Pure Substances & Mixtures

In chemistry, the word "pure" has a specific meaning that differs from everyday use. A pure substance consists of only one element or one compound. On the other hand, a mixture contains two or more different substances that are not chemically bonded together.

The three main categories of matter are elements, compounds, and mixtures. Elements and compounds are pure substances, while mixtures can be separated using physical processes without creating new substances.

One common separation technique is filtration, which separates an insoluble solid from a liquid (like sand from water). Filtration works because filter paper contains tiny pores that allow small molecules and dissolved ions to pass through while blocking larger particles.

Quick Tip: Think of filtration like a colander in your kitchen that lets water pass through but catches pasta!

Another important technique is crystallization, which produces solid crystals from a solution. This process involves warming the solution so some solvent evaporates, leaving crystals behind. For example, crystallization can be used to obtain copper sulfate crystals from copper sulfate solution. The process typically involves heating a solution in an evaporating basin, either directly or over a boiling water bath, then stopping the heat when crystals begin forming around the edges.