What mass of sodium chloride should be added to 500.0 g of water in order to decrease its freezing point to -1.0 °C? The K_f for water is 1.86°C/m.Consider if the solute is an electrolyte or a nonelectrolyte.

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Quizplus · Accepted Answer

Sodium chloride (NaCl) is an electrolyte and dissociates into two ions (Na+ and Cl-), so the van't Hoff factor (i) is 2. The freezing point depression formula is ΔTf = i * Kf * m. Rearranging for m (molality), we get m = ΔTf / (i * Kf). Substituting the values: m = 1.0 / (2 * 1.86) = 0.2688 mol/kg. For 500 g of water (0.5 kg), moles of NaCl needed = 0.2688 * 0.5 = 0.1344 mol. The molar mass of NaCl is 58.44 g/mol, so mass = 0.1344 * 58.44 = 7.85 g.

What Mass of Sodium Chloride Should Be Added to 500