What Is the Freezing Point of Salol? Exact Answer

The freezing point of salol (phenyl salicylate) is 41.5 °C (106.7 °F). This is the temperature at which the solid and liquid forms of the compound exist in equilibrium under standard atmospheric pressure.

Why the Freezing Point Matters

Salol’s freezing point is a key physical constant used to identify the substance and check its purity. A sample that freezes at a lower temperature, or over a range of temperatures, likely contains impurities. This property is also useful in classroom demonstrations of supercooling. When liquid salol is cooled slowly, it can remain liquid well below 41.5 °C. Disturbing the liquid—by dropping in a small crystal of solid salol—triggers rapid crystallization, and the temperature jumps back up to the freezing point.

The behavior of small crystals is described by the Gibbs–Thomson equation, which notes that very small particles melt or freeze at a lower temperature than larger ones due to their high surface curvature Wikipedia. For a bulk sample of salol, the standard freezing point of 41.5 °C is the accepted reference value PubChem.

A quick example: if you heat salol to 50 °C to melt it completely, then let it cool in a clean container, it will typically stay liquid until you introduce a seed crystal. At that moment, the temperature will rise to 41.5 °C as the solid forms.

Key Takeaways

• The freezing point of salol is 41.5 °C (106.7 °F) at standard pressure.
• This value is used to confirm the identity and purity of the compound.
• Salol readily supercools, meaning it can remain liquid below its freezing point until crystallization is triggered.
• The Gibbs–Thomson effect explains why small crystals have a lower freezing point than bulk material, but the bulk freezing point remains 41.5 °C.