Riley Lambertsen

Osmosis/Diffusion Lab

Date: 11/20/08

Design:

        Research Question: How will a hypotonic solution (distilled water) affect osmosis and diffusion of a solution of starch and glucose in a dialysis (semi- permeable) membrane?

        Hypothesis: In a hypotonic solution, water concentration is greater outside the membrane than inside. Therefore, water will flow into the bag and the mass of the bag will increase. Glucose will diffuse out of the bag because it is a small molecule and the concentration of glucose is lower outside the bag than inside. Benedict’s solution will determine if this occurs. Starch is a large molecule and will remain in the bag regardless of the concentration gradient. This is due to the fact that the starch molecules are too large to pass through the pores of the dialysis membrane. Iodine will determine if this is true.

        Relevant Variables: Independent variable- diffusion of water, starch, and glucose. Dependent variables- mass and color changes. Other relevant variables- concentration, size of molecules, pore size of dialysis membrane, temperature, security of bag closure.

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        Control of Variables: using distilled water, using one solution source of starch and glucose, constant temperature, using only one type of dialysis membrane, securely tying the bag.

        Materials: ~20 cm dialysis tubing, ~40ml starch solution, ~ 75 ml distilled water, 200 ml beaker, scale, benedicts solution, iodine, hot plate, funnel, string.

        Procedure:

  1. Open the dialysis tubing by running cool tap water over one edge and rubbing layers together with fingers.
  2. Tie off one end securely with a piece of string. (draw a pic)

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