1000 mL solution = 4.0 moles urea = 240 g urea
Since, mV= density (d)
∴ Mass =V×d
1000×d g solution =240 g urea
Solvent (H2O)=(1000 d−240)g=(1000 d−2401000) kg
Molality =4 mol×1000(1000 d−240) mol kg−1
Given, molality =4 mol kg−1
∴4000(1000 d−240)=4
=40004=(1000 d−240)
1000=1000 d−240
1000 d=1240
∴ d=1.24 g mL−1
Note: We can calculate density by the following relation,
Molality =1000×molarity(M)[1000 d−Mm1(molar mass)]