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/m^{3} = 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/m^{3} = 1mg/L = 1μg/mL
1. A solution has a concentration of 1.25g/L.
What is its concentration in ppm?

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

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?

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

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?

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

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?

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

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).

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

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

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 KNO_{3(aq)} ?

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

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

Substitute in the values:
mass KNO_{3} = 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?

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

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

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

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

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