If the freezing point of pure water is 0 °C, what will be the freezing point of
Practice Questions
Q1
If the freezing point of pure water is 0 °C, what will be the freezing point of a solution containing 1 mole of NaCl in 1 kg of water? (2023)
-1.86 °C
-3.72 °C
-2.26 °C
-0.93 °C
Questions & Step-by-Step Solutions
If the freezing point of pure water is 0 °C, what will be the freezing point of a solution containing 1 mole of NaCl in 1 kg of water? (2023)
Step 1: Understand that the freezing point of pure water is 0 °C.
Step 2: Know that when a solute (like NaCl) is added to water, it lowers the freezing point. This is called freezing point depression.
Step 3: Identify the formula for freezing point depression: ΔTf = i * Kf * m.
Step 4: Determine the values needed for the formula: i (van 't Hoff factor for NaCl) = 2 (because NaCl dissociates into Na+ and Cl-), Kf (freezing point depression constant for water) = 1.86 °C kg/mol, and m (molality) = 1 mol/kg.
Step 5: Plug the values into the formula: ΔTf = 2 * 1.86 °C kg/mol * 1 mol/kg.
Step 6: Calculate ΔTf: 2 * 1.86 = 3.72 °C.
Step 7: Find the new freezing point by subtracting the depression from the original freezing point: 0 °C - 3.72 °C = -3.72 °C.
Step 8: Conclude that the freezing point of the solution is -3.72 °C.
Freezing Point Depression – The phenomenon where the freezing point of a solvent is lowered by the addition of a solute.
Colligative Properties – Properties that depend on the number of solute particles in a solution, not the identity of the solute.
Van't Hoff Factor (i) – A factor that accounts for the number of particles the solute dissociates into; for NaCl, i = 2.
Molality (m) – A measure of the concentration of a solution expressed as moles of solute per kilogram of solvent.
