Pure or Impure? Sort It!
Sort substances into pure substances and mixtures.
Setting up the bench…
What this lesson covers
Why it matters
Distilled water is nothing but H₂O. Sea water is water plus a dozen dissolved salts. One is pure; one is a mixture in disguise.
Predict first
What makes a substance 'pure'?
A pure substance (element or compound) has a fixed composition and a sharp melting point. A mixture is two or more substances jumbled in any ratio.
- It is a single substance with a fixed composition — correct
- It simply looks clean and clear
- It is always a liquid
What you do
Sort each: a pure substance, or a mixture?
Check yourself
Which is a pure substance?
Distilled water is only H₂O; air and sea water are mixtures.
A pure substance has…
A single sharp melting point is the mark of a pure substance.
- Distilled water — correct
- Air
- Sea water
- a sharp, fixed melting point — correct
- a wide range of melting points
- visible separate parts