Acids and Alkalis

The pH scale measures the acidity or alkalinity of something.

An indicator is a chemical substance which turns different colours in acids and alkalis. Many indicators come from natural dyes in plants, for example red cabbage.


Gases in air

there are more than 10 gases in air, but the nost important ones are:

  1. Nitrogen
  2. oxygen
  3. argon
  4. carbon dioxide

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an oxygen molecule is made of two oxygen atoms.
When substances burn they are joining up with oxygen.
If a glowing splint is put in oxygen, the splint burns with a bright flame
Oxygen is an element.

Carbon dioxide

Carbon dioxide molecule is made up by 1 carbon atom and 2 oxYgen atoms.
It does not burn, it also puts out most things that are burning.
When you shake it with lime water (clear liquid) it turns milky white. This is the only gas that changes lime water.
It is made up by two elements,it is a compound.


It is a nobel gas. It is not usual for it to join with other chemicals.
It also puts out things which are burning.
It is made up by a single atom of argon.
It is an element.


Is it is less dense than air, helium rises above, it is used to fill ballons, airships and other light things.

It glows red when electricity passes through it.

Is used to freeze food. Nitrogen is very cold, it freezes things staight away.
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bulbs are filled with argon. With this, the wire inside can get very hot without burning.

Is used to help people breathe,
to produce very hot flames.

Carbon dioxide
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Used in making dry ice,
as fizzy gas for fizzy drinks,
for fire extinguishers.

In process...
when a test tube is put over a burning candle inside a water vessel, the candle goes out and the water level rises inside the test tube.when magnesium is being burnned it shines. After it is burnned a white ash is formed.When carbon is burned in air, the gas produced turns lime water milky,
this means it turns into carbon dioxide.
Breathing and producing energy go "hand in hand". the body needs one to do the other.
As food and oxygen join up, energy is produced.