JoVE Lab Manual
Lab: Chemistry
Lab: Chemistry
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Boiling Points
Boiling Points
Learning Objectives
At the end of this lab, students should know...
What is the boiling point of a compound?
The boiling point of a compound is the temperature at which the transition from the liquid into the gas phase occurs. This occurs when the vapor pressure of the solution is equal to the atmospheric pressure.
What is vapor pressure?
Vapor pressure is the force of the gaseous phase on the liquid phase of a compound in a closed system at equilibrium.
How do intermolecular forces impact the boiling point?
The type and strength of the intermolecular forces determine the amount of energy required to break those attractive forces. As such, compounds that can hydrogen bond have higher boiling points than compounds that only interact through London dispersion forces.
How does volatility impact the boiling point?
Volatility is the tendency of a compound to vaporize spontaneously. The more volatile a substance, the lower its boiling point.
How is boiling point determined using the capillary method?
An inverted capillary is inserted into a test tube of the liquid of interest. When heated, the air in the capillary expands, and the vapor pressure of the liquid increases. As the air expands, it exits the capillary as a stream of bubbles. When the heat is removed, the vapor pressure decreases. When the vapor pressure equals the atmospheric pressure, liquid enters the capillary. The temperature at which this occurs is the boiling point.
List of Materials
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Lab stand5
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Thermometer clamp5
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Digital thermometer (60 -150ºC range)5
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Glass capillary tube20
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Rubber band5
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Test tube (3 -5 mm)10
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1-mL glass pipette10
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Pipette bulb10
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Acetone (99.5%> pure)10 mL
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Ethanol (99.5% pure)10 mL
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25-mL glass beaker5
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250-mL glass beaker5
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Stirring hotplate5
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25-mL glass bottle with cap2
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Powder funnel2
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Digital barometer1
Lab Prep
Source: Lara Al Hariri at the University of Massachusetts Amherst, MA, USA
- Preparation of the Laboratory
Here, we show the laboratory preparation for 10 students working in pairs, with some excess. Please adjust quantities as needed.
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Put on the necessary personal protective equipment, including a lab coat, chemical splash goggles, and gloves.
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The students will need to use both acetone and ethanol in their experiment. Label a glass bottle with the solvent name, and then pour a smaller volume of solvent from the stock bottle into the glass bottle, ensuring that there is enough for each group to have about 1 mL. Do the same for the other solvent and then place these bottles in a communal hood.
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Set out the following glassware and equipment at each student lab station (we suggest that students work in pairs):
1 Lab stand 1 Hotplate 1 Lab jack 1 Rubber band 1 Medium 3-prong clamp 3-4 Glass capillary tubes 1 Pipette bulb 2 1-mL volumetric pipettes 2 Glass test tubes 1 250-mL beaker 1 25-mL beaker 1 Digital thermometer
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