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Investigating the Power of Air Pressure Mark as Favorite (0 Favorites)

LAB in Pressure, Dimensional Analysis, SI Units, Kitchen Chemistry. Last updated June 04, 2024.

Summary

In this lab, students will investigate air pressure through several short experiments. They will become more familiar with the concept of air pressure and its corresponding units of measurement. Students will be challenged to interpret their observations through modeling particle diagrams.

Grade Level

High School

NGSS Alignment

This lab will help prepare your students to meet the performance expectations in the following standards:

  • Scientific and Engineering Practices:
    • Using Mathematics and Computational Thinking
    • Developing and Using Models
    • Engaging in Argument from Evidence

Objectives

By the end of this lab, students should be able to

  • Recognize that the gases in air exert pressure on their surroundings.
  • Develop a simple particle diagram to help explain the behavior of gas particles.
  • Identify units for measuring pressure and convert from one unit to another.

Chemistry Topics

This lab supports students’ understanding of

  • Gases
  • Pressure
  • Measurement
  • Dimensional Analysis

Time

Teacher Preparation: 60 minutes
Lesson: 45 minutes

Materials

  • Water
  • Plastic Cup
  • Playing card/laminated index card that is large enough to cover the top of the cup
  • 12-16 oz Plastic bottle with lid (soda bottle, disposable water bottle, etc.)
  • Hammer and nail

Safety

  • Always wear safety goggles when handling chemicals in the lab.
  • Students should wash their hands thoroughly before leaving the lab.
  • When students complete the lab, instruct them how to clean up their materials and dispose of any chemicals.

Teacher Notes

  • This lab was originally designed as a demonstration for elementary and middle school teachers to use in their classrooms as The Power of Air Pressure. This lab is a modification, inspired by that resource, for use in the high school classroom.
  • For students of almost any age, the concept that the air around them exerts a force, is typically quite counterintuitive. This lab serves as an opportunity for students to make some observations as they explore air pressure.
  • Prior to this lab, students should have the understanding that particles of a gas are very far apart compared to the particles in liquids and solids. They should also know that according to the ideal gas law, the particles in a gas are in constant motion and feel very little attraction to other gas particles.
  • It’s helpful to have students think about the concept of gas pressure in terms of “collisions”. The more collisions that are happen between the particles in a sample of gas, the higher the pressure will be.
  • Additional background:
    • Pressure is measured in Force per unit Area or P = F/A.
    • The force in the case of air pressure is the weight of a column of earth’s atmosphere above the point where it is being measured.
    • At sea level, the weight of a 1 square inch column of air is about 14.7 pounds.
    • This means that the pressure at the earth’s surface (at sea level) exerted by the air (air pressure) is 14.7 pounds per square inch.
    • The very unintuitive aspect of pressure in a fluid (gas or liquid) is that the pressure measured at a point in the fluid is exerted equally in all directions – up, down, sideways, and at every angle. This means that the air exerts a pressure in all directions of about 14.7 pounds per square inch.
    • We don’t normally feel this pressure because it is all around us. It’s like a fish not feeling the water pressure all around them.
  • The experiments should all be completed over a sink for easier clean-up.
  • Prior to the lab, the teacher should puncture each bottle to make a small hole about 2 inches above the bottom using the hammer and nail.
  • Students are asked to draw models to support their explanations in the analysis section of this lab. It may be helpful to practice drawing a model together in advance of the lab to show how the gas particles in the air exert pressure on objects around them. Consider using an airplane at different altitudes as an example.
  • An Answer Key Document has been provided for teacher reference.

For the Student

Background

Air pressure, or atmospheric pressure, is the force applied to a certain area due to the amount of air present above that area. Pressure is measured in Force per unit Area or P = F/A. The force in the case of air pressure is the weight of a column of earth’s atmosphere above the point where it is being measured.

Air pressure can be expressed using units such as millimeters of mercury (mmHg), standard atmospheres (atm), pounds per square inch (psi), or kilopascals (kPa).

At sea level, the weight of a 1 square inch column of air is about 14.7 pounds. This means that the pressure at sea level exerted by the air is 14.7 pounds per square inch (psi), which is the same as 760 mmHg, 1atm, and 101.35kPa.

Conversion factors for units of pressure:
14.7 psi = 760 mmHg = 1 atm = 101.35 kPa

The very unintuitive aspect of pressure in a fluid (gas or liquid) is that the pressure measured at a point in the fluid is exerted equally in all directions—up, down, sideways, and at every angle. This means that the air exerts a pressure in all directions of about 14.7 pounds per square inch. We don’t normally feel this pressure because it is all around us. It’s like a fish not feeling the water pressure all around them. Air pressure is created by interactions between gas particles and the materials they interact with. The more particles there are, the more particle collisions there can be, and the greater the air pressure.

Prelab Questions

  1. Circle the measurement that is larger in the pairs listed below:
    1. 16.5 psi or 1.35 atm
    2. 800 mmHg or 110 kPa
    3. 99.85 kPa or 1.2 atm
    4. 13.5 psi or 740 mmHg
  2. Use dimensional analysis to solve the following questions (show your work):
    1. A student uses a pressure gauge to determine the pressure in their bike tire. It says 12.75psi, but the student needs to know the measurement in kPa. Determine the pressure value in kPa.
    2. A storm is forecasted to hit your city. The air pressure is predicted to drop to 735 mmHg. Calculate this pressure value in standard atmospheric units.

Objective

During this lab, you will observe two phenomena and generate explanations using particle models to explain what is happening using air pressure and the behavior of gases.

Materials

  • Water
  • Plastic Cup
  • Laminated index card (large enough to cover the top of the cup)
  • Plastic bottle with lid (has a puncture hole)

Safety

  • Always wear safety goggles when handling chemicals in the lab.
  • Wash your hands thoroughly before leaving the lab.
  • Follow the teacher’s instructions for cleanup of materials and disposal of chemicals.

Procedures: Part 1

  1. Fill a plastic cup more than halfway with water.
  2. Place a playing card or laminated index card on top of the cup. Make sure it covers the top of the cup.
  3. Hold the cup over the sink.
  4. While holding the card in place, turn the cup upside down.
  5. Now, carefully remove your hand from the card. Record your observations in the data table.
  6. Tilt the cup in different directions. Record your observations in the table.

Data: Part 1

Observations after removing the playing card
Observations when changing the cup’s orientation

Procedures: Part 2

  1. Fill a cup with water. Do NOT drink the water!
  2. Submerge a straw in the water. Place your thumb over the opening at the top.
  3. Without removing your thumb, lift the straw out of the cup. Record your observations in the data table.
  4. Now, remove your thumb. Record your observations in the data table.

Data: Part 2

Observations with thumb covering the top of the straw
Observations after removing thumb from the straw

Procedures: Part 3

  1. Using the disposable bottle, locate the puncture hole near the bottom.
  2. Place your finger over the hole and fill the bottle to the top with water. Don’t put the cap on yet.
  3. Hold the bottle over the sink.
  4. Take your finger off the hole. Then, record your observations in the data table.
  5. Next, with your finger still not covering the hole, screw the cap on the bottle. Record your observations in the data table.

Data: Part 3

Observations after removing hand from the hole
Observations after screwing the cap back on

Analysis

  1. Draw it! You have observed air pressure interacting with water in several activities. Choose one of the experiments and draw a particle diagram that models both the behavior of the particles in the air and the particles in the water to show the concept of air pressure. Though there are different particles in the air and water, all in your diagram can be represented using a circle for simplicity (please label appropriately).

Part 1

  1. Draw a diagram to explain what occurred during Step 5 when you removed your hand from the card. Summarize your diagram in 2 to 3 sentences.
  2. Were you surprised by your observations while moving the cup in different directions (step 6)? Why or why not? Draw a diagram if needed.

Part 2

  1. Draw a diagram to explain the difference between how the water in the straw behaves when your thumb covers the top versus when you remove your thumb from the straw.

Part 3

  1. Why is it important to place your finger over the hole while filling up the bottle?
  2. Draw a diagram to explain what occurs during Step 4 (finger is not covering the hole, and there is no cap on the bottle). Summarize your diagram in 2 to 3 sentences.
  3. Draw a diagram to explain what occurs during Step 5 (finger is not covering the hole, and there is a cap on the battle). Summarize your diagram in 2 to 3 sentences.