Evian mineral water contains (among other ions) Ca2+ (80 ppm) and Mg2- (26 ppm).

Question

Evian mineral water contains (among other ions) Ca2+ (80 ppm) and Mg2- (26 ppm).

a) What mass in grams, of each of these ions is present in a 0.750 L bottle of Evian

b) Suppose you tried to "make" Evian by dissolving minerals in the appropriate concentrations in pure water. If MgCl2 and CaCl2 are your sources for these ionsm what mass of each salt (in grams) is needed to produce the ion concentrations above? Assume you are making a 0.750 L sample.

c) What is the concentration, in M, of the chloride ion, Cl-, in your prepared Evian?

Explanation / Answer

a)

Ca2+ = 80ppm; Mg2+= 26ppm

1ppm= 1*10-3 g in 1L of solvent.

80 ppm = 80*10-3 g in 1L of water

80 ppm of Ca2+ in 0.750L of water = (80*10-3 )/0.750 =106*10-3 g

26 ppm of Mg2+ in 0.750L of water = (26*10-3)/0.750 =34.6*10-3 g

b) Masses of MgCl2 and CaCl2 needed to mix = 106*10-3 g of CaCl2 and 34.6*10-3 g of MgCl2

c) concentration of Cl- ion = 106*10-3 + 34.6*10-3 =140.6*10-3 g in 0.750 L of water.

Atomic weight of Cl= 35.5 g

Molarity = number of moles of the substance in 1L of solution

= (140.6*10-3)/(35.5*0.750)

=5.28*10-3 M

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