Welcome to a very eggy week on Science Sparks! Shrinking eggs is the first of 3 egg based experiments, so if you like this one, pop back later in the week to see what else we have been up to! This experiment looks at osmosis.
Osmosis is when water moves from a less concentrated solution to a more concentrated solution, through a semi permeable membrane.
Water flows from one side of a membrane to the other until the concentration of the liquid on both sides is equal.
What you need:
- Two eggs
- Two glasses
- A pin
The experiments has 3 stages.
- We need to remove the shell to expose the semi permeable membrane of the egg. This can be done by placing the eggs in a cup of vinegar so they are totally covered for about 24 hours. After this time wash the egg rubbing away the remaining bits of the shell.
- Make up a concentrated sugar solution by dissolving sugar in water, or you could use treacle. Place one egg in a glass of water, and the other in the sugar solution or treacle. Our sugar solution looks quite dark as I used brown sugar. Note how the egg in water sinks to the bottom of the glass while the one in the sugar solution floats. This is beacause the sugar solution is more dense than the water.
- Leave for another 24 hours. You can see the egg in the sugar solution looks much smaller than the one in the water.
Prick the egg from the water with a fine needle and watch a jet of water shoot out!
- Put the shrunken egg in water and watch it grow as it reabsorbs the water, this might take a few hours.
The science bit
The sugar solution is much more concentrated then the water, this is because it contains dissolved molecules of sugar. The dissolved molecules cannot pass through the semi permeable membrane of the egg, but the small water molecules can. The water moves from the less concentrated egg solution to the more concentrated sugar solution until the concentration is the same on both sides. Therefore water moves from the egg to the sugar solution, and the egg shrinks.
When the shrunken egg is placed back in water, the concentration of the liquid inside the egg is higher than the water, so water moves from the water to the egg, making the egg increase in size.
When we pricked the egg that had been in the water, water shot out of the egg. This is because the egg has absorbed water, and so the inside of the egg is under more pressure than usual.
The egg shell dissolves in the vinegar as the acetic acid in the vinegar reacts with the calcium carbonate of the the shell, Carbon dioxide is given off during this reaction so you should see bubbles of gas escaping.
Extra for older children
You could weigh the eggs after removing the shell, after they have been shrunken and again after they reabsorb water to see how much water is lost and gained at each stage.
You can add food colouring to the water and watch as the eggs absorb the coloured water.
Try soaking a boiled egg in vinegar, this should make the egg so rubbery it will bounce ( from a low height ).
Don’t forget to wash your hands after handling raw eggs!