By Claire Gillespie, Updated Mar 24, 2022

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Freezing Point

The temperature at which a liquid turns into a solid is called its freezing point. For pure water, this is 32°F (0°C). At this temperature, water molecules and ice molecules are in dynamic equilibrium—water freezes while ice melts at the same rate.

Water Molecules

A water molecule is composed of one oxygen atom and two hydrogen atoms. When the temperature drops, the kinetic energy of these molecules decreases, allowing them to form hydrogen bonds that create a crystalline lattice known as ice.

Adding Sugar to Water

When sugar (sucrose) dissolves in water, the sugar molecules become dispersed throughout the solvent. They interfere with the ability of water molecules to align into the regular hydrogen‑bonded structure required for ice formation. The sugar molecules occupy space that would otherwise be available to water, effectively “crowding” the solution.

Freezing Point Depression

Because sugar particles remain in the liquid phase, they lower the chemical potential of the solution. This phenomenon, known as freezing point depression, means the mixture must be cooled below 32°F (0°C) before ice can form. The extent of the depression depends on the concentration of sugar: a higher amount of dissolved sugar leads to a greater drop in freezing temperature.

In practice, this is why sugary drinks and desserts remain liquid at temperatures that would freeze plain water. The principle is widely applied in food preservation and in creating ice‑cream bases that maintain a desirable texture.