Extraordinary Eggs
What you need:
· 1 fresh, uncooked egg (this shall be returned, unharmed if you are careful!)
· Top pan balance/digital scales OR a measuring spoon or scoop
· Cold tap water
· Salt (about 100g) — this shall be used up in the experiment
· A small plastic pot such as a clean empty yogurt pot
· A small spoon
· A spoon for stirring
· A measuring jug or other container
Be careful of:
- If your jug/container is glass, keep it away from the edge of your table
- Look after your egg, rest it on a plate whilst you stir, so it can’t roll away!
- Clean up carefully when you are finished, do not leave salty water on spoons or in cups etc.
Instructions:
1. Put your egg into your jug or container. You need to add enough cold water to just cover your egg. A fresh egg will sink!
2. Take your egg out of the water and put it somewhere safe. Record the volume (amount) of water in the jug. Top tip: try to use a nice round number, such as 400ml.
3. Put your empty clean yogurt pot or similar on your balance. Tare your balance (or adjust to zero). Add 100g of salt to your pot.
4. If you do not have a balance, fill your pot about two thirds full with salt. A 5ml medicine spoon (or a teaspoon if you don’t have one) hold about 6g of salt. You shall need to count spoons of salt if you can’t weigh it.
5. Carefully, add salt to the water. You can either use a measuring or medicine spoon and count how many spoons you add, or you can record the mass of salt you have added, using your balance.
6. After each addition of salt, stir the water until all of the salt has dissolved and you can’t see it any more. Be careful not to spill any water!
7. When the salt has dissolved, carefully put the egg back in the water and see what happens.
8. If the egg still sinks to the bottom of the jug, take it out again and add more salt.
9. Keep repeating steps 5 to 8 until the egg doesn’t sink. Make sure you record how much salt (mass in grams, or number of 5ml measuring spoons multiplied by 6g).
The science:
· Density is a measure of how much matter there is in a certain volume. A cube of metal weighs more than a cube of wood the same size. Water is more dense than vegetable oil. This is why oil floats on top of water.
· The density of the fresh egg is greater than the water. The egg is more dense, so it sinks.
· Salt dissolves in water to make a solution. The more salt you add, the more concentrated the solution becomes. The first solution you make after your first spoons of salt is a very dilute solution.
· When enough salt is added to make the density of the salt solution the same as the density of the egg, the egg (if you are careful!) can be suspended within the salt solution.
· Maths challenge: calculate the concentration of your salt solution, using the text box!
The challenge:
· If you keep adding salt and stirring carefully, then eventually, your egg shall float!
· Can you add salt carefully enough to be able to take a picture of your egg suspended in the water? Not sunk to the bottom, and not floating at the top.
· Can you calculate the concentration of salt in water you have used to suspend your egg in salt solution?
