Practicing Success
Calculate the mass of urea (NH2CONH2) required in making 2.5 kg of 0.25 molal aqueous solution. |
32 g 37 g 42 g 50 g |
37 g |
0.25 molal aqueous solution of urea means that 0.25 mole of urea are present in 1 kg of water Moles of urea = 0.25 mole
Mass of solvent (water) = 1 kg = 1000 g
Molar mass of urea (NH2CONH2) = 60 g mol-1
0.25 mole of urea = 0.25mol × 60 g mol-1 = 15 g
Total mass of solution = 1000 + 15 g = 1015 g = 1.015 kg
Thus; 1.015 kg of solution contain urea = 15 g
1 kg of the solution contains urea = \(\frac{15}{1.015}\)
2.5kg of solution will require urea = \(\frac{15}{1.015}\) x 2.5 = 37 g
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