1.20 L of a solution that is 15.0 % of Pb(NO3)2 by mass (the density of the solution is 1.16 g/mL), starting with solid solute. how would you prepare this?

Answer 1

You want 1.2L or 1200 mL.
mass = volume x density = 1200 x 1.15 = approx 1400 grams. Remember to redo these calculations with more accuracy than my estimates.
To make 15% solution you need 15 g Pb(NO3)2 in 100 g solution. So for 1400 g solution you will need
15 g x 1400/100 = approx 210 g Pb(NO3)2.
Weigh out approx 210 g Pb(NO3)2 and add enough water to make a total of approx 1400 g.