Mixing Things Up with Solutes, Solvents, and Solutions

A solution is a homogeneous mixture, meaning that it’s the same throughout. If you dissolve sugar in water and mix it really well, for example, your mixture is basically the same no matter where you sample it.

A solution is composed of a solvent and one or more solutes. The solvent is the substance that’s present in the largest amount, and the solute is the substance that’s present in the lesser amount. These definitions work most of the time, but there are a few cases of extremely soluble salts, such as lithium chloride, in which more than 5 grams of salt can be dissolved in 5 milliliters of water. However, water is still considered the solvent, because it’s the species that hasn’t changed state.

In addition, there can be more than one solute in a solution. You can dissolve salt in water to make a brine solution, and then you can dissolve some sugar in the same solution. You then have two solutes, salt and sugar, but you still have only one solvent — water.

Most people think of liquids when they think about solutions, but you can also have solutions of gases or solids. Earth’s atmosphere, for example, is a solution. Because air is almost 79 percent nitrogen, it’s considered the solvent, and the oxygen, carbon dioxide, and other gases are considered the solutes. Alloys are solutions of one metal in another metal. Brass is a solution of zinc in copper.