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Lesson 1.8: Launch Lesson – Introduction to Properties of Gases Unit 1: Structure and Properties...

Lesson 1.8: Launch Lesson – Introduction to Properties of Gases Unit 1: Structure and Properties of Matter Cupping – Harmless Fad or Sound Science? HANDOUT 1.8.A CUPPING: HARMLESS FAD OR SOUND MY NOTES SCIENCE? This passage is adapted from Brian Rohrig, “Cupping: Harmless Fad or Sound Science?” ©2018 by American Chemical Society. PCN Photography / Alamy Stock Photo 1 If you watched Michael Phelps swim at the 2016 Summer Olympics in Rio de Janeiro, you might have noticed more than his lightning-fast speed as he added five gold medals to his already impressive collection. You may have wondered why his back and shoulders were covered with circular purple welts. These welts were the result of cupping therapy, an ancient medical practice that involves attaching cups to the skin in an effort to improve blood flow and boost performance. 2 Other athletes and Hollywood stars have also taken up this practice. This star power has given cupping a major reputation boost. Some people are trying this alternative therapy to gain relief for everything from migraines to back pain. Others feel it relaxes them. But is cupping effective? Or are the perceived benefits the result of the placebo Student Resource 51 Pre-AP Chemistry © 2021 College Board CHEM_U1_SR.indd 51 10/04/20 9:58 PM  Lesson 1.8: Launch Lesson – Introduction to Properties of Gases Unit 1: Structure and Properties of Matter HANDOUT effect—your mind convincing your body that a 1.8.A treatment is working? Before we address these questions, let’s take a look at the mechanics of MY NOTES cupping. What Is Cupping? The air is heated in cups to make the The cups are placed on the client’s gas particles move faster. Some air skin, and the air inside the cups escapes from the cup. starts to cool. 3 Cupping has been around for a long time. It likely originated in China, and dates back to at least 1500 BCE. The procedure for cupping is remarkably simple. First, some air is evacuated from a bulb-like or dome-shaped cup to create a region of reduced pressure. The earliest methods for getting air out of the cup involved inserting a lit stick into a clay or bamboo cup to heat the air before placing the cup on the skin. This technique, known as fire cupping, is still practiced today. Practitioners set an alcohol-soaked cotton ball on fire, insert it in a glass cup and then take it out. The cup then goes on the skin. If not done properly, fire cupping can lead to severe burns to the skin, so it should only be practiced by a licensed professional. Pre-AP Chemistry 52 Student Resource © 2021 College Board CHEM_U1_SR.indd 52 10/04/20 9:58 PM  Lesson 1.8: Launch Lesson – Introduction to Properties of Gases Unit 1: Structure and Properties of Matter 4 A dozen or more cups may be placed on the skin at HANDOUT 1.8.A one time. Cup sizes vary from about 60 milliliters (mL) to 125 mL, with the smaller cups used on MY NOTES bony parts of the body and the larger cups for soft, fleshy areas. Practitioners claim the therapy works by boosting blood flow to the cupped sections of the body. There’s little evidence to support this claim, however. And some medical professionals note that the practice can cause blood vessels to break and clot, which impedes blood flow. What Science Can Tell Us 5 When a flame is inserted in a cup before it is placed on the skin, the particles of air—mostly N2 and O2—begin to move faster. As these particles move faster, they move farther apart. All gases spread out as they are heated, provided there is room for them to expand. In cupping, air escapes from the cup. 6 Even though heating the cup creates a mass exodus of air particles, the pressure within the cup stays constant as long as it stays hot—a few air particles moving quickly can exert just as much pressure as a lot of air particles moving slowly. Gas pressure within a container is due to particles colliding against the walls of the container and each other. 7 When the flame is removed from the cup, the air in the cup immediately begins to cool. The cup is then placed tightly against the skin. Although this doesn’t create a perfect seal, not much outside air can get in. As the air in the cup cools, the particles slow down and collide less frequently with the walls of the cup and each other. The pressure in the cup therefore drops. Student Resource 53 Pre-AP Chemistry © 2021 College Board CHEM_U1_SR.indd 53 10/04/20 9:58 PM  Lesson 1.8: Launch Lesson – Introduction to Properties of Gases Unit 1: Structure and Properties of Matter HANDOUT 8 The behavior of a gas when its temperature 1.8.A changes depends on the properties of the container that houses the gas. If the container MY NOTES is rigid and cannot expand, a change in the temperature of the gas in that container will lead to a change in pressure, since the volume must stay constant. If the container’s size can change, then the gas will expand as the temperature increases or contract as the temperature decreases, and the pressure will remain constant. 9 The cups used for cupping are rigid, so they don’t collapse when the air in the cup cools, and the interior air pressure drops. At this point, the pressure in the cup quickly becomes much lower than the outside air pressure. The cup is pressed tightly against the skin, and the skin rises in the cup. Cupping Without the Threat of Burns 10 Rather than using heat to create the cupping effect, more modern methods of the ancient therapy involve hooking the cup to a vacuum pump to remove the air. This works by creating an area of low pressure inside the pump. Air from the cup, where the pressure is higher, rushes into the pump, and the skin bulges in the cup. Pre-AP Chemistry 54 Student Resource © 2021 College Board CHEM_U1_SR.indd 54 10/04/20 9:58 PM  Lesson 1.8: Launch Lesson – Introduction to Properties of Gases Unit 1: Structure and Properties of Matter There’s No Such Thing as Suction HANDOUT 1.8.B CHALLENGE Can you make a hard-boiled egg fit inside a bottle Safety Note without damaging the egg? Follow all safety guidelines provided by your teacher. MATERIALS ƒ ƒ glass bottle with wide mouth (500 mL Erlenmeyer flask, glass milk bottle) ƒ ƒ hard-boiled egg(s), peeled ƒ ƒ matches or a lighter ƒ ƒ strips of paper PROCEDURE 1. Make sure the glass bottle is clean and dry. 2. Using a match or a lighter, light one end of the strip of paper and place it in the bottle, flame side down. 3. Place the hard-boiled egg in the mouth of the bottle and watch! ANALYSIS Based on your reading about cupping from the previous handout and your observations of the egg in the bottle, draw three particle diagrams that could be used to explain what happened. Particle Diagram 1: Air in the bottle and outside the bottle before the lit paper is placed in the bottle. Student Resource 55 Pre-AP Chemistry © 2021 College Board CHEM_U1_SR.indd 55 10/04/20 9:58 PM  Lesson 1.8: Launch Lesson – Introduction to Properties of Gases Unit 1: Structure and Properties of Matter HANDOUT Particle Diagram 2: Air in the bottle and outside the bottle after the lit paper is placed 1.8.B in the bottle. Particle Diagram 3: Air in the bottle and outside the bottle after the egg is in the bottle. Pre-AP Chemistry 56 Student Resource © 2021 College Board CHEM_U1_SR.indd 56 10/04/20 9:58 PM