Question

Calculate the mass of urea (NH2CONH2) required in making 2.5 kg of 0.25 molal aqueous solution.

Answer in attachment​

Answer 1

Answer:

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Explanation:

0.25 molal aqueous solution of urea means that

0.25 mole of urea are present in 1 kg of water  

Moles of urea = 0.25mole 

Mass of solvent (water) = 1 kg = 1000 g 

Molar mass of urea (NH2CONH2) = 60 g mol

1. 0.25moleofurea=0.25mol×60gmol1=15g 

Totalmassofsolution=1000+15g=1015g=1.015kg

 Thus; 1.015 kg of solution contain urea

= 15g×2.5kg of solution will require urea

1.015kg15g×2.5kg = 37 g 

Answer 2

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°°° Solution °°°

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0.25 molal aqueous solution of urea means that 0.25 mole of urea are present in 1 kg of water  

Moles of urea = 0.25mole 

Mass of solvent (water) = 1 kg = 1000 g 

Molar mass of urea (NH2CONH2) = 60 g mol

1. 0.25moleofurea=0.25mol×60gmol1=15g 

Totalmassofsolution=1000+15g=1015g=1.015kg

 Thus; 1.015 kg of solution contain urea = 15g×2.5kg of solution will require urea

1.015kg15g×2.5kg = 37 g 

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