Moles chemistry?

Question

Calculate the mass of solute required to prepare ib the solution

200cm^3 of solution containig 0.50 mol dm ^-3 cl-iond prepared by dissolving cacl2.6h2o in water.

Answer 1

0.50 mol/dm^3 = 0.5 M
200 cc = 0.2 L = 0.2 dm^3
mols you want Cl^- = M x L = 0.5 x 0.2 = 0.1 mol Cl^-

Convert mols Cl^- to mols CaCl2.
0.1 mol Cl^- x (1 mol CaCl2/2 mols Cl^-) = 0.05 mol CaCl2.

Now convert mols CaCl2 to grams.
mols = grams/molar mass. You kow mols and molar mass, substitute and solve for grams CaCl2.