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:
Procedure
Note: The color results of these controls determine the indicator reagent key. You must use these results to interpret the rest of your results.
Figure 4:Step 9 reference.
Table 3: Indicator Reagent Data
Indicator
Starch Positive
Control (Color)
Starch Negative
Control (Color)
Glucose Positive
Control (Color)
Glucose Negative
Control (Color)
IKI Solution
Dark Purple
Black
n/a
n/a
Glucose Test Strip
n/a
n/a
Light Green
Yellow
Table 4: Diffusion of Starch and Glucose Over Time
Indicator
Dialysis Bag After 1 Hour
Beaker Water After 1 Hour
IKI Solution
Glucose Test Strip
Purple
Post-Lab Questions
1. Why is it necessary to have positive and negative controls in this experiment?
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.
4. Which molecules remained inside of the dialysis bag?
5. Did all of the molecules diffuse out of the bag into the beaker? Why or why not?