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Parts Per Million (ppm) Concentration

Key Concepts

  • For very dilute solutions, weight/weight (w/w) and weight/volume (w/v) concentrations are sometimes expressed in parts per million.

  • parts per million is abbreviated as ppm

  • 1 ppm is one part by weight, or volume, of solute in 1 million parts by weight, or volume, of solution.

  • In weight/volume (w/v) terms, 1ppm = 1g/m3 = 1mg/L = 1μg/mL

  • In weight/weight (w/w) terms, 1ppm = 1mg/kg = 1μg/g

Converting weight/volume (w/v) concentrations to ppm

ppm = 1g/m3 = 1mg/L = 1μg/mL

1. A solution has a concentration of 1.25g/L.
What is its concentration in ppm?

  1. Convert the mass in grams to a mass in milligrams:
    1.25g = 1.25 x 1000mg = 1250mg

  2. Re-write the concentration in mg/L = 1250mg/L = 1250ppm
2. A solution has a concentration of 0.5mg/mL.
What is its concentration in ppm?

  1. Convert the volume to litres:
    volume = 1mL = 1mL ÷ 1000mL/L = 0.001L

  2. Re-write the concentration in mg/L = 0.5mg/0.001L = 500mg/L = 500ppm

Converting weight/weight (w/w) concentrations to ppm

1ppm = 1mg/kg = 1μg/g

1. A solution has a concentration of 0.033g/kg.
What is its concentration in ppm?

  1. Convert mass in grams to mass in milligrams:
    0.033g = 0.033g x 1000mg/g = 33mg

  2. Re-write the concentration in mg/kg = 33mg/kg = 33ppm

2. A solution has a concentration of 2250μg/kg.
What is its concentration in ppm?

  1. Convert mass in μg to mass in mg:
    2250μg = 2250μg ÷ 1000μg/mg = 2.25mg

  2. Re-write the concentration in mg/kg = 2.25mg/kg = 2.25ppm

Parts Per Million (ppm) Concentration Calculations

1. 150mL of an aqueous sodium chloride solution contains 0.0045g NaCl.
Calculate the concentration of NaCl in parts per million (ppm).

  1. ppm = mass solute (mg) ÷ volume solution (L)

  2. mass NaCl = 0.0045g = 0.0045 x 1000mg = 4.5mg
    volume solution = 150mL = 150 ÷ 1000 = 0.150L

  3. concentration of NaCl = 4.5mg ÷ 0.150L = 30mg/L = 30ppm
2. What mass in milligrams of potassium nitrate is present in 0.25kg of a 500ppm KNO3(aq)?

  1. ppm = mass solute (mg) ÷ mass solution (kg)

  2. Re-arrange this equation to find the mass of solute:
    mass solute (mg) = ppm x mass solution (kg)

  3. Substitute in the values:
    mass KNO3 = 500ppm x 0.25kg = 125mg
3. A student is provided with 500mL of 600ppm solution of sucrose.
What volume of this solution in millilitres contains 0.15g of sucrose?

  1. ppm = mass solute (mg) ÷ volume solution (L)

  2. Re-arrange this equation to find volume of solution:
    volume solution (L) = mass solute (mg) ÷ ppm

  3. Substitute in the values:
    volume solution (L) = (0.15g x 1000mg/g) ÷ 600 = 0.25L

  4. Convert litres to millilitres: volume solution = 0.25L x 1000mL/L = 250mL


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