Question

A 2400-gram sample of an aqueous solution contains 0.012 gram of `NH_3`. What is the concentration of `NH_3` in the solution, expressed as parts per million?

Answer 1

`"Parts per million "= " Milligram per litre of solution"`. The concentration of the solution is `5` `"ppm"`.

Explanation:

At `"ppm"` concentrations, we don't have to bother with consideration of the density of the solvent versus the density of the solution; in any case we don't have these details.

There are `12xx10^-3` `g` ammonia in a `2400` `g` mass of solution. We assume (reasonably) that the volume of the solution is `2.400*L`.

So `"concentration"` `=` `(12xx10^-3gxx10^3*mg*g^-1)/(2.400*L)` `=` `(12*mg)/(2.400*L)` `=` `5*mg*L^-1` `=` `5` `"ppm"`