Chemistry / Unit 1: Matter and Measurement
1.3 Mixtures and Pure Substances
Notes
A pure substance has a fixed composition. A mixture is a physical blend of two or more substances.
- Pure substances are elements (one kind of atom, like Fe or $\text{O}_2$) or compounds (elements chemically bonded in a fixed ratio, like $\text{H}_2\text{O}$).
- A homogeneous mixture (solution) looks the same throughout: salt water, air, brass.
- A heterogeneous mixture has visibly different parts: salad, sand in water, granite.
- Mixtures can be separated by physical methods: filtration, distillation, evaporation, magnets, chromatography.
Practice
Salt water is best classified as a:
Salt dissolves evenly in water, so the mixture looks the same throughout.
Which is a compound?
$\text{CO}_2$ has two different elements chemically bonded. $\text{O}_2$ has only one element, and air is a mixture.
Which method would separate sand from water?
Sand particles are too big to pass through filter paper, while water goes through.
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