The concentration may be expressed as % m/m, this is the mass of ions in 100 mass units of solution, whose formula is:
% m/m = [mass of ions / mass of solution]*100
Then,
%m/m = [8.5*10^ -3 grams of calcium ions] / [490 grams of solution] * 100 =
% m/m = 1.74 * 10^ -5 %
Answer: 1.74 * 10 ^ -5 %
