Mixing the Atmosphere

Why it matters

Air looks like empty nothing, but it's a recipe: mostly nitrogen, a good helping of oxygen, and a pinch of argon. Mix a breath of it yourself.

Predict first

Is air a compound or a mixture?

Air is a mixture: about 78% nitrogen, 21% oxygen and ~1% argon (plus traces). The gases aren't bonded — they can be separated and the ratio can vary.

• A compound — the gases are chemically bonded
• A mixture — the gases are simply blended and their amounts can vary — correct
• A single pure gas

What you do

Build a breath of air: about 4 parts nitrogen to 1 part oxygen (~78% N₂, ~21% O₂). Argon and CO₂ make up only the last ~1% — a trace.

Check yourself

Which gas makes up most of the air?

Nitrogen is ~78% of air; oxygen ~21%; argon ~1%; CO₂ only a trace.

Why is air a mixture, not a compound?

The gases keep their identity and any ratio, and can be separated — so air is a mixture.

Roughly what fraction of air is oxygen?

Oxygen is about 21% — roughly one-fifth of the air.

• Nitrogen — correct
• Oxygen
• Carbon dioxide
• Its gases aren't chemically bonded and their amounts can vary — correct
• It has a fixed chemical formula
• It is invisible
• About one-fifth (21%) — correct
• About half
• Almost all of it