A solution is a mixture with the same composition, color, density, and taste.  To describe a solution, there must be one or more substances dissolved in it.  A solute is a substance being dissolved, and a solvent is a substance doing the dissolving.  For example, if you add a spoonful of sugar to a glass of water, you have made a solution.  This is because the sugar dissolves in the water, so the sugar is the solute, and the water is the solvent.  Solutions can also be gaseous, like the air you breathe, or solid, like sterling silver.

When forming a solution, there are three ways to speed up the rate of the dissolving process.  First, stirring a solution brings more solvent in contact with the solute.  The solvent attracts the particles of the solute, causing the solute to dissolve faster.  Another way to speed up the dissolving process of a solid in a liquid is to increase the surface area.  Breaking up a solid and crushing it into powder allows more solvent to come into contact with the solute.  Finally, increasing the temperature of a solvent also speeds up the rate at which something dissolves.  Increasing the temperature speeds up particles, causing them to bump into each other, break apart, and come into contact with the solvent.

The maximum amount of solute that can be dissolved in a given amount of solvent under a given set of conditions is called solubility.  A substance’s solubility can change if the conditions change.  For example, you can dissolve more sugar in hot water than in cold water.   In addition, not every substance will dissolve in other substances, such as oil and water.  If a solute does not dissolve a solvent, it is called insoluble.

The amount of solute in any given solvent is called concentration.  It’s the percentage by volume of a solute in a solvent.  If something is concentrated, there is a large amount of solute in a solvent.  If something is dilute, there is a small amount of solute in the solvent.

A saturated solution contains all the solute it can hold at a given temperature.  If a solution is unsaturated, it means that it’s able to dissolve more solute at a given temperature.  Supersaturated means it contains more solute than a saturated one, and the solution is unstable.

Review:

1. In a solution, what is a solute? What is a solvent?
2. What does it mean if something is insoluble?
3. Compare saturated to unsaturated.