Osmosis in the cosmosis
- Fill both of the dishes with water.
- Slice the potato lengthwise into several pieces that each have two flat sides (get Mom or Dad to help you with this step).
- Add about two tablespoons of salt to one of the dishes.
- Put half of the pieces in the dish that contains plain water.
- Put the other half of the pieces in the dish that contains the salt water.
- Let the potatoes soak for 20 minutes. If Dad assisted on step 2 then this would be a good time to go fetch the Band-Aids and help Dad patch up any resulting wounds.
Compare the potatoes. Notice any difference in the two?
Through osmosis, water naturally moves from areas of low salt concentrations to areas of high salt concentrations. Adding salt to the water creates a higher salt concentration in the water that is in the dish than in the water that is contained in the potato. Consequently, the water in a potato that is soaking in salt water will migrate out of the potato leaving a rather disgusting, mushy spud.
This is a good time to explain the term ‘samples’ as used in scientific experimentation. In this experiment we have created two controlled environments – one dish with potatoes and salt water and another dish with potatoes in regular water. Both of these controlled environments are termed ‘samples’.