Yummy Science - Magical Water. Experiments you can try in the kitchen - Custard Bouncing Balls, Self Slicing Banana, Growing Crystals, Spud Guns, Designer Onions, Honeycomb Toffee, Sticky Milk, Toast Busters, Toasty Science, Secret Messages

Science Links

More fun nutrition activities at
the Rowett Research Institute, eduweb
Check out National Science & Engineering Week at:
The BA (British Association for the Advancement of Science)

Further food science ideas for the primary aged audience are presented in the ‘Food for Thought resource, downloadable at The BA

For secondary pupils, there are lots of great kitchen chemistry ideas available in the Salters Chemistry Club handbooks or in various publications produced by the Royal Society of Chemistry

Exploring the science:

An object or liquid will float only in a liquid more dense than itself. Fresh water has a lower density than salt water - so that fresh water floats on top of sea water. The specific gravity of a liquid is used to compare its density relative to water. Pure water at 4^oC is said to have a specific gravity of 1.00, pure water at 20^oC has a specific gravity of 0.99, sea water at 20^oC a specific gravity of 1.02. A higher number means a denser liquid.

A hydrometer is an instrument used to measure specific gravity of liquids. You can make a very simple hydrometer from a length of drinking straw, mark the straw at regular intervals with a biro, add a piece of plasticine to one end, put the straw in a tall container of fresh water and adjust the size of the lump of plasticine so that it floats straight up and down. Now use your hydrometer to compare the densities of different liquids, the denser the liquid the higher the hydrometer floats.

Taking it further:

If you want to be really daring, gently introduce a fresh egg into the glass, it will hover magically between the two layers (but be careful not to mix the layers up as you introduce the egg). It floats because the density of salt water is sufficient to support a fresh egg, but the density of fresh water isn’t. Too daring? - then try a grape, this works just as well.
Why not have a go at setting up a ‘density column’ using a selection of household liquids such as syrup, oil, vinegar (acetic acid), water. Pour the different liquids into a tall container and allow them to settle out in layers. Drop small items into the column and see where they end up floating - try a grape, piece of pasta, lentil, walnut, button, wooden bead etc.

Liquids can float or sink just as solid objects can - it all depends on something called density. Fresh water has a density, sea water has a higher density - follow the instructions and see if you can use this information to make the contents of one glass of water float on top of another one!

You&0039;ll need:

Two glasses
Saturated salt solution (see recipe for ‘Growing Crystals’ for how to make a saturated solution). Colour the salt water with a few drops of food colouring.
Fresh water (no colouring added)
Plastic syringe

What to do:

To impress your friends….take two glasses of water, do not tell anyone that there is any difference between the two glasses of water apart from the colour. Say that you are going to add one glass of water to the other but you don’t want them to mix.
Take a syringe full of coloured sea water and introduce it very carefully into the glass of fresh water. The best way is to rest the tip of the syringe near the bottom of the glass and slowly empty the syringe. No syringe? Tilt the glass then pour the coloured water very slowly down the side of the glass.

N.B. If you add fresh water to salt water, the trick doesn’t work - this is because the fresh water rises through the salt water solution (because it is less dense) and mixes as it goes, simply diluting the salt water.

What happens:

You should now have a glass with two layers in it - a coloured layer on the bottom and a clear layer on top.