When 5.20 g of salt is added to 5000 g of water, what is the concentration in parts per million (ppm)?

Hello!

Parts-per-million notation (ppm) is used for expressing small dimensionless quantities, usually ratios of mass to mass, volume to volume and so on.

In our problem, there are of salt and of water. Probably the ratio of mass to mass is required, although we can find densities of salt and water and calculate the volume to volume ratio, too.

The ratio is equal to  (dimensionless). In other words, there are  parts of salt for one part of water. Therefore there are

parts of salt for one million parts of water.

And this is the answer: the mass concentration is 1040 ppm. It may be expressed as 1040 ppm g/g also to avoid the confusion between masses and volumes.