Pour a teaspoonful of salt into a glass of water.
Now stir it and watch the salt slowly disappear from sight.
It is dissolving in the water.
How do you know the salt is still there?
Try tasting a drop of the water.
Gases also dissolve in liquids.
There is a great deal of dissolved oxygen in both salt water and fresh water.
Fish take in water and extract the oxygen from it. This is the way they breathe.
Every time you have a carbonated drink, you are drinking gas that has been dissolved in liquid.
This gas is carbon dioxide.
Pressure is used to make carbon dioxide dissolve.
The carbonated drink is still under pressure when it is canned in a factory.
When you open a can containing a carbonated drink, you release the pressure and thousands of bubbles of carbon dioxide stream to the surface.
As you drink, you can feel some of the bubbles popping on your tongue.
If you shake the can before opening it, you will increase the carbonation in the drink.
Shaking the drink makes more tiny bubbles of gas form.
When the can is opened, the gas in these bubbles expands instantly, making the drink froth and foam.
If you leave the can open, the carbonation will eventually disappear.
Because it is no longer under pressure, the carbon dioxide will escape into the atmosphere.
Try producing bubbles of gas in a liquid for yourself.
You will need:
- a teaspoon
- baking powder
- a glass
Put half a teaspoonful of baking powder into a glass and add water.
Stir the mixture.
Describe what happens as the baking powder dissolves.
To show that there is air dissolved in water, fill a glass with tap water and leave it for several hours.
What has happened inside the glass?