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How to Calculate PPM?

Published in Chemistry Calculations 3 mins read

PPM, or parts per million, is calculated by expressing the ratio of the mass of a solute to the mass of the solution, then multiplying by 1,000,000. Both the solute and solution masses must be in the same units (e.g., grams, kilograms, etc.).

Here's a breakdown of the calculation:

Formula:

PPM = (Mass of Solute / Mass of Solution) * 1,000,000

Steps Involved:

  1. Identify the Solute and the Solution: Determine what substance is being dissolved (solute) and what it's being dissolved in (solvent, which together forms the solution).

  2. Measure the Mass of the Solute: Find the mass of the solute in the desired units (e.g., grams, milligrams).

  3. Measure the Mass of the Solution: Find the mass of the entire solution, including the solute, in the same units as the solute. It is crucial that the units for the solute and the solution are the same.

  4. Apply the Formula: Divide the mass of the solute by the mass of the solution.

  5. Multiply by 1,000,000: Multiply the result from step 4 by 1,000,000 to obtain the PPM value.

Example:

Let's say you have a solution where 2 grams of salt (solute) are dissolved in 998 grams of water (solvent), resulting in 1000 grams of salt water solution.

PPM = (2 grams / 1000 grams) 1,000,000
PPM = 0.002 1,000,000
PPM = 2000

Therefore, the concentration of salt in the solution is 2000 PPM.

Important Considerations:

  • Units: Ensure the units for the solute and solution mass are consistent. If they aren't, convert them before performing the calculation.

  • Volume vs. Mass: While the most accurate method uses mass, PPM can also be approximated using volume if the density is near 1 (like dilute aqueous solutions). However, using mass is generally preferred for accuracy. In such case the formula become: PPM = (Volume of Solute / Volume of Solution) * 1,000,000 and units should be identical (e.g. mL, L, etc.)

  • Very Dilute Solutions: PPM is typically used for very dilute solutions, where the concentration of the solute is very small.

  • Conversion to other units: PPM can be converted to percentage by dividing PPM by 10,000. For example, 2000 PPM is equal to 0.2%.

Understanding how to calculate PPM is crucial in various fields such as chemistry, environmental science, and food science, where quantifying the concentration of trace substances is essential.

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