To prepare a solution of Lead (II) nitrate, first we have to deal with the calculations.
Since the concentration is given, we can start from that point.
Concentration = moles of solute/Volume of the solution (L)
Concentration = 0.25 mol/L
Volume = (150/1000)L = .15L
By arranging the formula we can have:
moles of solute = Concentration * Volume
moles of solute = 0.25 * .15
moles of solute = 0.0375 moles Lead (II) nitrate
Next we convert the moles of Lead (II) nitrate (Pb(NO3)2) to mass. We can do that by multiplying the moles with the molar mass of Pb(NO3)2
mass Pb(NO3)2 = 0.0375mol * 331.2 g/mol
mass Pb(NO3)2 = 12.42 grams Pb(NO3)2
In preparing the solution, first, measure or weigh 12.42 grams of Pb(NO3)2. Transfer the measured mass in a flask and add water until it reaches the 150mL mark.