What is the meaning of #"parts per million concentration"#? If the concentration is #"250 ppm"# with respect to #NaCl#, what are the concentrations of sodium and chloride ions?

1 Answer
anor277
Aug 21, 2017

#1*"ppm"-=1*mg*L^-1#

Explanation:

With these dilutions, normally we do not have to consider densities of the solution versus the solvent.

And thus a #250*"ppm"# solution represents #250*mg# dissolved in #1*L# of water. And thus #0.250*g# is dissolved in one litre of water.

Given #1*"ppm"-=1*mg*L^-1#, there are #1000xx1000*mg# WATER, i.e. #999,999*mg# per milligram of solvent, hence #"parts per million"#.

Of course this value represents the concentration of #NaCl# NOT of #Cl^-# ion. Since chlorine constitutes 61% by mass of the solute, we may need to modify the given values appropriately.

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