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.

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..

An indicator is a substance that changes color when in the presence of the substance it indicates. In this experiment, IKI will be used an indicator to test for the presence of starch and glucose.

Materials(5) 100 mL Beakers
10 mL 1% Glucose Solution, C6H12O6
4 Glucose Test Strips
(1) 100 mL Graduated Cylinder
4 mL 1% Iodine-Potassium Iodide, IKI
5 mL Liquid Starch, C6H10O5
3 Pipettes
4 Rubber Bands (Small; contain latex, handle with gloves on if allergic)
*Stopwatch
*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.  
  
 
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.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.

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.
    1. Dip one of the glucose test strips into the two mL of glucose/starch solution in the third 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.
    2. Use a pipette to transfer approximately 0.5 mL of IKI to into the two mL of glucose/starch solution in the third 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.
    1. 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.
    2. 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.

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.

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