Water always boils at 100 °C, right? Not always! Water boils at 100 °C at 1 atmosphere of pressure. Every liquid boils at the temperature at which its vapor pressure equals the pressure above its surface. Change the pressure and the required boiling temperature changes! Explore both phase change and vapor pressure in this very dramatic demonstration. By decreasing the vapor pressure inside the syringe, hot water can be boiled at less than 100 °C. As the water boils, the vapor is pressurizing the area above the liquid. The water will continue to boil until the pressure equals that of the vapor pressure or until no liquid is left. Includes Teacher Demonstration Notes, reproducible student handouts, and a detailed discussion section. All materials included are reusable.
Concepts: Vapor pressure, boiling, phase change.
Time Required: 10 minutes
Materials Provided: Demonstration syringe (140-mL) and stopcock with Luer Lock adapter.
Boiling in a Syringe Video
Water in a sealed syringe boils easily as the plunger is withdrawn and the pressure decreases. Boiling point depends on pressure!
Flinn Catalog/Reference Manual Page 381
Flinn Middle School Catalog/Reference Manual Page 359
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