Parts per million (ppm)

Definition

Parts per million (ppm) is a unit of concentration that denotes the number of parts of a substance in one million parts of the total solution. It is commonly used to measure very dilute concentrations.

5 Must Know Facts For Your Next Test

1. 1 ppm is equivalent to 1 milligram of solute per liter of solution (mg/L).
2. $\text{ppm}$ can be converted to $\text{percentage}$ by multiplying by $10^{-4}$.
3. ppm is especially useful for measuring contaminants in water and air.
4. To calculate ppm, use the formula: $\text{ppm} = \left(\frac{\text{mass of solute}}{\text{mass of solution}} \right) \times 10^6$.
5. In gas mixtures, ppm can be calculated using volume ratios.

Review Questions

• How many milligrams per liter does 1 ppm represent?
• What formula would you use to calculate ppm from mass measurements?
• How do you convert a concentration from ppm to percent?

Related terms

Molarity:

A unit of concentration measured as moles of solute per liter of solution (mol/L).

Molality:

A measure of solute concentration defined as moles of solute per kilogram of solvent (mol/kg).

Percent Composition:

The percentage by mass of each element in a compound or component in a mixture.