Experiment 2 Diffusion Concentration Gradients and Membrane Permeability In this experiment you will dialyze a solution of glucose and starch to observe The directional movement of glucose and starch The effect of a selectively permeable membrane on the diffusion of these molecules An indicator is a substance that changes color when in the presence of the substance it indicates You will be using an indicator to test for the presence of starch and glucose Materials 10 mL Glucose Solution CH12O6 Molecular weight 180 g mole 1 Starch Solution C6H10O5 Molecular weight 15 000 g mole 1 Iodine Potassium Iodide IKI 4 Glucose Test Strips 5 100 mL Beakers 4 Small Rubber Bands 3 Pipettes Stopwatch 100 mL Graduated Cylinder Water Scissors 15 0 cm Dialysis Tubing You must provide Be sure to measure and cut only the length you need for this experiment Reserve the remainder for later experiments Note Dialysis tubing can be rinsed and used again if you make a mistake Dialysis tubing must be soaked in water before you will be able to open it up to create the dialysis bag Follow the directions for the experiment beginning with soaking the tubing in a beaker of water Then place the dialysis tubing between your thumb and forefinger and rub the two digits together in a shearing manner This should open up the tube so you can fill it with the different solutions Attention Do not allow the open end of the dialysis tubing to fall into the beaker If it does remove the tube and rinse thoroughly with water before refilling with a starch glucose solution and replacing it in the beaker 2013 eScience Labs LLC All Rights Reserved Procedure 1 Measure and pour 50 mL of water into a 100 mL beaker Cut a piece of dialysis tubing 15 0 cm long Submerge the dialysis tubing in the water for at least 10 minutes 2 Measure and pour 82 mL water into a second 100 mL beaker This is the beaker you will put the filled dialysis bag into in Step 9 3 While the dialysis bag is still soaking make the glucose sucrose mixture Use a graduated pipette to add five mL of glucose solution to a third beaker and label it Dialysis bag solution Use a different graduated pipette to add five mL of starch solution to the same beaker Mix by pipetting the solution up and down the pipette six times 4 Using the same pipette that you used to mix the dialysis bag solution remove two mL of that solution and place it in a clean beaker This sample will serve as your positive control for glucose and starch a Dip one of the glucose test strips into the two mL of glucose starch solution in the beaker After one minute has passed record the final color of the glucose test strip in Table 3 This is your positive control for glucose b Use a pipette to transfer approximately 0 5 mL of IKI to into the two mL of glucose starch solution in the beaker After one minute has passed record the final color of the glucose starch solution in the beaker in Table 3 This is your positive control for starch 5 Using a clean pipette remove two mL of water from the 82 mL of water you placed in a beaker in Step 2 and place it in a clean beaker This sample will serve as your negative control for glucose and starch a Dip one of the glucose test strips into the two mL of water in the beaker After one minute has passed record the final color of the glucose test strip in Table 3 This is your negative control for glucose b Use a pipette to transfer approximately 0 5 mL of IKI to into the two mL of water in the beaker After one minute has passed record the final color of the water in the beaker in Table 3 This is your negative control for starch Note The color results of these controls determine the indicator reagent key You must use these results to interpret the rest of your results 2013 eScience Labs LLC All Rights Reserved 6 After at least 10 minutes have passed remove the dialysis tube and close one end by folding over 3 0 cm of one end bottom Fold it again and secure with a rubber band use two rubber bands if necessary 7 Make sure the closed end will not allow a solution to leak out You can test this by drying off the outside of the dialysis bag with a cloth or paper towel adding a small amount of water to the bag and examining the rubber band seal for leakage Be sure to remove the water from the inside of the bag before continuing 8 Using the same pipette which was used to mix the solution in Step 3 transfer eight mL of the solution from the Dialysis Bag Solution beaker to the prepared dialysis bag 9 Place the filled dialysis tube in beaker filled with 80 mL of water with the open end draped over the edge of the beaker as shown in Figure 3 Figure 3 Step 9 reference 10 Allow the solution to sit for 60 minutes Clean and dry all materials except the beaker with the dialysis bag 11 After the solution has diffused for 60 minutes remove the dialysis tube from the beaker and empty the contents into a clean dry beaker Label it dialysis bag solution 12 Test the dialysis bag solution for the presence of glucose and starch Test for the presence of glucose by dipping one glucose test strip into the dialysis bag directly Again wait one minute before reading the results of the test strips Record your results for the presence of glucose and starch in Table 4 Test for the presence of starch by adding two mL IKI Record the final color in Table 4 after one minute has passed 13 Test the solution in the beaker for glucose and starch Use a pipette to transfer eight mL of the solution in the beaker to a clean beaker Test for the presence of glucose by dipping one glucose test strip into the beaker Wait one minute before reading the results of the test strip and record the results in Table 4 Add two mL of IKI to the beaker water and record the final color of the beaker solution in Table 4 Table 3 Indicator Reagent Data 2013 eScience Labs LLC All Rights Reserved Starch Glucose Positive Negative Control Color Control Color Indicator Starch Positive Control Color Glucose Negative Control Color IKI Solution Black Brown n a n a Glucose Test Strip n a n a Green yellow Table 4 Diffusion of Starch and Glucose Over Time Indicator Dialysis Bag After 1 Hour Beaker Water After 1 Hour IKI Solution Black Brown Glucose Test Strip Green Green Post Lab Questions 1 Why is it necessary to have positive and negative controls in this experiment This allows you to determine if starch and glucose were found in the experimental beakers or not 2 Draw a diagram of …