Pure Gold or Mixed Salad?
Spot the difference between pure substances and mixtures.
Setting up the bench…
What this lesson covers
Why it matters
Pure gold melts at exactly 1064°C, every time. A bowl of fruit salad has no single melting point at all — because it's many things at once.
Predict first
Why does a pure substance have one sharp melting point, but a mixture doesn't?
A pure substance is one kind of particle, so it melts at one fixed temperature. A mixture has different particles that melt over a range.
- Pure substances are made of one kind of particle with fixed properties — correct
- Mixtures are always too cold to melt
- Pure substances are heavier
What you do
Sort each: a single pure substance, or a mixture of several?
Check yourself
Which observation proves a sample is a pure substance?
A sharp fixed melting/boiling point is the hallmark of a pure substance.
Why is sea water a mixture?
Sea water is water plus dissolved salts (variable amounts) — a mixture you can separate by evaporation.
- It melts at one sharp, fixed temperature — correct
- It looks clear
- It can be filtered
- It is water with dissolved salts, in no fixed ratio — correct
- It is a compound of salt and water
- It is a single element