الأسبوع 1 · الفصل 1 «شروط الاحتراق»: 1-1 كيف تحترق الأشياء والهواء، 1-2 دور الأكسجين · 3 دروس
2
What air is made of
Science P6: Term 1, Chapter 1, pp. 6–11
GoalName the gases in air and say roughly how much of each there is.
New words
air · the mixture of gases around usnitrogen · the gas that makes up about four fifths of airoxygen · the gas in air that helps things burn and that we breathecarbon dioxide · a gas present in air in a very small amount
Explanation
Air is a mixture of gases, not a single gas. About four fifths of it is nitrogen, and about one fifth is oxygen. There are also very small amounts of carbon dioxide and other gases. You cannot see these gases, but they are all around you. Think of a fruit salad: the pieces are mixed together but are still different fruits. In air, nitrogen is the biggest part. Oxygen is only about one fifth, but it is the part that helps fuels burn and that animals need to breathe. Nitrogen and carbon dioxide do not help things burn. Carbon dioxide is even used in some fire extinguishers to help put fires out.
Worked examples
A classroom has air. Hana wants to find the part of the air that helps fire. She finds that it is oxygen, about 1 part in every 5 parts of air.
Gas
About how many in 100
nitrogen
78
oxygen
21
carbon dioxide and others
1
If you could count 100 small pieces of air, about 78 would be nitrogen, about 21 oxygen and about 1 something else. The pieces of nitrogen are the most, so nitrogen is the biggest part.
Helps burning
Does not help burning
oxygen
nitrogen
carbon dioxide
Youssef sorts gas cards into two piles: gases that help burning and gases that do not.
Class activity
Air mix model. With a grown-up, take 10 coloured beads or buttons. Use 8 of one colour for nitrogen and 2 of another colour for oxygen. This is a small model of air: about four fifths and one fifth. Why is the model not exactly right? (Hint: it leaves out carbon dioxide.)
Practice
1
Which gas makes up the biggest part of air?
Nitrogen.
2
About how much of air is oxygen?
About one fifth.
3
Is air one gas or a mixture?
A mixture of gases: mainly nitrogen and oxygen.
4
Which of these helps things burn: nitrogen, oxygen or carbon dioxide?
