Introduction: The pressure of the atmosphere affects many aspects of our lives, including such things as the weather and baking. The boiling point of a liquid is related to pressure. A liquid begins to boil when the pressure of the vapor above a liquid is equal to the pressure of the atmosphere. In this exercise you will discover how the pressure above a liquid affects the boiling point of the liquid and how the pressure of a gas affects its volume.
NOTE: This lab may be done as a demonstration.
Purpose: To determine the effect that atmospheric pressure has on boiling point and on volume.
Experiment A: Boiling water
Materials needed:
250 mL Flask
Solid rubber stopper to fit the flask Hot plate
Rubber mitts
Ziploc™ plastic bag of ice cubes
Procedure:
Fill a 250 mL flask with 50 mL of water, unstoppered Heat the flask until the water begins to boil
Turn off the heat and wait for the water to stop boiling Place the stopper securely onto the flask
Securely hold the flask with rubber mitts and invert the flask into a 250 mL beaker Place a bag of ice directly on the base of the flask.
Observation:
Questions for Expt A:
- Describe what is happening to the liquid and gas molecules when the water boils uncovered.
- Describe what the liquid or gas molecules would be doing to explain why water can boil with ice cubes on it? (Use some of these words to help you: hotter, cooler, faster, slower, smaller volume, larger volume, vacuum, pressure, temperature.)
Experiment B: Effects of pressure
Materials needed:
Empty aluminum soda pop can Hot plate
Shallow pan or dish of cool water Tongs or hot mitt
Procedure:
Fill the pan with cool water and set aside Pour about 10 mL of water into the pop can. Heat the can until the water boils and you can see vapors rising. Using hot mitts or . tongs quickly invert the pop can into the pan of water (opening submerged)
Observation:
Questions for Expt B:
- Explain how the gas molecules behaved to give the effect you observed. (Again, use some of these words to help you: hotter, cooler, faster, slower, smaller volume, larger volume, vacuum, pressure, temperature)
Post Activity Discussion (Conclusion):
What was the ‘Take Away Message’ from this lab?
What skills did you acquire?
What parts of the lab were not clear or were confusing?
