SBI4U Dialysis Investigation

Many kidney patients rely on the technology of dialysis to remove impurities from their blood. Dialysis depends on a membrane that is selectively permeable and controls the substances that pass through it. In this investigation, you will study the movement of substances through dialysis tubing. You will use chemical tests to detect the diffusion or lack thereof, of chloride ions, glucose and starch through dialysis tubing.

Problem

What substances can move through dialysis tubing along their concentration gradients?

Hypothesis

Predict which of the three substances will pass through the dialysis tubing. Justify each prediction you made. Hand these predictions in prior to testing the dialysis bath water.

Materials and Methods

A length of dialysis tubing

Two 15cm lengths of string

Scissors

50 or 100mL graduated cylinder

Two clean 250mL beakers

Pasteur pipettes

Distilled water

Balance

Paper towel or tissues

Iodine solution

Benedict’s solution

Silver nitrate solution

Stock solution containing salt, glucose and starch in water

Nine test tubes

Test-tube rack

Test-tube tongs

Labels or grease marking pencil

Hot plate

Safety goggles

CAUTION: wear safety goggles when conducting tests with solutions. Silver nitrate, Benedict’s solution, and iodine are toxic. Silver nitrate is also corrosive. Use test tube tongs to handle hot glassware. Test solutions may stain hands or clothing.

Part A: Preparation of Dialysis Bath

  1. Prepare a hot water bath. Plug in the hot plate. Add about 150mL of water to a 250mL beaker and place it on the hot plate. Set the temperature gauge on the hot plate high enough to allow the water in the beaker to boil.
  2. The dialysis tubing has been soaking in distilled water. Open it by rubbing between your thumb and forefinger as demonstrated by your teacher. Make a bag by tying one end with a length of string. Wrap the string tightly around the tubing several times before tying, to prevent leakage.
  3. Obtain the stock solution, a mixture of salt (NaCl), glucose, and starch in water. Swirl the solution to mix the contents and then transfer it to your dialysis bag until it is approximately half to two-thirds full. You will need slack in the dialysis bag.
  4. Carefully compress the open bag so the slack lays flat and air bubbles are removed. Then tie off the open end as you did in step 2.
  5. Dry the bag with tissues or paper towel and trim off excess thread.
  6. Mass the bag on the balance to the nearest tenth of a gram. Record this initial mass (mi) in Table 1.
  7. Add approximately 150mL of distilled water (dH2O) to a second, clean 250mL beaker and immerse the dialysis-tubing bag in the distilled water.
  8. Put your group name on the beaker and set it aside until tomorrow.

Part B: Controls

  1. Label three test tubes as follows: S+, G+, C+. These test tubes contain the positive controls, hence the + sign. S is for salt, G is for glucose and C is for starch (carb).
  2. Measure 10mL of distilled water into each of the positive control tubes and add 10 drops of stock solution to each tube. Place the tubes in the test tube rack.
  3. Observe and record the initial colour of the solution in the S+ tube in Table 2. Then add 5 drops of silver nitrate solution to the S+ tube. Shake the tube gently to mix the contents. Observe and record the final colour of the solution in Table 2.
  4. Observe and record the initial colour of the solution in the G+ tube in Table 2. Then add 15 drops of Benedict’s solution to the G+ tube. Shake the tube gently. Using test tube tongs, place the tube in the boiling water bath for 2-5 minutes. Using tongs, remove the test tube from the boiling water bath and place it in the test tube rack. Observe and record the final colour of the solution in Table 2.
  5. Observe and record the initial colour of the solution in the C+ tube in Table 2. Then add 5 drops of iodine solution to C+ tube. Shake the tube gently and observe and record the final colour of the solution in Table 2.
  6. Keep the tubes in the test tube rack.
  7. Label three new test tubes as follows: S-, G- and C-.
  8. Repeat steps 10-14, with the S-, G- and C-, except DO NOT put stock solution in these. Instead, add distilled water only. These are negative controls.

Part C: Testing for Diffusion and Osmosis

  1. Hand in your predictions.
  2. Label three new test tubes as follows: SDB, GDB, and CDB. Repeat steps 10-14 using 10mL of water from your Dialysis Bath (DB).
  3. Remove your dialysis-tubing bag from the dialysis bath and dry and mass it as in steps 5-6. Record the final mass(mf) in Table 1.
  4. Complete the calculation of percent change in mass and record the result in Table 1.

Results

TABLE 1: Change in Mass of Dialysis-Tubing Bag

mi
(g) / mf
(g) / m = mf-mi
(g) / m/mi x 100%

TABLE 2: Diffusion Test Results

Indicator Solution / Initial Colour / Final Colour / Result (+ or -)
Sodium Chloride
Stock solution / Silver nitrate
dH2O
Dialysis Bath Water
Glucose
Stock solution / Benedict’s solution
dH2O
Dialysis Bath Water
Starch
Stock solution /
Iodine
dH2O
Dialysis Bath Water

Discussion

  1. Compare the actual results with the results you predicted. Explain why you think the result occurred for each substance.
  2. After the dialysis bag has been in the distilled water bath overnight is it sitting in an isotonic, hypertonic or hypotonic solution? Explain and justify based on your knowledge as well as the mass data collected. Include diagrams in your response. Be precise here!
  3. What was the purpose of the control test tubes? Distinguish between positive and negative controls.
  4. The silver nitrate test shows the presence of chloride ions. If your experimental test gave a positive result for chloride ions, are there any other substances that you would expect to be present in the dialysis bath water? Explain.
  5. If you left the dialysis-tubing bag in the beaker indefinitely, would you expect the mass to increase indefinitely? Explain.

Making Connections

  1. Why is selective permeability of the cell membrane important to humans? Describe a specific example of osmosis, diffusion, and selective permeability that occurs in humans.
  2. When people suffer from kidney failure they must go on dialysis. Explain what is involved with being on dialysis. If they didn’t go on dialysis, what would happen to the patient and why would this occur?

Cite your sources using in-text and end-of-text APA citation.

SBI4U Dialysis Investigation Rubric

Criteria / Level 4 / Level 3 / Level 2 / Level 1
Thinking/Inquiry
Use of critical/creative thinking processes, skills, and strategies (e.g., analysing, performing and recording, gathering evidence and data, interpreting, problem solving, evaluating, forming and justifying conclusions on the basis of evidence and research) / Uses critical/ creative thinking processes, skills, and strategies with a high degree of effectiveness / Uses critical/ creative thinking processes, skills, and strategies with considerable effectiveness / Uses critical/ creative thinking processes, skills, and strategies with moderate effectiveness / Uses critical/ creative thinking processes, skills, and strategies with limited effectiveness
Communication
Expression and organization of ideas and information (e.g., clear expression, logical organization) in written forms (e.g., proper citation) / Transfers knowledge and skills to unfamiliar contexts with a high degree effectiveness / Transfers knowledge and skills to unfamiliar contexts with considerable effectiveness / Transfers knowledge and skills to unfamiliar contexts with moderate effectiveness / Transfers knowledge and skills to unfamiliar contexts with limited effectiveness
Application
Transfer of knowledge and
skills to unfamiliar contexts
(e.g., membranes in human
cells, human experience of dialysis) / Expresses and organizes ideas and information with a high degree of effectiveness / Expresses and organizes ideas and information with considerable effectiveness / Expresses and organizes ideas and information with moderate effectiveness / Expresses and organizes ideas and information with limited effectiveness