what mass of cacl2 (in g) should the chemist use?
if he wants to make 5.5 L of a 0.250 M CaCl2 solution.
5.5 Liters of a 0.250 mol/L solution will contain:
(0.250 mol CaCl2/L soln) × 5.5 L soln = 1.375 mol CaCl2.
Now, we need to convert mols to grams. For that, use the periodic table of elements.
Get the molar mass of calcium chloride by adding up the molar masses of each atom (1 calcium and 2 chlorines)
Ca = 40.078 g/mol, Cl = 35.4527 g/mol
Thus CaCl2 = 40.078 + 2×35.4527 = 110.98 g CaCl2 / mol CaCl2
Now, use this conversion factor on the answer above:
1.375 mol CaCl2 × (110.98 g CaCl2 / mol CaCl2) = 152.60 g CaCl2
The proper answer is 150 g CaCl2 (2 significant digits)