Enter your solution's Molality, choose a Solvent, and set the van't Hoff Factor (i) to calculate the Freezing Point Depression (ΔTf) — plus see the New Freezing Point and the Kf Value Used. Got a non-standard solvent? Drop in a Custom Kf Value and the calculator handles the rest.
Freezing Point Depression (ΔTf)
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New Freezing Point
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Kf Value Used
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Freezing point depression is the decrease in the freezing point of a solvent when a non-volatile solute is added. The solution always freezes at a lower temperature than the pure solvent due to the presence of solute particles that disrupt the crystal lattice formation.
Freezing point depression is calculated using the formula ΔTf = Kf × m × i, where Kf is the cryoscopic constant of the solvent, m is the molality of the solution, and i is the van't Hoff factor representing the number of particles formed per solute molecule.
The van't Hoff factor (i) represents the number of particles a solute forms when dissolved. For non-electrolytes like sugar, i = 1. For ionic compounds, i equals the number of ions formed (e.g., NaCl has i = 2, CaCl₂ has i = 3).
The cryoscopic constant (Kf) is a property specific to each solvent that indicates how much the freezing point decreases per molal concentration of solute. Water has Kf = 1.86 °C·kg/mol, while benzene has Kf = 5.12 °C·kg/mol.
Salt (sodium chloride) is used to de-ice roads because it dissociates into Na⁺ and Cl⁻ ions, lowering the freezing point of water. This prevents ice formation at temperatures below 0°C, keeping roads safer for driving in winter conditions.
Molality (m) is moles of solute per kilogram of solvent, while molarity (M) is moles of solute per liter of solution. Molality is used in freezing point depression calculations because it doesn't change with temperature, unlike molarity.
Yes, by measuring the freezing point depression of a solution with a known mass of unknown solute, you can calculate the molar mass using the relationship between ΔTf, molality, and the number of moles of solute.