Glossary of Words

Summary of lessons so far

Molarity

Solutions are homogeneous mixtures. Many solutions contain one component, called the solvent, in which other components, called solutes, are dissolved. An aqueous solution is one for which the solvent is water. The concentration of a solution is a measure of the relative amount of solute in a given amount of solution.

Concentrations may be measured using various units, with one very useful unit being molarity, defined as the number of moles of solute per liter of solution. The solute concentration of a solution may be decreased by adding solvent, a process referred to as dilution. The dilution equation is a simple relation between concentrations and volumes of a solution before and after dilution.

Other Units for Solution Concentrations

In addition to molarity, a number of other solution concentration units are used in various applications. Percentage concentrations based on the solution components’ masses, volumes, or both are useful for expressing relatively high concentrations, whereas lower concentrations are conveniently expressed using ppm or ppb units. These units are popular in environmental, medical, and other fields where mole-based units such as molarity are not as commonly used.

Key Equations

• \(M = \frac{\text{mol solute}}{\text{L solution}}\)
• \(C_1V_1 = C_2V_2\)
• \(\text{Percent by mass} = \frac{\text{mass of solute}}{\text{mass of solution}} × 100\)
• \(\text{ppm} = \frac{\text{mass solute}}{\text{mass solution}} × 10^6\text{ ppm}\)
• \(\text{ppb} = \frac{\text{mass solute}}{\text{mass solution}} × 10^9\text{ ppb}\)

Glossary of words

Aqueous solution

solution for which water is the solvent

Concentrated

qualitative term for a solution containing solute at a relatively high concentration

Concentration

quantitative measure of the relative amounts of solute and solvent present in a solution

Dilute

qualitative term for a solution containing solute at a relatively low concentration

Dilution

process of adding solvent to a solution in order to lower the concentration of solutes

Dissolved

describes the process by which solute components are dispersed in a solvent

Mass percentage

ratio of solute-to-solution mass expressed as a percentage

Mass-volume percent

ratio of solute mass to solution volume, expressed as a percentage

Molarity (M)

unit of concentration, defined as the number of moles of solute dissolved in 1 liter of solution

Parts per billion (ppb)

ratio of solute-to-solution mass multiplied by 109

Parts per million (ppm)

ratio of solute-to-solution mass multiplied by 106

Solute

solution component present in a concentration less than that of the solvent

Solvent

solution component present in a concentration that is higher relative to other components

Volume percentage

ratio of solute-to-solution volume expressed as a percentage