How to Determine a Boiling Point of Liquids

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When a liquid is heated it changes from its solid state into its gaseous state. The temperature at which this occurs is called the boiling point of the liquid.

Boiling points vary with the pressure of the environment around the liquid. A liquid at high pressure has a higher boiling point than a similar liquid at low pressure.

Typically, the boiling point of water is 100 degrees C (212 F). As it travels up or down mountains it may boil at lower temperatures because the pressure from the mountains is less than the atmospheric pressure at sea level.

The boiling point of a liquid is a characteristic property that helps to identify certain substances. It is also a useful property for separating and purifying volatile liquids, a process known as distillation.

How to Determine a Boiling Point of Liquids

To determine the boiling point of a liquid, an inverted glass capillary tube is filled with the liquid in question and allowed to cool. Then the vapor pressure of the liquid inside the capillary tube increases until it is equal to the atmospheric pressure outside. This forces the gaseous vapor to enter the tube and bubbles will begin to form.

The boiling point of liquids varies with their molecular weight and chemical structure. For example, acetone, which is a gas at room temperature and pressure, has a boiling point of 56degC (173 degF) while ethanol, which is liquid at room temperature and pressure, has a heating value of 78degC (173 degF). The boiling point of an organic compound is determined by the intermolecular forces that hold the molecules together and prevent them from escaping into the air.