What mass in grams of a molecular substance (molar mass = 50.0 g/mol) must be added to 500 g of water to produce a solution that boils at 101.56°C? [Kb(water) = 0.512°C m-1]

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Quizplus · Accepted Answer

The boiling point elevation formula is ΔTb = i * Kb * m, where ΔTb is the change in boiling point, i is the van't Hoff factor (1 for non-electrolytes), Kb is the ebullioscopic constant, and m is the molality. The change in boiling point is 101.56°C - 100°C = 1.56°C. Solving for molality (m) gives m = 1.56 / 0.512 = 3.05 mol/kg. Since the solution is 500 g of water (0.5 kg), the moles of solute needed is 3.05 mol/kg * 0.5 kg = 1.525 mol. The mass of the solute is 1.525 mol * 50.0 g/mol = 76.25 g, which rounds to 76.2 g.

What Mass in Grams of a Molecular Substance (Molar Mass