Instructables
Picture of How to teach osmosis
osmosis.jpg
I originally used this instructable as a demonstration to explain osmosis to my classes.
Over the years many of my pupils told me they'd tried it for themselves at home (got their interests, half my job was done).  I've started using this method as a practical with some of my classes with great results and plenty of opportunities for pupils to visualise  cells and osmosis also  for extension work to challenge the more able (you know the one that has finished, while you're still explaining what to do to others).
Over all it does take 5 days but you can take about 2 days off by putting the eggs in vinegar yourself but it does loose some of its WOW.
I took these photos before I decided to make this instructable so sorry if photo doesn't quite fit the step.

Step 1: Equipment

Picture of Equipment
2 x eggs
about 500ml of vinegar (I normally use the distilled white vinegar, but this bottle was only 14p)
2 x 250ml Beakers
bag of sugar
2 x 500ml beakers
Post it notes or Sticky labels

1 x balance (the more accurate the better)

Step 2: Dissolve the egg shells

Picture of Dissolve the egg shells
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Place each of the eggs into a 250ml beaker and cover with vinegar. Place them in a spot where they wont be tampered with, (then put them somewhere even safer with a note on them, saying "do not touch"). Leave for 2-3 days (over weekend is best, you can set them up on a Friday lesson and revisit Monday/Tuesdayish.

Step 3: The fun part

Picture of The fun part
The eggs now have no shells but are intact. Retrieve them using a spoon, or gently emptying the beakers into a sink.
This is normally the only problem part as some pupils are put off by the smell of vinegar.
I am always paranoid of the bursting them, but this hasn't happened yet, and the ones that get dropped are easily cleaned up with some paper towels.

Step 4: Measuring the mass

Picture of Measuring the mass
Place each egg on a balance and measure its mass as accurately as the equipment allows.
write each mass and conditions that each egg will be kept in on a separate label.
 
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lcat2 years ago
Excellent!
lmperkins2 years ago
Nice job. I teach organic chemistry, but I'll forward this to my general chemistry colleagues.
Sovereignty2 years ago
Are you entering this project in the teacher contest?
148734 (author)  Sovereignty2 years ago
hello. yes, I am hoping to enter the contest . Would appreciate the votes ;)
Sovereignty2 years ago
Thanks. Home school teachers appreciate this kind of project.
TheGreatS2 years ago
Wonderful Instructable, bravo. When I did this, watching the eggs grow and shrink was very exiting. Try putting the eggs in Karo syrup or corn syrup. The effects are very dramatic ;-). Hooray for science!
kelseymh2 years ago
Yay, science! I'm a working physicist, and p-chem like this has always been my downfall. Somehow, the fact that osmotic pressure can work even in the absence of a physical pressure difference still seems like magic :-)