What Is Parts Per Million?
Parts per million (ppm) is how many parts a certain molecule or compound makes up within the one million parts of the whole solution. It’s typically used to describe concentrations of chemicals dissolved in a solvent (typically water) or compounds in soil.
Calculating arts Per Million
So, we mentioned that 2 ppm = 0.0002%, but how would we calculate that? It’s actually pretty simple:
2/1000000 = 0.000002 * 100% = 0.0002%
However, converting ppm in percentage isn’t typically very helpful. Instead, we typically are given a ppm for a final solution and need to determine how much of the desired chemical to mix with water, or we are told how much of a certain compound is in soil and we need to determine the ppm.
Let’s say that we need to make 1 liter of a 50 ppm salt-water solution, how much water and how much salt should we use to make 1 liter? Let’s first think about 1 liter as being equal to 1000 mL. We simply need to set up a simple ratio, or setting two things equal to each other, to determine how much salt to use. As you can see:
So for every 1000 mL of solution, we need to use 0.05 g of salt in order to make a 50 ppm salt-water solution. In order to make this solution we would put 50 ppm of salt into a 1 liter container, and then fill the container to the 1 liter line.