What is the molality of lead nitrate?

Question

in 0.726 M Pb(NO3)2 (density=1.202 g/mL)?

Answer 1

take a litre @ (density=1.202 g/mL) = 1,202 grams per litre

take 0.726 M Pb(NO3)2  that's 0.726 moles of Pb(NO3)2 in that litre, & using the molar mass of Pb(NO3)2 , find its grams:

0.726 M Pb(NO3)2 @ 331.2 g/mol = 240.45 grams of Pb(NO3)2

which means that out of that one litre's 1202 grams , 240.45 is Pb(NO3)2 & the rest is water = 961.55 grams of water

since molality is the moles of solute per kilogram of solvent, let's set that up:

0.726 moles Pb(NO3)2 / 0.96155 kg solvent = 0.755

your answer is : 0.755 molal