In this prac, you will be learning about diffusion, osmosis, hypertonic and hypotonic solutions.
This practical is basic and takes a few days, however it illustrates the principles of diffusion and osmosis perfectly I would suggest starting this prac on a Friday so the vinegar has the weekend to dissolve the egg shell.
Materials
Per student:
1 egg
1 beaker
Marker
Spoon
Vinegar
Corn syrup or honey
Distilled water
Food colouring
Method
Place the egg into the beaker and cover it with vinegar (depending on the beaker you may need 100 - 200 ml of vinegar). Almost immediately you should see bubbles forming.
Leave the egg for 2 - 3 days.
After 2 - 3 days the shell should be gone, wash away any left over shell and weigh your egg. BE CAREFUL, AS THE EGG IS VERY FRAGILE!
Once you have weighed your egg, place it in corn syrup or honey (a hyper tonic solution)
Leave the egg over night
Carefully remove the egg from the hyper tonic solution. Most of the water should have moved out of the egg, and left a sagging membrane with the yolk
Weigh the egg
Place the egg in a beaker of distilled water (hypo tonic solution) with food die in it.
Leave the egg over night
The egg should now be nice and round, filled with the food die.
Weigh the egg to see how much heavier it has become.
As you can see in the pictures, the initial weight of the egg was 84 grams.
When placed in a hypertonic solution it dropped down to 60 grams.
Then when placed into a hypotonic solution its weight increased to 109 grams
Science Behind the experiment
Dissolving egg shell
Vinger contains a chemical called Acetic acid. The egg shell contains calcium carbonate. When Calcium carbonate is exposed to Asetic acid, a chemical reaction occurs, converting Calcium carbonate to Carbon dioxide, water and calcium.
The equation is: CaCO3+ 2H+ -> Ca+2 + H2O +CO2
Observe the picture to the right. Those bubbles are caused by CO2 escaping.
The shrinking egg
As the egg now only has a membrane covering it, molecules can diffuse in and out.
When the egg is placed in honey or corn syrup, the egg will loose most of its water. This is because there is a higher concentration of water molecules inside the side than outside the egg.
When we place the deflated egg into a hypotonic solution (distilled water), water molecules flood into the egg. This is because they are going from an area of high concentration (outside) to an area of low concentration (inside). This is an example of Osmosis.
