The mole fraction of an aqueous solution of magnesium chlorate is 0.371. Calculate the molarity (in mol/L) of the magnesium chlorate solution, if the density of the solution is 1.39 g mL-1.

Answer 1

Take 1 mol of solution; you will have 0.371 mol Mg(ClO3)2 + 0.629 mol H2O.
.371 mol Mg(ClO3)2 x molar mass = ? g Mg(ClO3)2
0.629 mol H2O x molar mass H2O = ? g H2O

The solution consists of about 71 g Mg(ClO3)2--that's an estimate-- in 71+about 11 g H2O for a total of about 82 g. What is the volume of that?
volume = mass/density = about 82/1.39 = about 60 mL or 0.060L
You want molarity which is M = moles/L. You know mols (0.371) and you know L, that gives you M.