Calculate the mass of Urea ( NH2CONH2) required in making 2.5 kg of 0.25 molal aqueous solution .
Mass of required aqueous solution = 2.5 kg = 2500g 0.25 molal aqueous solution of urea means 0.25 mole of urea is dissolved in 1000 g of water. Mass of water = 1000g Moles of urea= 0.25 Mol Molar mass of urea ( NH2CONH2) = 4×1+2×14+1×12+1×16 = 60 g mol-1 mass of urea = Number of moles of urea × Molar mass of urea Mass of 0.25 moles of urea = 0.25 mol× 60gmol-1 = 15 g Mass of solution = 1000g+15g= 1015g 1015 g of aqueous sol contains urea = 15g 2500g of aqueous sol will require urea = 15g/ 1015 kg × 2500g= 36.95g Ans