Dialysis Diffusion Lab
Purpose/Objective:
To simulate the process of diffusion
To determine which substance(s) can diffuse through a semi-permeable membrane (dialysis tubing)
Materials:
Sugar Solution Starch Solution Glass Rod
Dialysis Tubing Pipettes (2) Test Tubes (4)
Test Tube Rack Iodine Solution String
Benedicts Solution 250 ml Beaker Hot Water Bath
Procedure:
1) Prepare the dialysis tubing as follows:
- rub ends of the tubing apart between your fingers; use a glass rod to help assist you
- twist one end of the tubing, fold it over, and tightly tie off with a piece of string
2) Fill the dialysis tubing ½ full with starch solution and ½ full with sugar solution
3) Twist the other end of the tubing, fold it over, and tightly tie off with a piece of string.
4) Rinse the dialysis bag carefully under the sink with water and then submerge in a beaker of water for 20 minutes.
5) Label your four test tubes: #1, #2, #3, #4 (make sure to use a distinguishing mark to identify yours)
6) After 20 minutes, take a pipette full of water from the beaker and add it to test tube #1.
7) To test for the presence of sugar, add 10 drops of Benedicts Solution to test tube #1 and heat it for 10 minutes in a hot water bath. Record your observations in the Data/Results Table.
8) Put another pipette full of water from the beaker into test tube #2.
9) To test for the presence of starch, add 3 drops of Iodine solution to test tube #2. Record your observations in the Data/Results Table.
10) Open the dialysis bag and put one pipette full of solution from the dialysis bag into test tube #3.
11) Add 10 drops of Benedicts Solution to test tube #3 and heat it for 10 minutes in a hot water bath. Record your observations in the Data/Results Table.
12) Put another pipette full of solution from the dialysis bag into test tube #4.
13) Add 3 drops of Iodine solution to test tube #4. Record your observations in the Data/Results Table.
14) Clean up…rinsing all materials thoroughly.
Data/Results:
Test Tube # / Substance Tested for / Location of Solution / Description of Color / Presence of Substance (+ / - )* Substance Tested for: Starch or Sugar
* Location of Solution: Beaker or Dialysis Bag
* Presence of Substance: + = positive test - = negative test
Discussion:
1) Which two substances are being tested for in this experiment?
2) Why do you rinse the dialysis bag with water before placing it into a beaker of water to soak?
3) What color did test tube #1 turn after heating? How does this compare to test tube #3? What does
this mean?
4) What color did test tube #2 turn after adding Iodine Solution? How does this compare to test tube
#4? What does this mean?
5) To which substance(s) is the dialysis tubing permeable?
6) Explain how the dialysis tubing acted like a semi-permeable membrane.
7) Explain how diffusion was demonstrated in this experiment.