Estimate the Mass of Urea- Required in Making 2.5 Kg of 0.25 Molal Aqueous Solution: Urea (For CBSE, ICSE, IAS, NET, NRA 2022)

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Urea

  • Urea is a nitrogenous compound containing a carbonyl group attached to two amine groups with osmotic diuretic activity.
  • Urea, also called carbamide, the diamide of carbonic acid.
  • Its formula is
  • Urea has important uses as a fertilizer and feed supplement, as well as a starting material for the manufacture of plastics and drugs.
  • A colourless, crystalline substance melts at and decomposes before boiling.
  • Urea is used to treat dry/rough skin conditions (e. g. , eczema, psoriasis, corns, and callus) and some nail problems (e. g. , ingrown nails) .
  • It may also be used to help remove dead tissue in some wounds to help wound healing.

Molality

= molality

Mol = moles of solute

Kg = kilograms of solvent

  • Molality is a property of a solution and is defined as the number of moles of solute per kilogram of solvent.
  • Molality is a measure of number of moles of solute present in 1 kg of solvent.
  • This contrasts with the definition of molarity which is based on a specified volume of solution.
  • A commonly used unit for molality in chemistry is mol/kg. A solution of concentration 1 mol/kg is also sometimes denoted as 1 molal.
  • The SI unit for molality is mol/kg. A solution with a molality of 3 mol/kg is often described as β€œ3 molal” or β€œ3 m.”
  • So, following the SI system of units, mol/kg or a related SI unit is now preferred.

Mass of Urea

  • Mass of solution = 2.5 Kg
  • Molality = 0.25 m
  • Molar mass of urea ()

  • Mass of urea = Number of moles of urea Γ— Molar mass of urea
  • Mass of 0.25 moles of urea
  • Mass of solution = 1000 g + 15 g = 1015 g
  • 1015 g of aqueous solution contains urea

∴ 2500 g of aqueous solution will require urea

Mass of urea required in making 25 grams of 0.25 m = 37 grams

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