Freezing Point Depression Calculator
Calculate freezing point depression and new freezing point using molality and van't Hoff factor
Calculate Freezing Point Depression
Moles of solute per kilogram of solvent
Kf = 1.86 °C·kg/mol, Tf° = 0°C
Freezing Point Depression Results
Formula: ΔTf = i × Kf × m
Calculation: 1 × 1.86 × 0 = 0.00°C
Analysis:
Example Calculation
Antifreeze Solution Example
Problem: Calculate the freezing point of a 0.4 m solution of ethylene glycol in water
Given: Molality (m) = 0.4 mol/kg, Kf for water = 1.86 °C·kg/mol
Solute: Ethylene glycol (C₂H₆O₂) - non-electrolyte, so i = 1
Pure water freezing point: 0°C
Calculation Steps
1. ΔTf = i × Kf × m
2. ΔTf = 1 × 1.86 × 0.4
3. ΔTf = 0.74°C
4. New freezing point = 0°C - 0.74°C = -0.74°C
Quick Examples
Road Salt (NaCl)
1.0 m NaCl in water
ΔTf ≈ 3.5°C (i = 1.9)
New freezing point: -3.5°C
Sugar Solution
0.5 m sugar in water
ΔTf = 0.93°C (i = 1)
New freezing point: -0.93°C
Calcium Chloride
0.5 m CaCl₂ in water
ΔTf ≈ 2.7°C (i = 2.9)
More effective than NaCl
Common Solvents
van't Hoff Factors
Understanding Freezing Point Depression
What is Freezing Point Depression?
Freezing point depression is a colligative property that occurs when a nonvolatile solute is added to a pure solvent. The freezing point of the solution becomes lower than that of the pure solvent. This phenomenon is directly related to the concentration of solute particles in the solution.
Key Concepts
- •Colligative property - depends on particle concentration, not identity
- •Greater molality = greater freezing point depression
- •Electrolytes produce more particles than non-electrolytes
- •Each solvent has a unique cryoscopic constant (Kf)
Formula and Calculations
Basic Formula
ΔTf = i × Kf × m
ΔTf = freezing point depression (°C)
i = van't Hoff factor (particles per formula unit)
Kf = cryoscopic constant (°C·kg/mol)
m = molality (mol solute/kg solvent)
New Freezing Point
Tf(solution) = Tf°(pure) - ΔTf
The solution always freezes at a lower temperature
van't Hoff Factor
Non-electrolytes: i = 1
Strong electrolytes: i = number of ions
Actual values are often less than theoretical
Real-World Applications
Road De-icing
Salt (NaCl) and calcium chloride (CaCl₂) are spread on roads to lower the freezing point of water, preventing ice formation.
Antifreeze
Ethylene glycol in car radiators prevents coolant from freezing in winter temperatures.
Food Science
Sugar and salt in ice cream prevent it from freezing solid, maintaining a scoopable texture.