Let's state the problem: we know the concentration of CaCl2 (calcium chloride) in the solution in ppm (parts per million). We need to find chlorides WPS (water phase salinity) in ppm.
The conversion looks quite straightforward. However, I am not a chemist, so that I will write my considerations below. In case of somebody points to the error, I will fix the calculator logic.
We have CaCl2 ppm. Most likely, it is mass concentration, defined as the ratio of the mass of solute in milligrams to the mass of solution in kilograms.
We need to find out chlorides WPS ppm. Similarly, chlorides water phase salinity will be defined as the ratio of the mass of chlorine ions in milligrams to the mass of solution in kilograms.
If we divide first formula to the second, and move CaCl2 ppm to the right, we will get
Thus, we only need to find out the ratio of chlorine ions mass to calcium chloride mass.
One mole of calcium chloride consists of one mole of calcium and two moles of chlorine. One mole of calcium weights 40.078g, one mole of chlorine weights 35.453g, and one mole of calcium chloride weights 110,98g
Hence, ratio will be
And final conversion formula will be
The calculator below uses this formula.