Parts per million (ppm)
Expresses very low concentrations as parts of solute per million parts of solution.
What is Parts per million (ppm)?
A unit of concentration representing the number of parts of a solute for every one million parts of a solution or mixture.
Key formula / rule: ppm by mass
Key points
- Understand the concept and utility of ppm.
- Learn to calculate ppm using different methods.
- Relate ppm to other concentration units for dilute solutions.
- Appreciate its application in real-world scenarios.
Common exam trap
Confusing mass and volume units.
Definitions
- Term
Parts per million (ppm)
- Meaning
A unit of concentration representing the number of parts of a solute for every one million parts of a solution or mixture.
- Term
Dilute solution
- Meaning
A solution in which a small amount of solute is dissolved in a large amount of solvent.
Learning objectives
Understand the concept and utility of ppm.
Learn to calculate ppm using different methods.
Relate ppm to other concentration units for dilute solutions.
Appreciate its application in real-world scenarios.
Formulae
- Name
ppm by mass
- Note
Used when both solute and solution masses are known.
- Expression
$$ \text{ppm} = \frac{\text{mass of solute}}{\text{mass of solution}} \× 106 $$
- Name
ppm by volume
- Note
Used when both solute and solution volumes are known.
- Expression
$$ \text{ppm} = \frac{\text{volume of solute}}{\text{volume of solution}} \× 106 $$
- Name
ppm for dilute aqueous solutions
- Note
Assumes density of solution is approximately 1 g/mL.
- Expression
$$ \text{ppm} \≈ \frac{\text{mass of solute (mg)}}{\text{volume of solution (L)}} $$
Prerequisites
Understanding of basic concentration units (mass percentage, volume percentage).
Familiarity with units of mass and volume.
Concept of dilute solutions.
Common mistakes
Confusing mass and volume units.
Assuming density is always 1 g/mL for all solutions.
Incorrectly converting between ppm and other concentration units like molarity.
Forgetting to multiply by 10⁶ in the formula.
Keywords
ppm
parts per million
concentration
dilute solutions
trace amounts
environmental chemistry
analytical chemistry
mg/L
Practice preview
What is the meaning of 'parts per million' (ppm) in chemistry?…
easy
If 0.02 grams of a solute is dissolved in 100 grams of a solution, what is the concentration of the solute in ppm?…
easy
A solution is prepared by dissolving 50 mg of a salt in 250 mL of water. Assuming the density of the solution is approximately 1 g/mL, calculate the concentration of the salt in ppm.…
medium