Kitchen Science

With thanks to June for supplying these excellent activities – if you have one to contribute – please let me know. June also runs HE-ED.

*IMPORTANT NOTE*

Kitchen science should be treated with the caution that all science is – and cleared away carefully to avoid children or animals having substances available in an uncontrolled environment. Please read packets of ingredients carefully and follow safety precautions. Better safe than sorry :~)

Making Flubber

Materials needed

Container 1

¾ cup warm water
1 cup white glue
food colouring (a couple of drops)

Container 2

2/3 cup warm water
½ teaspoons Borax

What to do
1) Mix the ingredients in each container thoroughly. Take note of how they both look, are they very different?

2) Pour the contents of container 2 into container 1. Lift and turn the mixture with a spoon until nearly all the liquid is gone. Gently squeeze any excess liquid from out of the Flubber.

3) What has happened? How does it feel? What happens if you stretch it? If you roll it in to a ball? If you place it over another object?

Polymers are made by a chemical reaction, they are long chains of repeating units. When the two solutions are combined, polyvinyl acetate chains (from the white glue) are linked together in a three-dimensional arrangement by Borate ions (from the Borax) and other chemical bonds. This produces the sticky polymer that we call Flubber.

Cabbage Acid-Alkaline Indicator

Materials needed

Pickled Red cabbage
Vinegar
Bicarbonate of Soda
A container

What to do

1) Remove the cabbage from the jar, as you only need the fluid that it was in.

2) Pour a little of the cabbage juice in to your container. Note the colour of the juice.

3) Put a small pinch of bicarb in to the juice. What happens?

4) Add a small amount of vinegar to the juice. What happens?

The colouring in the cabbage juice is an acid/alkaline indicator. When it is in an acid, such as vinegar, the juice turns red. When it is in an alkaline, such as bicarb, it turns blue-green. Do you have any other liquids that you could test?

Felt-Pen Chromatography

Materials needed

Felt-tip marker pens
Clear containers
Blotting paper
Water

What to do

1) Take a strip of blotting paper and choose a coloured marker pen (black works the best). About halfway up the strip of paper draw a horizontal line with the pen. Go over it a few times so that the colour is very concentrated.

2) Pour some water in to a clear container.

3) Dip the end of the blotting paper in the water, a couple of centimetres below the felt-pen line, and hold it as still as you can. What can you see happening?

4) When the water has travelled up to the tip of the blotting paper, place it on some paper towels to dry. What has happened to the felt-pen line? Is black ink really black, for instance?

Chromatography is the process of separating a mixture in to its components. The colour in the pens is made up of coloured substances, which have been dissolved in a liquid. When you colour with a felt-pen the liquid dries, and the colour is left behind. Therefore when the water creeps up the paper the dried colour dissolves again and is carried up the paper. Different colours are carried along faster and further by the water than others.
This works with mixtures other than felt-tip ink. Can you think of any times when this would be useful?