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Malti❄️ Freezing Point Depression & Boiling Point Elevation
Dissolve a solute and watch both the freezing point drop and boiling point rise by the same colligative-properties physics. Cool the solution and see freeze-concentration push solute into the shrinking liquid.
How it Works
When a solute dissolves in a solvent, it lowers the solvent's chemical potential in the liquid phase, which shifts both phase boundaries: the freezing point drops and the boiling point rises. Both shifts are proportional to the molality of dissolved particles (not the solute's identity) and to the van't Hoff factor i, which accounts for how many particles each formula unit produces when it dissolves.
The left panel plots a temperature scale marking the pure solvent's freezing point Tf0 and boiling point Tb0 against the shifted solution values Tf0 − ΔTf and Tb0 + ΔTb. The right panel animates what happens at the particle level as you cool the solution: solvent molecules crystallize into an orderly solid once the temperature reaches the (possibly depressed) freezing point, while solute particles are excluded from the growing solid and crowd into the shrinking remaining liquid — a real effect called freeze-concentration that further depresses the local freezing point of what's left, causing freezing to self-limit unless you keep cooling.
ΔTb = i·Kb·m (boiling point elevation)
New Tf = Tf0 − ΔTf New Tb = Tb0 + ΔTb
Water: Kf = 1.86 °C·kg/mol, Kb = 0.512 °C·kg/mol, Tf0 = 0°C, Tb0 = 100°C
Benzene: Kf = 5.12 °C·kg/mol, Kb = 2.53 °C·kg/mol, Tf0 = 5.5°C, Tb0 = 80.1°C
Frequently Asked Questions
What are colligative properties, and why do they depend only on the number of dissolved particles?
Colligative properties (freezing point depression, boiling point elevation, vapor pressure lowering, and osmotic pressure) all arise because dissolved solute particles lower the chemical potential (and entropy of mixing) of the solvent, regardless of what the solute actually is. Only the number of dissolved particles per kilogram of solvent matters, not their identity, size, or charge.
What do the formulas ΔTf = i·Kf·m and ΔTb = i·Kb·m mean?
ΔTf is how far the freezing point drops and ΔTb is how far the boiling point rises. m is the molality (moles of solute per kilogram of solvent), i is the van't Hoff factor, and Kf/Kb are the cryoscopic and ebullioscopic constants — solvent-specific proportionality constants that convert molality into a temperature shift.
Why does the van't Hoff factor i matter?
i counts how many particles one formula unit of solute actually produces in solution. Glucose does not dissociate, so i = 1. NaCl splits into Na⁺ and Cl⁻, so i = 2. CaCl₂ splits into one Ca²⁺ and two Cl⁻, so i = 3. A higher i produces a proportionally larger colligative effect per mole dissolved.
What is freeze-concentration, and why does it matter?
As a solution cools and pure solvent crystallizes out into ice, the solute is largely excluded from the growing solid. The remaining liquid shrinks but keeps almost all the original solute, so its concentration rises — further depressing its local freezing point. This is why sea ice is largely fresh water while the leftover brine grows saltier.
Why does road salt melt ice and snow?
Salt dissolves into the thin liquid layer on ice, and because NaCl has i = 2, it strongly depresses the local freezing point below the ambient temperature, so the ice can no longer stay solid there and melts.
How does antifreeze/coolant protect a car engine?
Ethylene glycol antifreeze depresses the coolant's freezing point so it doesn't turn to ice and crack the engine block in cold weather, and raises its boiling point so it doesn't boil over in hot weather — both from the same dissolved solute.
How can freezing-point depression measure an unknown solute's molar mass?
By dissolving a known mass of an unknown solute in a known mass of solvent and measuring ΔTf, you can solve for molality m, back-calculate moles of solute, and hence its molar mass — a classic technique called cryoscopy.
Why is salt used in traditional ice-cream making?
Packing salt around an ice bath depresses the brine's freezing point well below 0°C, so the brine stays liquid and cold enough to pull heat out of the cream mixture fast enough to freeze it.
How does this relate to osmotic pressure?
Osmotic pressure follows the analogous van't Hoff equation Π = iMRT, using the exact same particle-counting logic and the same i factor that scales ΔTf and ΔTb.
About this simulation
This simulator pairs a phase-boundary diagram with a particle-level cooling animation to show why dissolving something in water both lowers its freezing point and raises its boiling point — and why both shifts obey the exact same physics. Drag the molality slider, pick a van't Hoff factor, and hit Cool Down to watch solvent molecules crystallize into an orderly solid while excluded solute crowds into the shrinking liquid, a real phenomenon called freeze-concentration that keeps depressing the local freezing point of what's left.
🔬 What it shows
Two synchronized views: a temperature-scale diagram marking the pure solvent's Tf0/Tb0 against the shifted solution values Tf0−ΔTf and Tb0+ΔTb, and an animated container where solvent particles freeze into a growing solid while solute particles are pushed into the shrinking liquid.
🎮 How to use
Set molality m and van't Hoff factor i (glucose, NaCl, or CaCl₂), choose water or benzene as the solvent, then click Cool Down to animate cooling and watch freezing begin once the temperature reaches the (possibly depressed) freezing point. Reset returns everything to the default water/glucose scenario.
💡 Did you know?
Freeze-concentration is self-limiting: as ice forms, the remaining brine gets more concentrated and its local freezing point keeps dropping, so freezing pauses unless you keep lowering the temperature — the same reason sea ice stays largely fresh while the ocean beneath gets saltier.
Frequently asked questions
What does the left phase-boundary panel show?
It plots a vertical temperature scale marking the pure solvent's freezing point Tf0 and boiling point Tb0 (blue dashed lines) against the shifted solution values Tf0 − ΔTf and Tb0 + ΔTb (orange lines), with the shift amounts labeled so you can see both effects at a glance.
What does the right particle panel show?
It's an animated container of blue solvent particles and orange solute particles. When you click Cool Down, the simulated temperature falls; once it reaches the local freezing point, solvent particles lock into an ordered solid at the bottom while solute particles stay in the shrinking liquid above, visually demonstrating freeze-concentration.
How do I use the Cool Down button?
Click it to start lowering the simulated temperature over time. The stats box updates live with the current temperature, whether freezing has started, the local freezing point of the remaining liquid, and its effective molality as solute gets left behind by the growing solid.
Why does freezing seem to pause partway through?
As solvent freezes out, the leftover liquid's solute concentration rises, which drops its local freezing point further below the current temperature. Freezing then stalls until you cool further — a direct visualization of the freeze-concentration feedback loop.
What do the water and benzene presets change?
Each solvent has its own cryoscopic and ebullioscopic constants (Kf, Kb) and its own pure freezing/boiling points, so the same molality and van't Hoff factor produce different absolute temperature shifts depending on which solvent you pick.
What's the difference between choosing i = 1, 2, or 3?
i reflects how many particles one dissolved formula unit produces: glucose stays as one molecule (i = 1), NaCl dissociates into two ions (i = 2), and CaCl₂ dissociates into three ions (i = 3) — so at the same molality, CaCl₂ produces roughly three times the freezing-point depression and boiling-point elevation of glucose.
Dissolve a solute and watch both the freezing point drop and boiling point rise by the same colligative-properties physics. Cool the solution and see freeze-concentration push solute into the shrinking liquid.
2D · HTML5 Canvas 2D · 60 FPS target · runs fully client-side, no install