Question

What is the molal of 0.726 M lead nitrate? The density of the solution is 1.202 g/ml

Answer 1

0.726 M Pb(NO3)2 = 0.726 mols/L of solution.

molar mass Pb(NO3)2 is 331.2 grams. We have 331.2g/mol x 0.726 moles = 240.4 grams Pb(NO3)2. That is in1,000 mL of solution.
The mass of that 1,000 mL is mass = volume x density = 1,000 mL x 1.202 g/mL = 1202 grams. 240.4 g of that is Pb(NO3)2 and the remainder is water as solvent. So 1202 g - 240.4 g = 961.6 g which is the mass of the solvent. Since molality = m = mols/kg solvent that will be m = 0.726 g/0.9616 kg = ? molal
Check those numbers before you take them to the bank.