Mixtures & Solutions

When two or more substances are combined without forming a new substance, the result is a mixture. Each part of a mixture keeps its own properties, which means a mixture can usually be separated back into its parts using a physical method.

Two Kinds of Mixtures

• Heterogeneous mixture — the parts are not evenly mixed and you can see them, like a salad, sand and water, or trail mix.
• Homogeneous mixture (also called a solution) — the parts are evenly mixed and look like one substance, like salt water, sugar water, or air.

Solutions: Solute + Solvent

A solution is a special mixture in which one substance dissolves into another. The thing that gets dissolved is called the solute. The thing that does the dissolving is called the solvent. Water is the most common solvent on Earth — it dissolves so many things that scientists call it the universal solvent.

• Salt water — salt is the solute, water is the solvent.
• Sugar in tea — sugar is the solute, the tea (water) is the solvent.
• Soda — carbon dioxide gas is dissolved in flavored water.

Separating a Mixture

Because the parts of a mixture keep their own properties, you can pull them back apart. The right method depends on the kind of mixture.

• Filtering — pour the mixture through a filter to catch the solid (sand from water).
• Evaporation — let the liquid evaporate so the solid is left behind (salt from salt water).
• Magnet — pull out anything that is magnetic (iron filings from sand).
• Sieve — shake the mixture through a screen to separate big pieces from small ones (rocks from sand).