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Q1. What mass of ethylene glycol (C2H6O2), in grams, must be added to 1.0 kg of water to produce a solution that boils at 105.0 °C?
What you'll need:
Molality: ((moles of solute (mol))/(mass of solvent (kg))→m)
Molar mass of C_2 H_6 O_2 is (62.07 g∕mL)
Boiling Point Elevation: (ΔT_b=m×K_b )
K_b of water: 0.512 (°C)/m
Q2. Calculate the boiling point of a 3.60 m aqueous sucrose solution.
To solve this problem, use the boiling-point elevation equation to calculate the desired molality of the solution from ΔTb.
Then use that molality to determine how many moles of ethylene glycol are needed per kilogram of water. Finally, calculate the molar mass of ethylene glycol and use it to convert from moles of ethylene glycol to mass of ethylene glycol.
C2H6O2 molar mass = 62.07 g/mol
ΔTb = m × Kb (boiling point elevation)
Begin by solving the boiling point elevation equation for molality and substituting the required quantities to calculate m.
The units of the answer are correct. The magnitude might seem a little high initially, but the boiling point elevation constant is so small that a lot of solute is required to raise the boiling point by a small amount.
