Parts per Million

When a solution is too diluted, it is preferable to refer to its concentration in terms of parts per million (ppm).

You will notice that the formula to determine parts per million is very similar to that for determining percent by mass.

One very important thing you must consider is that, since these solutions are very diluted, the mass of the solution is approximately equal to the mass of the solvent.   

 

In the case of water solutions, we will assume the density of such solutions to be equal to that of water (1.00 g/ml).

 

The formula to calculate parts per million is:

Notice that, if percent by mass was equal to the solute/solution ratio multiplied by 100, parts per million is the same ratio multiplied by 1 million.

 

Please review the following examples.