Exploring Atmospheric Pressure by Making a Barometer

This activity is designed to provide students with an opportunity to create their own scientific instrument, comprehend what atmospheric pressure is, discover the relationship between pressure and boiling points and predict how one affects the other. They will need good research habits and critical thinking skills in order to discover this relationship. They will also learn how to calibrate their own instrumentation. Students will learn the affects of atmospheric pressure on matter and reactions, what causes atmospheric pressure, and how to use and read a barometer. They will learn new words such as; barometer, atmospheric pressure, and boiling point.

This activity can be used for grades 9-12 in any science classroom, but is most appropriate for a chemistry course. It is designed as lab that can be performed either inside or outside the classroom on many levels. For example, the lab could be introduced in ten minuets and the students allowed to complete the rest on their own time. Or complete classroom time could be given where it is introduced; the students build their barometers and calibrate them during class time. Students should already know how to safely boil water and how to use a thermometer to record temperature. Internet access will also be needed to some extent. This activity would fit before a unit on gas laws, a discussion of standards (STP), before phase changes, how to conduct an experiment including recording all relevant information. It would be easy to adapt to other curriculum or age/ ability levels.

To begin this activity you will need a Bunsen burner or a hot plate, a beaker of water and a thermometer. Begin heating the water and inform the students that you are going to bring the water to a boil. Ask them to record in their notebooks their prediction as to which point the water will begin to boil. Listen to a few guesses while the water is heating up, the first part of this activity is creating a discrepant event so build things up and have some fun with. Once the water has reached a full boil inform the students of its final temperature. Chances are it won't be at exactly 100 degrees Celsius (check this in the morning or your event will not be discrepant!). How is this possible? Weren't we told the boiling temperature of water is 100 degrees Celsius? Use distilled water so you can assure them there is nothing in the water. From here you will begin your lesson on atmospheric pressure and it depends on where you are in your year what angle you take. What happens when water boils would be a good question leading to phase changes. Once you've discussed why this concept is important and perhaps some background information and where the topic is going you can pass out the worksheet on atmospheric pressure and how to make your own barometer. Students are to make their own barometers at home by following the instructions give. Than, using the Internet site provided they would record on their barometer different pressure readings throughout the unit. On days when the pressure is recorded they will also boil a measured amount of water and record in their lab books a table of pressure versus boiling points. Once you decide the activity has gone long enough ask the students to make a graph of temperature versus pressure and describe in one to two sentences the relationship between pressure and boiling point. Their lab grade should include a calibrated barometer as well as the graph and sentence. Lab Handout (Microsoft Word 46kB Sep18 08)

When discussing high altitude conditions, many texts describe the air as thin. I personally dislike this description and prefer less dense or lower pressure. If you use the analogy of a column of air going into space pushing down to describe air pressure it might help students see that the air is less dense because there is less air pushing down on it forcing it closer. One concern with the barometers is the possibility of cheating. They may go through all the work of building one and never record their own data. That would defeat most of the activity's purpose. I would suggest either keeping the barometers in the room, or testing their calibrating skills by checking all of them for accuracy. It would only take lining them up and comparing them to a known barometer to see who copied lines and who actually calibrated their own. This is part of what makes this activity great or different is the ownership the students can build with their scientific tool.

The students' lab will be graded either in a lab book or a lab report depending on the standards for the class. They should have taken data, organized and drawn a conclusion from it. Also a working scientific tool, the barometer, will need to be tested.