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

To calculate the mass of urea required for a 0.25 molal aqueous solution in 2.5 kg of water, follow these steps:

Formula for Molality:

Molality (m): m = moles of solute / mass of solvent (in kg)

Step 1: Find moles of solute

Rearrange the formula to calculate moles of solute: Moles of solute = Molality × Mass of solvent (in kg)

Calculation: Moles of urea = 0.25 mol/kg × 2.5 kg = 0.625 mol

Step 2: Calculate the mass of urea using its molar mass

The molar mass of urea (NH₂CONH₂) is calculated as: 
Molar mass = 14 + (1 × 2) + 12 + 16 + (1 × 2) = 60 g/mol

Mass of urea:

• Mass of urea = Moles × Molar mass
• Mass of urea = 0.625 mol × 60 g/mol = 37.5 g

Final Answer:

37 g