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Calculate the mass of urea (NH_2CONH_2) required in making 2.5 kg of 0.25 molal aqueous solution.

2.4   Calculate the mass of urea  (NH_{2}CONH_{2})  required in making  2.5 \; kg  of  0.25\; molal  aqueous solution.

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Let us assume that the mass of urea required be x g.

So moles of urea will be :

                                                 Moles = \frac{Given\ mass}{Molar\ mass} = \frac{x}{60}\ moles

                                                 Molality = \frac{Moles}{Mass\ of\ solvent\ in\ Kg} = \frac{\frac{x}{60}}{2.5-0.001x} = 0.25

                                                 we get      x =  37

Thus mass of urea required = 37 g.

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