Question

The following replicate values were reported for the concentration of magnesium chloride, MgCl2, in mol/L. What value should be reported as the mean concentration of the chloride ion, Cl-, converted to ppm? (You may use the simplified definition of ppm.)
0.00141, 0.00138, 0.00175, 0.00134, 0.00132 F MgCl2

Answer 1

mean M = sum of M/5 = ?
Then mean M x molar mass = grams/L.
Change that to mg/L and that is ppm.

Answer 2

there are about 55.3 moles of water in a liter

the mean (average) concentration of chloride ions will be twice the arithmetic average of the MgCl2 concentrations (two Cl- for each MgCl2)

I would be tempted to disregard the 175 value as a "flier"...but that's up to you

divide the average concentration by 55.3 (to get moles per mole), and multiply the result by a million to get ppm

Answer 3

To clarify, I gave you ppm MgCl2 so ppm Cl^- is twice ppm for the MgCl2 "molecule". Like Scott, I too would consider throwing out the 175 value but as I re-read the question I don't think that is an option.