate. The dyes diffused much more that a millimeter each during the first 20 seconds. Experiment 2: Concentration Gradients and Membrane Permeability Result Tables Table 3: Indicator Reagent Data Indicator Starch Starch Glucose Glucose Positive Negative Positive Negative Control (Color) Control (Color) Control (Color) Control (Color) IKI Solution Dark brown Orangey caramel n/a n/a Glucose Test Strip n/a n/a Yellow Yellow Table 4: Diffusion of Starch and Glucose Over Time Indicator Dialysis Bag After 1 Hour Beaker Water After 1 Hour IKI Solution Light yellow with dark brown swirl Caramel yellow color Glucose Test Strip Yellow Yellow Post-Lab Questions 1. Why is it necessary to have positive and negative controls in this experiment? It is necessary to have positive and negative controls in this experiment because it ensures that the color results are due to the independent variable, which in this case is the contents of each solution being tested with the glucose strips and IKI solution. 2. Draw a diagram of the experimental set-up. Use arrows to depict the movement of each substance in the dialysis bag and the beaker. 3. Which substance(s) crossed the dialysis membrane? Support your response with data-based evidence. The glucose passed through the dialysis membrane. This is true based off of the leftover starch remnants in the bag after it had sat for an hour. My glucose test did not imply the presence of glucose in the solution, but from the visible starch remnants and the properties of starch and glucose, the dialysis membrane was only permeable by the glucose. 4. Which molecules remained inside of the dialysis bag? The starch molecules remained inside of the dialysis bag, because after sitting for an hour, there was a white, non liquid substance left in the bag. 5. Did all of the molecules diffuse out of the bag into the beaker? Why or why not? No, all of the molecules did not diffuse out of the bag into the beaker because there were white remnants of starch left in the bag separated from the liquid. The starch did not pass through the dialysis membrane because the starch molecules were too large. The glucose and water molecules on the other hand, were small enough.