Osmosis and Diffusion

Objectives:To determine if a membrane is permeable to water, starch, glucose and iodine.

Figure 1: Diagram of Experimental Setup

(draw diagram from board in class)

Hypothesis:

Data:

Data Table 1: Mass of dialysis tubing

BEFORE / AFTER / +/-DIFFERENCE
Mass (g.)

Data Table 2: Tests for Substances

STARCH / GLUCOSE / IODINE
Filling solution ( in dialysis tube)
(before)
Filling solution
(in dialysis tube)
(after)
Water in beaker (before)
Water in beaker (after)

Figure 2: Stem and Leaf of Mass Change

Data Table 3: Summary Data Table of Mass Change

Figure 3: Box Plot of Mass Change

Analysis Questions:

  1. Which part of the cell does the dialysis tubing represent?
  2. Explain what the color change inside the dialysis tube indicated. Based on these findings what diffused across the membrane?
  3. Did the color of the beaker water change to indicate the presence of starch? What can be stated about the permeability of the “membrane” to starch?
  4. What evidence would suggest that the “membrane” is permeable to glucose?
  5. Give a hypothesis as to why starch did not diffuse into the beaker of water.
  6. Based on the class data involving the mass of the filled dialysis tube before and after, make a statement describing why there was a change in mass. Is this an example of osmosis or diffusion?

Results: (state whether each substance permeated the tubing)

Conclusions: (Discuss the objective and your hypothesis. Support with data. Discuss each substance, show evidence, explain why each was or was not able to pass through the “membrane”. Discuss any sources of error.)

OSMOSIS AND DIFFUSION EXPERIMENT PROCEDURE

Filling Solution = solution used to fill dialysis tube

Results of Tests for Substances

Substance being tested / Positive (+) / Negative (-)
Starch / Turns black when in contact with iodine; Looks clear or cloudy in water / No black color seen
Iodine / Black when in contact with starch; rusty orange when in plain water / Clear water
Glucose / Test strip turns green or brown / Test strip stays blue

Day 1:

  1. Tie one end of dialysis tube tightly
  1. Fill tube with 30 ml of filling solution
  1. Make sure to release any air in tubing, then tie off open end.
  1. Rinse tubing with water and dry.
  1. Mass the filled dialysis tube using the digital balance.
  1. Record mass in data table.
  1. Fill a 250-ml beaker with enough distilled water to cover the dialysis tube.
  1. Add 2 dropperfulls of Lugol’s iodine to the water in the beaker
  1. Place label with your names and period on beaker

10.Record “water in beaker” data for before. (Is there glucose in the beaker? Is there iodine in the beaker? Is there starch in the beaker?)

  1. Set beaker in designated area until tomorrow

Day 2:

  1. Test the water in the beaker for glucose using a glucose test strip.
  1. Examine the water in the beaker for the presence of starch and iodine. Record results in data table.
  1. Pour water in beaker down the sink, rinse tubing and dry.
  1. Mass the tubing using the digital balance. Record in the data table.
  1. Rinse 250-ml beaker well
  1. Cut open tubing and pour contents into cleaned beaker
  1. Test solution from tubing for glucose. Examine solution from tubing for presence of starch and iodine. Record results in data table.
  1. Discard tubing, clean glassware and return to bin.
  1. Look at your data and THINK about what it means, then answer the analysis questions.