The Invisible Soup

Why it matters

Air feels like empty nothing, but it's a recipe — mostly nitrogen, a fifth oxygen, a pinch of argon. Mix a breath of it.

Predict first

Is air a compound or a mixture?

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

• A mixture — the gases are blended and the ratio can vary — correct
• A compound — the gases are chemically bonded
• 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 are only a ~1% trace.

Check yourself

Which gas makes up most of the air?

Nitrogen ~78%, oxygen ~21%, argon ~1%, CO₂ only a trace.

Why is air a mixture, not a compound?

Unbonded, separable, variable ratio — the marks of a mixture.

Oxygen is about what fraction of the air?

Oxygen is roughly one-fifth of the air.

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