Why is a mixture of ice and water used in calibrating a thermometer instead of ice alone?

Using a mixture of ice and water to calibrate a thermometer is preferred because it establishes a reliable equilibrium temperature. When ice and water are combined, they form a stable state at 0°C (32°F) under standard atmospheric pressure, where the melting ice and the water coexist in equilibrium. This point is well-defined and reproducible, making it an ideal reference for calibrating thermometers.

If only ice were used, the thermometer could potentially measure temperatures that are not precisely defined due to variations in pressure or the specific properties of the ice itself. In contrast, the ice-water mixture provides a consistent and accurate point for calibration, ensuring that the thermometer readings are reliable and standardized. This is crucial in scientific measurements where precision is vital, as accurately determining the freezing point of water is essential for various experimental and industrial applications.