A 0.9182 g sample of CaBr2 is dissolved in enough water to give 500 ml of solution. what is the calcium ion concentration in this solution

First calculate the number of moles of CaBr2 given the molar mass of 199.89 g/mol.

moles CaBr2 = 0.9182 g / (199.89 g / mol) = 4.60 x 10^-3 mol

We see that each CaBr2 contains only 1 mole of Ca, so the moles of Ca is also:

moles Ca + = 4.60 x 10^-3 mol

So the molarity of this is:

Molarity Ca + = 4.60 x 10^-3 mol / 0.500 L

Molarity Ca + = 9.19 x 10^-3 M