Pure Gold or Dirty Mud?
Sort substances into elements, compounds, and mixtures.
What this lesson covers
Why it matters
A gold bar is one element through and through. Pure water is one compound. Mud is a jumble of soil, water and air. Three kinds of matter, three different recipes.
Predict first
What is the key difference between a compound and a mixture?
An element is one kind of atom. A compound is elements chemically bonded in a fixed ratio. A mixture is substances blended in any ratio, each keeping its own properties.
- A compound's elements are chemically bonded in a fixed ratio; a mixture is just blended — correct
- A compound is always heavier
- There is no real difference
What you do
Sort each one: is it an element, a compound, or a mixture?
Check yourself
Which of these is a compound?
CO₂ is carbon bonded to oxygen in a fixed ratio; brass is a mixture and oxygen an element.
A mixture differs from a compound because…
A mixture is just blended — variable ratio, properties retained, easy to separate.
Sea water can be separated into salt and pure water just by evaporation. What does this prove?
Only mixtures can be separated by physical methods like evaporation — the salt and water each kept their own identity all along.
- Carbon dioxide (CO₂) — correct
- Brass
- Oxygen
- its parts keep their own properties and can be in any ratio — correct
- it always has a fixed chemical formula
- it is always a solid
- Sea water is a mixture — its parts separate by physical means — correct
- Sea water is a compound of salt and water
- Sea water is an element