Composition of Air
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Composition of the atmosphere
Dry air is a mixture whose proportions have barely changed in 200 million years. About four-fifths of it by volume is nitrogen and about one-fifth is oxygen, with carbon dioxide, water vapour and the noble gases making up the small remainder. Knowing these approximate percentages is the baseline for every experiment that measures the oxygen fraction.
What you know already
From Group 7 (Halogens) you have just seen how gases such as chlorine behave and how their colours identify them. This note turns to the mixture above your head: what dry air is made of, the approximate percentages of its four most abundant gases, and how a simple reaction with a metal or non-metal measures the oxygen fraction.
Key points of understanding
- About 80 percent of dry air by volume is nitrogen, roughly four-fifths of the total.
- About 20 percent of dry air by volume is oxygen, roughly one-fifth of the total.
- Small proportions of carbon dioxide, water vapour and noble gases make up the remainder.
- The proportion of gases in the air has changed little in 200 million years.
- Carbon dioxide is present only in a very small amount yet it has a large warming role.
The atmosphere mainly consists of nitrogen and oxygen
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1.Composition of the atmosphere
Dry air is a mixture whose proportions have barely changed in 200 million years. About four-fifths of it by volume is nitrogen and about one-fifth is oxygen, with carbon dioxide, water vapour and the noble gases making up the small remainder. Knowing these approximate percentages is the baseline for every experiment that measures the oxygen fraction.
The atmosphere mainly consists of nitrogen and oxygen
Key points
- About 80 percent of dry air by volume is nitrogen, roughly four-fifths of the total.
- About 20 percent of dry air by volume is oxygen, roughly one-fifth of the total.
- Small proportions of carbon dioxide, water vapour and noble gases make up the remainder.
Guided content from the SME authoring corpus — note rn_6M5JB7CjvwdDykMS, pinned at 6fb25fc02d1a · promoted SyllabAI/syllabai-resources e967e75f1339
