Diffusion and Osmosis

IMPORTANT: Wear gloves, goggles, and appropriate personal protective equipment – chemicals can be hazardous at high concentrations.

For the diffusion indicator solution, weigh out 1 g of phenolphthalein and add it to a beaker containing 100 mL of 95% ethanol.

To make the basic solution for the agar, measure 80 mL of water into a beaker, and then add 0.4 g of NaOH.

Stir until the solute is dissolved then bring the total volume of the solution to 100 milliliters to make a 0.1 molar solution.

To make the diffusing acid, measure out 25 mL of HCl and add it to 475 mL of water. NOTE: Plan to make around 500 mL of this HCl solution per work group.

IMPORTANT: Agar needs time to cool, so prepare several hours in advance of the class.

To prepare the agar, first weigh out 20 g of dehydrated agar powder and then add this to 1 L of water.

Heat the solution to near boiling or until it becomes fully clear.

Then, cool the agar to 55 °C and add 10 mL of the phenolphthalein ethanol solution.

Slowly add the 0.1 molar sodium hydroxide solution to the agar until it becomes vibrant pink.

Take a clean tray with deep sides and pour the agar to a depth of 3 cm.

Place the tray into the refrigerator for a few hours.

To prepare the 1% starch solution, weigh out 10 g of soluble starch and add it to 500 mL of distilled water set on a magnetic stir plate.

When the solute has dissolved, bring the final volume of the solution up to 1 L with more water.

To prepare 1M NaCl, dissolve 58.4 g of NaCl in 500 mL of distilled water, in a 1 L container. Then, bring the volume up to 1 L with distilled water.

To prepare 1M dextrose, add 180.2 g of dextrose powder to 500 mL of distilled water in a 1 L beaker. Once dissolved, bring the volume up to 1 L with distilled water.

Cut the dialysis tubing into 20 cm pieces.

Place the pieces to soak in distilled water; make sure they are kept moist at all times. NOTE: Excess tubing can be stored at 4 °C in 20% ethanol to prevent bacterial growth.