Demonstration of How Osmosis Works

Osmosis is a process in which different concentrations of solutions move through semi-permeable membranes. The transfer occurs from the highest concentration to the lowest. Osmotic pressure is a term used to explain the force with which the molecules transfer from the solution of higher concentration into the solution of lower concentration. Osmosis occurs throughout nature and one example is plants absorbing nutrients through their roots.

This experiment will demonstrate how the process of osmosis works by using distilled water and a water/sugar solution. The experiment will require about 10 minutes of set-up time and 3 to 4 hours to observe the results.

Materials Required

• A beaker or a transparent bowl (glass or plastic)
• Concentrated sugar solution (Fill a bowl with 2 cups of warm water and add as much sugar as will easily dissolve)
• Distilled water
• A thistle funnel (a glass funnel which has a calibrated, long tube). Any transparent funnel will work
• Some form of semi-permeable membrane (parchment paper works well)
• Twine or a twist tie (from a bread bag) to secure the membrane to the funnel
• A small clamp to hold the funnel in place
• Food coloring (optional). The food coloring will make it easier to see when the transfer begins to take place
• Journal to record your findings

Procedure

1. Fit a piece of the semi-permeable membrane around the bottom of the funnel and use the twine or twist tie to secure it firmly.
2. Fill the beaker ¾ of the way with the distilled water. If you chose to use food coloring, add a few drops to the beaker and stir.
3. Turn the funnel so that the covered portion is at the bottom and then fill the funnel about half way with the sugar solution
4. Immerse the covered end of the funnel in the beaker of sugar solution making sure to leave a gap between the covered portion of the funnel and the bottom of the beaker.
5. Clamp the thistle funnel in an upright position so that it isn’t resting against the bottom of the beaker.
6. Use a marker to mark the level of the liquid in the thistle funnel’s tube and allow your experiment to sit for a few hours.

When filling the beaker and funnel, the beaker can be filled as far as ¾ full, but enough room must be left in the funnel for the liquid level to rise during the course of the experiments.

Check on the experiment every hour or so and record any difference in the liquid level of the funnel.

You should notice that the liquid level in the funnel is slowly rising and that the membrane covering the bottom looks as if it is being sucked into the tube of the funnel. The rising level of liquid in the funnel is due to the movement of the distilled water (lower concentration) into the tube of the beaker filled with sugar water (higher concentration).

A simpler form of this experiment is to slice a potato about into ½ inch thick slices and add a slice to a cup of very strong salt water and another to a cup of plain, distilled water. The potato slice in the salt water will become limp and wilted after a few hours while the slice in the plain water will remain crisp. This is because the liquid from the potato slice in salt water gradually transfers to the area of higher concentration while the potato slice in plain water gradually absorbs water from the cup into itself.