how would you prepare 300 ml of a 10% CaCl2 solution (w/w)?

Answer 1

What's the density of 10%CaCl2?
You would want 30 g CaCl2/300 g soln but that isn't 300 mL. That would be 300 g CaCl2 in 270 g H2O and that will produce a volume that is probably about 280 mL.