Section 1 - What Is a Solution? Mixtures You have learned about the difference between pure substances and mixtures. Mixtures can either be heterogeneous or homogeneous. The particles of a heterogeneous mixture are large enough to see under a microscope. In a homogeneous mixture, however, the particles are molecule-sized, so the mixture appears uniform, even under a microscope. A homogenous mixture is also known as a solution. Solutions Are Stable Homogeneous Mixtures Two substances when mixed together to create a solution will not separate over time. If separation occurs between two substances it is not a true solution.

Solution Is a Broad Term Any mixture that is homogeneous on a microscopic level is a solution. According to that definition, air is a gaseous solution. However, when most people use the word solution, they are usually referring to a homogeneous liquid mixture. A homogeneous liquid mixture has one main component—a liquid—as well as one or more additional ingredients that are usually present in smaller amounts. The primary ingredient in a solution is called solvent, the and the other ingredients are the solutes and are said to be dissolved in the solvent. Water is the most common solvent. Although it is a very common substance, water is a unique solvent because so many substances can dissolve in it. Solutions in which water is the solvent are called aqueous solutions.

Separating Mixtures There are many ways to separate mixtures into their components. The best method to use in a particular case depends on the kind of mixture and on the properties of the ingredients. Method 1 –Decanting Decanting separates a liquid from solids that have settled. To decant a mixture, carefully pour off the liquid to leave the solids behind.

Method 2 – Centrifuge A centrifuge is used to separate substances of different densities. The centrifuge spins rapidly, and the denser substances collect at the bottom of the tube. Method 3 – Filtration Ground coffee is separated from liquid coffee by filtration. The filtrate—the liquid and whatever passes through the filter—collects in the coffeepot. The solid grounds stay on the filter.

Method 4 – Evaporation In saltwater ponds such as this one, sea water evaporates, and salts, mainly sodium chloride, are left behind. Method 5 – Distillation If the boiling points of the components are different, distillation can separate them based on their boiling points. As one component reaches its boiling point, it evaporates from the mixture and is allowed to cool and condense.