Osmosis

Chemicals and Solutions

Saturated salt solution (about 1g NaCl/mL of water)

Materials

• About 6 inches of dialysis tubing
• 50 mL buret with tip removed
• Food coloring
• Dialysis tubing
• Tall beaker of water
• Celery, cucumber & white carnation

Procedure

1. Cut about 6 inches of dialysis tubing and soften it in water.
2. Tie one end of the dialysis tubing in a double knot to make a leak proof bag.
3. Secure the buret to a stand. Slide the open end of the dialysis bag around the 50 mL buret and pull the bag up so that the bag and tubing overlap for about one inch. Secure the bag around the buret using a rubber band.
4. Use food coloring to color about 100 mL of saturated salt solution and then add the salt solution to the dialysis bag by pouring it through the top of the buret. The bag should be filled with salt solution.
5. Immerse the bag in a beaker of saturated salt solution until classtime.
6. To present the demo, remove the beaker of saturated salt solution and immerse the bag in deionized water. Water will pass through the membrane into the bag causing the liquid level in the buret to rise.

Discussion

The dialysis tubing is a semipermeable membrane. Water molecules can pass through the membrane. The salt ions can not pass through the membrane. The net flow of solvent molecules through a semipermeable membrane from a pure solvent (in this cause deionized water) to a more concentrated solution is called osmosis.