CHEMISTRY: Sublimation of Dry Ice

Transcription

1 CHEMISTRY: Sublimation of Dry Ice By Darby Sloss and Marianne Smith Edited by Anne Starace Abstract Chemistry is an important part of our lives. This module demonstrates sublimation. Keywords Chemical, molecule, element, dry ice, sublimation, compound, chemistry, chemical reaction, physical change, solids & gases Funded by the National Science Foundation and the University of Nebraska

2 Content Standards K History & Process Standards K Skills Used/Developed: 2

3 Table of Contents I. OBJECTIVES 4 II. SAFTEY 4 III. LEVEL, TIME REQUIRED AND NUMBER OF PARTICIPANTS 4 IV. LIST OF MATERIALS 5 V. INTRODUCTION 5 VI. PROCEDURE 6 VII. FREQUENTLY ASKED QUESTIONS 6 VIII. TROUBLESHOOTING 7 IX. HANDOUT MASTERS 7 X. REFERENCES 7 Everything in the world is made of CHEMICALS! One of the most amazing things about chemicals is the way they can join together to make different new chemicals. That s why chemicals can make up all the zillions of different things in the world! WonderScience magazine 3

4 I. Objectives: Students will: -observe changes in a balloon s volume to indicate the presence of a gas. -learn that sublimation is a physical change where a solid changes directly into a gas. -understand that dry ice is very cold and must be handled using appropriate safety procedures. II. Safety Dry ice can cause severe frostbite. Do not touch dry ice with bare skin. Be careful not to add too much dry ice to the balloon, lest it burst. Wear goggles just in case the balloon bursts. Do not let anyone stand close to the balloon if they are not wearing goggles. III. Level, Time Required and Number of Participants Level: This activity is intended for grades 4 and up, but requires close adult supervision. Younger students should not handle dry ice. Time Required: Preparation involves obtaining dry ice. This activity requires 5 to 10 minutes. Number of Participants:

5 IV. List of Materials Funnel (you must be able to wrap a balloon around the small end) Balloons Dry Ice (available at most ice cream stores) Thermos or cooler to transport dry ice Spatula, tongs, or other device to pick up dry ice Thermal gloves Goggles (one per person) funnel 5

6 V. Introduction The periodic table organizes and includes the all the known elements. For example, sodium (Na) and nitrogen (N) are elements. The smallest amount of an element is an atom. Only a few elements, called the noble gases, consist of individual atoms that move about independently of one another. In other words, the noble gases do not usually react with other elements. These elements are helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn). Notice that all of these elements are in the same column. Other elements will usually react with each other, forming molecules. A chemical reaction is the breaking or forming of chemical bonds. A molecule is a group of atoms (2 or more) joined together by chemical bonds. Molecules move as a single unit. Molecules may consist of identical atoms, as in oxygen (O 2 ), or different atoms, as in water (H 2 O). The terms molecule, compound and chemical can be used interchangeably in this module. A chemical bond is the force that holds two atoms together. For example, water is a molecule composed of one oxygen atom and two hydrogen atoms. The hydrogen atoms are bound to the oxygen. Chemists use several different notations to represent a chemical bond. The most common is a line between two atoms. The molecular structure of water using lines to represent bonds is depicted in Figure 1. O H H Figure 1 Dry Ice Dry ice is frozen carbon dioxide (CO 2 ). This is how chemists draw carbon dioxide: O=C=O Notice that two lines are drawn between each element. Two lines symbolize a double bond. A double bond is one in which two electrons are being shared. 6

7 Carbon dioxide is a gas at room temperature. When frozen carbon dioxide--which is considerably colder than room temperature-- is warmed to room temperature, it expands and turns into a gas. State changes happened all the time. For example, when you take ice cream out of the freezer, it changes states, from solid to liquid, because of the temperature change. When a chemical goes from a solid to a gas, we say it sublimes. Sublimation is not a chemical reaction-- it is a change of state, from solid to gas. Sublimation, as well as the ice cream example, are examples of a physical changes. VI. Procedure Dry Ice Inflation of a Balloon 1. Put on goggles. 2. Stretch balloon around the small end of a funnel. 3. Using gloves and the spatula, add about a teaspoon of dry ice to the balloon. 4. Remove the funnel and tie the balloon. 5. The balloon will begin to inflate. Shake the balloon to show that some of the solid remains. After several minutes the balloon will be fully inflated and no solid will remain. The dry ice inside the balloon is subliming; it is going from a solid to a gas. Gases take up more space than solids because in a gaseous state the Attachment of the balloon to the funnel for addition of dry ice. molecules are hotter and move around more than in a liquid or solid state. The gaseous CO 2 molecules bouncing around the inside of the balloon cause the balloon to inflate. (see Solids, Liquids, Gases modules for more activities and explanations of state changes) Note that you can expediate the inflation of the balloon by using the warmth of you hands to warm the balloon. Be careful. Dry ice is very cold. If the balloon pops, dry ice can touch the skin and cause immediate frost bite. Do not put more than a teaspoon of dry ice in the balloon to prevent it from bursting. VII. Frequently Asked Questions Q A What is dry ice? Dry ice is frozen carbon dioxide. Carbon dioxide is in the air all around us. Plants need carbon dioxide to survive. Q. How do you make dry ice? A. First of all you need to isolate some carbon dioxide. In the Kitchen Chemistry: chemical reaction with vinegar and baking soda module, the activity isolated gaseous carbon dioxide in a balloon. Once you have isolated carbon dioxide, you need to make it into a 7

8 solid. This can be done by compressing gaseous carbon dioxide into a liquid and then to a solid. Q. How cold is dry ice? A. Carbon dioxide freezes at about 194 degrees Kelvin; that is 79 degrees Celsius and degrees Fahrenheit! Q. What are some common uses of dry ice? A. Dry ice is used to make fog in theatrical productions, to keep food cold, to clean (dry ice blasting instead of sandblasting), to make carbonated beverages, etc. VIII. Troubleshooting The balloon doesn t inflate Check to see if there is a hole in the balloon or if it is not tied tightly enough. IX. Handout Masters See questions for students on page 9 X. References For general chemistry information: Chemistry by Steven S. Zumdahl For more information about dry ice and some more activities with dry ice: For a variation of this demonstrations see the Kitchen Chemistry Script 8

9 Questions for participants: Describe the dry ice. What do you think will happen after the dry ice has been put in the balloon? What do you see happening after the dry ice has been inside the balloon for a few moments? How could you explain what is happening? 9