How it works
This classifying matter quiz names 32 everyday substances, from table salt and brass to granite and air. Sort 18 as element, compound or mixture, then 14 mixtures as homogeneous or heterogeneous. Each answer comes with one line that says why.
Read the full guide
Element, compound or mixture
An element is one kind of atom. A compound is two or more elements bonded in a fixed ratio, so it has one formula. A mixture is substances mixed without bonding, in amounts that can vary.
Homogeneous or heterogeneous
A homogeneous mixture is uniform throughout, like salt dissolved in water. In a heterogeneous mixture the parts can be told apart, like sand in water.
- Alloys such as brass and steel are mixtures: the recipe can change, and a compound's cannot.
- Two atoms of the same element, as in oxygen gas, still make an element.
Questions and answers
How do you classify matter?
First ask whether it is a pure substance or a mixture. A pure substance is an element or a compound. A mixture is homogeneous if it is uniform throughout and heterogeneous if its parts can be told apart.
Is air an element, a compound or a mixture?
A mixture. Dry air is about 78% nitrogen and 21% oxygen, with argon, carbon dioxide and other gases. The gases are evenly mixed, so air is a homogeneous mixture.
Is water a compound or a mixture?
Pure water is a compound, H2O: two hydrogen atoms bonded to one oxygen atom, always in that ratio. Sea water is a mixture, because salts are dissolved in the water.
Is salt water homogeneous or heterogeneous?
Homogeneous, once the salt has fully dissolved. The salt spreads evenly through the water, so every sample is the same. A mixture like this is called a solution.