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Practical Parenting: Kitchen chemistry - 18 August

Everything in the world is made up of chemicals, some natural, some artificial. Your kitchen is full of chemicals and you and your kids can become kitchen chemists.

Cooking is a form of chemistry. You take different ingredients and when they are mixed together they form something else.

Today we are going to look at three basic kitchen experiments that you can try with your kids.

1) The Acid Test

Some substances you find in the kitchen are acidic (e.g. lemon juice, vinegar) and some are alkali or bases (e.g. Bicarbonate soda). To discover whether a chemical is an acid or an alkali chemists will make a Chemical Indicator that reacts in different ways to an acid and to an alkali.

Red cabbage water is a basic chemical indicator that you can make in your own kitchen.

- Chop up some red cabbage and pour boiling water over it. Let it sit for 10 minutes; alternatively boil on stove for 10 minutes. (Supervise your children well with this part!)
- Sieve the cabbage and water until you are left with just the water, leave it to cool.
- Get three jars and put a little water in each, add a small amount of cabbage water to each jar.
- Add a different test liquid to each jar one at a time
- Try lemon juice, milk, vinegar, baking soda, fizzy coffee, tea
- Observe what happens to the colour of the cabbage water.
- If the substance is a acid the water will turn red or orange
- Bases or alkali turn the water purple or blue.
- Keep a "control" jar of cabbage water so you can compare the differences

2) The Magical Ice Cube

How can you get an ice cube to hang from a piece of cotton?

You need
Ice cube
Glass of cold water
15cm sewing thread

Put one ice cube into a glass of cold water, gently put the piece of thread  across the top of the floating cube.
Where the thread touches the ice, sprinkle 1/2 tsp of salt over.
Wait for 30 seconds and lift the thread, the cube should lift up too.
Why? Because salt lowers the freezing point of water it melts the ice a little, the thread will sink into a small pool of water in the ice cube and then it refreezes trapping the ice.

3) The Rubber Egg

How do you take the shell off a hard-boiled egg without cracking it?

You need
One hardboiled egg
Glass of vinegar

Hard boil the egg and put into the glass of vinegar, leave for three days
Then rinse the shell under water-the shell will wash off
Squeeze and poke it gently. How does it feel?
What Happens? The acid in the vinegar eats up the calcium carbonate of the egg shell leaving behind the skin or inner membrane of the egg.

Ideas from
The Big Book of Experiments and Activities, Koala Books
The Great Big Book of Things to Make and Do, Hermes House