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

mean M = sum of M/5 = ?

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

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

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.

To calculate the mean concentration of the chloride ion, Cl-, converted to ppm, you will need to follow these steps:

1. Convert each concentration of MgCl2 from mol/L to ppm. The conversion factor for converting from mol/L to ppm is 1 ppm = 1 mg/L.

Concentration 1: 0.00141 mol/L = 0.00141 * 1000 mg/L = 1.41 mg/L
Concentration 2: 0.00138 mol/L = 0.00138 * 1000 mg/L = 1.38 mg/L
Concentration 3: 0.00175 mol/L = 0.00175 * 1000 mg/L = 1.75 mg/L
Concentration 4: 0.00134 mol/L = 0.00134 * 1000 mg/L = 1.34 mg/L
Concentration 5: 0.00132 mol/L = 0.00132 * 1000 mg/L = 1.32 mg/L

2. Calculate the mean concentration by adding up all the converted values and dividing by the number of values.

Mean concentration = (1.41 + 1.38 + 1.75 + 1.34 + 1.32) / 5 = 1.42 mg/L

3. Convert the mean concentration from mg/L to ppm.

Since the simplified definition of ppm states that 1 ppm = 1 mg/L, the mean concentration of 1.42 mg/L is equal to 1.42 ppm.

Therefore, the mean concentration of the chloride ion, Cl-, converted to ppm, should be reported as 1.42 ppm.