What is the expected boiling point of a solution made by combining 400.0 g of water with 100.0 g of Na₂CO₃?

Question

Quizplus · Accepted Answer

The boiling point elevation formula is ΔTb = iKbm, where ΔTb is the boiling point elevation, i is the van't Hoff factor (number of particles the solute breaks into), Kb is the ebullioscopic constant of the solvent (water in this case, which is 0.512°C·kg/mol), and m is the molality of the solution. Na₂CO is sodium bicarbonate (NaHCO3), which dissociates into 2 particles (Na+ and HCO3-), so i = 2. The molar mass of NaHCO3 is approximately 84 g/mol. The molality (m) = moles of solute/kg of solvent = (100 g / 84 g/mol) / (400 g / 1000 g/kg) = 1.19 mol/kg. Thus, ΔTb = 2 * 0.512°C·kg/mol * 1.19 mol/kg = 1.22°C. The normal boiling point of water is 100°C, so the expected boiling point of the solution is 100°C + 1.22°C = 101.22°C, which rounds to 101.2°C, matching choice C. However, my initial selection was incorrect; the correct choice is C, not A.

What Is the Expected Boiling Point of a Solution Made