Solutions — Definition & Examples

What Is a Solution?

$5 \times 5 = 25$, so $25$ is the solution, right? Yes, but not the kind we mean here! It can be an answer to a question, but when it comes to chemistry the term means something different. A solution is a uniform mixture of two or more substances. In a solution, a substance (solute) is dissolved in another substance (solvent). Solutes can be thought of as particles in a solution.

Solutions are homogenous mixtures which means that the combination of two or more substances is the same throughout. Solutions exist in one state (solid, liquid, or gas) and typically the solute takes on the state of the solvent.

Solution Example

If you take sugar (a solid solute) and add it to warm water (solvent) you have created a sugar liquid solution. The sugar dissolves in the so that is is indistinguishable from the water.

Solubility is important when considering making a solution. The solute must be soluble in the solvent. If we consider sodium chloride ($NaCl$) or salt, it is very soluble in water. $NaCl$ is not very soluble in acetone. To create a salt solution, using water is ideal.

Picking the Right Solvent

The most common solvents in chemistry are broken into two categories: aqueous and organic. Aqueous solutions use water as the solvent. Organic solvents are chemical liquids that can solvate different chemicals. A common organic solvent is acetone, (CH$_3$)$_2$CO. Acetone is found in nail polish and it will dissolve the polish to remove it from fingernails.

Ionic compounds, like salt, are made of positive and negative ions. Water ($H_2O$) is a polar solvent which has positive and negative charges in each molecule. Water is a good solvent for a lot of ionic compounds due to the interaction of the charges with the oppositely charged ions in ionic compounds. The $Na^+$ ion will interact with the partially negative oxygen of water. The $Cl^-$ will interact with the partially positive hydrogens of water.

A good rule of thumb to consider is "like dissolves like". Organic compounds will solvate or certain organic solvents. Non-polar compounds will solvate in non-polar solvents. When the correct solvent isn't clear, chemists will do solubility testing, a key approach chemists use when solving a problem. This involves a small amounts of solute and testing it with various solvents.

(Video) Solutions: Crash Course Chemistry #27

by CrashCourse

In this video, you will learn how to describe solutions in terms of molarity, molality, and mass percent. You will also learn about polar and nonpolar solvents, and about Henry's law.