NCERT Class XII Chemistry
Chapter - Solutions
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Question : 45
Total: 53
Calculate the mass of urea (NH2CONH2) required in making 2.5 kg of 0.25 molal aqueous solution.
Solution:  
Moles of urea =0.25mole
Mass of solvent (water) =1kg=1000g
Molar mass of urea ( NH2CONH2 ) =14+2+12+16+14+2 =60g mol1
Mass of urea in 1000 g of water =0.25mol×60g mol1=15 g
Total mass of solution =1000+15 g=1015 g=1.015 kg
Thus, 1.015 kg of solution contain urea =15 g
2.5kg of solution will require urea =
15g
1.015kg
×2.5kg
=37g
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