Ion concentration refers to the molar concentration of an ion in solution. It may be identical to, or greater or less than, the molar concentration of the compound containing the ion that was used to make the solution. For soluble salts, the molarity of a particular ion is equal to the molarity of that compound times the subscript for that ion. For example, 1 M of AlCl3 is 1 M in Al3+ and 3 M in Cl−. 1 M of (NH4)2SO4 is 2 M in NH4+ and 1 M in SO42−. 1: What is the concentration of K+ in 0.15 M of K2S?

2: If CaCl2 is dissolved in water, what can be said about the concentration of the Ca2+ ion?

3: A scientist wants to make a solution of tribasic sodium phosphate, Na3PO4, for a laboratory experiment. How many grams of Na3PO4 will be needed to produce 275 mL of a solution that has a concentration of Na+ ions of 1.20 M ?