Question

Calculate the mass of urea nh2conh2 required in making 2.5 kg of 0.25 molal aqueous solution

Answer 1

hello friend...
I am trying to solve your question..

first of all we have to find out the molar mass of urea.
molar mass of urea = 60 g/mole

0.25 molar aqueous solution of urea --- 1000g of water contains 0.25 mole of urea. so we get 0.25 × 60 = 15 g of urea.
Now,
(1000+15)g of solution contains 15g urea = {15 × (2.5×1000)} ÷ {1000+15}
then we get approx 37gram.

hope it will help you.

Answer 2

Hey !!

Mass of required aqueous solution = 2.5 kg = 2500 g

0.25 molal aqueous solution of urea it means that 0.25 mole of urea is dissolved in 1000 grams of water.

Mass of water = 1000 g

Mass of urea = 0.25 mol

Molar mass of urea (H₂NCONH₂) = 4 × 1 + 2 × 14 + 1 × 12 + 1 × 16 = 60 g mol⁻¹

        NOTE :- Mass of urea = Number of moles of urea × Molar mass of urea  

     Mass of 0.25 moles of urea = 0.25 mol ×× 60 h mol⁻¹ = 15 g

Mass of solution = 1000 g + 15 g = 1015 g

1015 g of aqueous solution contains urea = 15 g

∴ 2500 g of aqueous solution will require urea  

         = 15 g / 1015 kg × 2500 g  

            = 36.95 g

HOPE IT HELPS YOU !!