Discovering the Gas Laws - Fun to Teach Science and Math

Discovering the Gas Laws - Fun to Teach Science and Math Discovering the Gas Laws The Gas Laws show the relationships between the pressure, volume, temperature and amount (moles) of gas. These are the variables in the gas law equations. The independent variable – the variable you are manipulating –is given in the explanation. You must determine which of the other variables is the dependent variable (the variable you are measuring) and determine its relationship to the independent variable. You will also determine which gas law is being demonstrated: Boyle’s Law, Charles’ Law, Gay-Lussac’s Law or Avogadro’s Law. Experiment #1 – Compressed Air (Demo) The teacher will need: a can of compressed air and a volunteer Describe what happens in the demonstration: Explanation: When the nozzle is pressed, air is released, causing the pressure of the air inside the can to decrease. This caused the ___________________ of the can to (increase / decrease). Gas Law Demonstrated (Name and Equation): _________________________________________________________ Are the variables Inversely Proportional or Directly Proportional? ________________________________________ The graph would look like this: Experiment #2 – The Water Bottle You need: 1 empty water bottle 1. Give a tightly sealed, empty, room temperature water bottle to your teacher to put into the freezer for about one minute. You are responsible for reminding her to get it out of the freezer! Record your observations. 2. Open the lid of the water bottle. Record your observations. Explanation: As the temperature decreased, the ___________________ of the bottle (increased / decreased). Gas Law Demonstrated (Name and Equation): _________________________________________________________ Are the variables Inversely Proportional or Directly Proportional? ________________________________________ The graph would look like this: Discovering the Gas Laws Page 1 of 6 Experiment #3 – The Marshmallow You need: 1 small marshmallow and 1 syringe 1. Push the plunger all the way down. Place the thumb of one hand tightly over the opening. Pull the plunger, then release it. Record your observations. 2. Remove the plunger and place a small marshmallow inside the syringe. Push the plunger so that it touches the marshmallow, then repeat the rest of step #1. Record your observations. Explanation: In step #1, you are nearly creating a vacuum. A perfect vacuum is when there are no gas particles and therefore the gas pressure is zero. As the pressure inside the syringe decreased, the ___________________ of the air inside the marshmallow (increased / decreased). Gas Law Demonstrated (Name and Equation): _________________________________________________________ Are the variables Inversely Proportional or Directly Proportional? ________________________________________ The graph would look like this: Experiment #4 – The Balloon You need: 1 balloon 1. Blow up a balloon and tie the end. Record your observations. Explanation: As the moles of gas increased, the ___________________ of the balloon (increased / decreased). Gas Law Demonstrated (Name and Equation): _________________________________________________________ Are the variables Inversely Proportional or Directly Proportional? ________________________________________ The graph would look like this: Discovering the Gas Laws Page 2 of 6 2. Squeeze one end of the balloon. (Try not to pop it!) Record your observations. Explanation: As the pressure increased, the ___________________ of the balloon (increased / decreased). (Only think about the side of the balloon you are squeezing!) Gas Law Demonstrated (Name and Equation): _________________________________________________________ Are the variables Inversely Proportional or Directly Proportional? ________________________________________ The graph would look like this: Experiment #5 – The Aluminum Can You need: one empty aluminum soda can *This should not be done without teacher supervision!* 1. Pour 15 mL of water into an empty aluminum can. 2. Place the can on a hot plate (setting: high). Heat until steam starts to rise from the can (about 1 minute). 3. Using a pair of tongs, grasp the can, invert it, and dip it into a 1 liter beaker of cool water. 4. Record your observations. Explanation: The steam forced the air out of the can. Cooling the can condensed the water vapor, leaving the can empty, and creating a near vacuum. The pressure inside the can (increased / decreased). The higher pressure outside the can caused the ___________________ of the can to (increase / decrease). Gas Law Demonstrated (Name and Equation): _________________________________________________________ Are the variables Inversely Proportional or Directly Proportional? ________________________________________ The graph would look like this: Discovering the Gas Laws Page 3 of 6 Experiment #6 – Popcorn You need: 6 kernels of popcorn and a 250 mL Erlenmeyer flask 1. Place the popcorn kernels into the Erlenmeyer flask. 2. Carefully place the flask onto a hotplate (setting: 5 to high). 3. Watch what happens (this will take 3-5 minutes). Record your observations. 4. Carefully remove the Erlenmeyer flask from the hotplate with hot-hands and throw the popcorn into the trash. Explanation: Popcorn kernels have water inside. Remember that as water is heated, it eventually boils and turns into a gas. The volume of the kernel is constant. So as the temperature increased, the ___________________ of the water vapor (increased / decreased), causing the kernel to burst open. Gas Law Demonstrated (Name and Equation): _________________________________________________________ Are the variables Inversely Proportional or Directly Proportional? ________________________________________ The graph would look like this: Summary: Temperature and volume are (directly / inversely) related because as the temperature increases, the volume (increases / decreases). Pressure and volume are (directly / inversely) related because as the pressure increases, the volume (increases / decreases). Moles of gas and volume are (directly / inversely) related because as the moles of gas increase, the volume (increases / decreases). Pressure and temperature are (directly / inversely) related because as the pressure increases, the temperature (increases / decreases). Discovering the Gas Laws Page 4 of 6 Gas Laws in the Real World Determine which gas law is being observed: Boyle’s Law, Charles’ Law, Gay-Lussac’s Law, Avogadro’s Law or Henry’s Law. Note: Henry’s Law relates the concentration (an amount, related to moles) of a gas to the partial pressure of the gas. 1. You blow up a balloon. 2. You put your balloon in the freezer and it shrinks. 3. You squeeze your balloon. 4. You lie down on an inflatable mattress. 5. Bread dough rises because yeast produces carbon dioxide. When placed in the oven, the bread rises even further. 6. A bottle of soda is opened and you hear a hissing sound. 7. The attic of a house will be hotter in the summer than the rest of the home. This occurs because hot air is less dense than cold air; therefore hot air rises. 8. A flat tire is filled with air. 9. The air pressure inside a tire is higher on a hot summer day. 10. It is a good idea to open the windows in your house slightly if a tornado is coming because the external air pressure will drop dramatically and your house could possibly “explode.” 11. A marshmallow will expand in a vacuum. 12. Popcorn pops as the temperature is increased. 13. A can of whipped cream, which contains air, should never be exposed to high temperatures – the can could explode. 14. The ear drum is a flexible membrane separating the ear canal and the middle ear. The middle ear contains air. Normally the air pressures in the ear canal and in the middle ear are equal. Riding in an elevator to the top floor in a very high building or ascending or descending in an airplane can cause your ear to “pop.” 15. How you inhale: the diaphragm moves downward, increasing the volume of the lungs. This causes the pressure inside the lungs to be less than the outside pressure so air rushes in. 16. When performing the Heimlich maneuver, you rapidly decrease the volume of the chest which causes an increase of pressure inside the lungs, which can expel an obstruction out of the windpipe. Discovering the Gas Laws Page 5 of 6 17. If you ever go scuba diving, don’t hold your breath! At low depths the pressure increases, which could cause your lungs to compress. 18. If diving at depths of greater than 60 feet, beware of “nitrogen narcosis.” This is caused by an increased concentration of nitrogen in the blood and results in a feeling of euphoria that has caused some divers to remove their respirators and other equipment. (This is why deep-sea divers often use a helium-oxygen mix rather than a nitrogen-oxygen mix.) 19. When scuba diving, you cannot return to the surface rapidly or you may get the “bends.” This occurs when nitrogen gas comes out of the blood as the pressure decreases and forms bubbles, blocking the passage of blood into the capillaries. 20. A water bottle half filled with water is sealed and placed in the refrigerator. Several hours later you take it out and notice that the sides of the water bottle are slightly caved in. 21. How an airbag works: a. Under specific conditions (a car crash), a pellet of sodium azide is ignited, producing nitrogen gas. The production of the hot nitrogen gas causes the airbag to inflate. b. However, at this point, hitting the airbag would be like hitting a brick wall. Fortunately, as the gas expands it cools down and some of the gas is allowed to escape through vents so that by the time your body hits the airbag (about 50 milliseconds after the accident), it has deflated to a much softer cushion. 22. Nice weather and gas laws (a simplistic version): a. When the weatherman states that a high pressure system is moving in, you can probably expect clear, sunny skies. An area of high pressure is created when an air mass is cooling down. As the air cools, it contracts (the volume decreases). b. As the volume decreases, the density increases, causing the air to sink. As the air sinks, surrounding air rushes in from above. The combination of the increased number of air particles and the smaller volume of the sinking air causes the air pressure to increase. (volume and pressure) Extra Information: Also as the air sinks, the air warms up. This prevents condensation, and therefore prevents cloud formation. 23. Stormy weather and gas laws (a simplistic version): a. An area of low pressure is created when an air mass is warming. As the air warms, the air expands (the volume increases). Extra Information: As the volume of air increases, the density decreases, allowing the air to rise. The warming air mass pushes air above it out of the way. The combination of the decreased number of air particles and the larger volume cause the air pressure to decrease. However, as the air moves higher into the troposphere (the part of the atmosphere from the surface of the Earth to about 7 miles above the Earth’s surface), the air cools. This allows water vapor to condense, forming clouds. Often, low pressure systems bring cloudy and rainy weather. The wind is caused by air moving from areas of high pressure to areas of low pressure. Discovering the Gas Laws Page 6 of 6