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Lesson 10 - Lab 3 - Exercises to Demonstrate Filtration, Diffusion and Osmosis

Student Performance Objectives
1. Demonstrate diffusion of a solid in a solid, and a gas in a gas using simple laboratory
    equipment and chemicals.
2. Demonstrate filtration utilizing simple laboratory equipment and chemicals.
3. Demonstrate osmosis utilizing simple laboratory equipment and a blood sample.

Lesson Outline
A. Diffusion (solid in a solid) Exercise: Students place several crystals of potassium
     permanganate on one side of a Petri dish and several crystals of Methylene blue on the other
     side of the same Petri dish and observe and compare the rate of movement of the crystals
     through the agar. Do this first - observe in one hour.
    1. Why does one crystal diffuse more rapidly than the other?
    2. What are the molecular weights of these crystals?
B. Diffusion (gas in a gas) Exercise: Open and pour cologne or perfume into a dish and record
     the seconds before students notice the odor. Is the principle of diffusion the same in gases
     and solids?
C. Filtration Exercise: Students prepare funnels with filter paper and pour in water with
     charcoal and CuSO4
    1. Does the charcoal pass through?
    2. Does the water and copper sulfate pass through? How do you know?
D. Osmosis Exercise: Explain the concept of freely permeable, semi-permeability (selective
     permeability), and impermeability with regard to membranes.
    1. Osmometer demonstration - observe the upward movement of water in an Osmometer
        filled with molasses and dipped in distilled water.
        a. Why does water enter into the thistle tube?
        b. How high will the water go before it stops?
    2. Blood cell hemolysis and crenation exercise: prepare 3 test tubes - one with distilled
        water, one with 0.9% NaCl, and one with 10% NaCl. Place several drops of sheep's
        blood into each tube, mix gently and hold up against a white background with a black
        a. Through which tube(s) is the line clearly visible?
        b. Through which tube(s) is the line not visible?
    c. Use microscopes to observe the blood cells in each tube.
            (1) In which tube are the blood cells normal in appearance? Explain.
            (2) In which tube are the blood cells crenated? Explain this.
            (3) In which tube are there no whole blood cells? Explain this.

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