KITCHEN CHEMISTRY Chemical reaction with vinegar and baking soda

Transcription

1 KITCHEN CHEMISTRY Chemical reaction with vinegar and baking soda By Darby Sloss and Marianne Smith Edited by Anne Starace Abstract Chemistry is an important part of our lives. Kitchen Chemistry uses some common household items to introduce a few basic chemical concepts. This module demonstrates a chemical reaction. Keywords Chemical, molecule, compound, element, chemistry, chemical reaction & physical change 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. LEVEL, TIME REQUIRED AND NUMBER OF PARTICIPANTS 4 III. SAFTEY 4 IV. LIST OF MATERIALS 5 V. INTRODUCTION 5 VI. PROCEDURE 6 VII. FREQUENTLY ASKED QUESTIONS 7 VIII. TROUBLESHOOTING 8 IX. HANDOUT MASTERS 8 X. REFERENCES 8 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: -learn the difference between chemical reactions and physical changes. -observe an example of a chemical reaction. II. Level, Time Required and Number of Participants Level: This activity is intended for grades 4-8. Time Required: There is no special preparation for this activity. This activity requires 5 to 10 minutes. Number of Participants This activity is best done in small groups of 3-6. III. Safety Never allow anyone to taste the chemicals used in this module. (Vinegar and baking soda are used in food, but eating them during this activity is not sanitary.) If a chemical comes in contact with skin, thoroughly wash skin with soap and water. If a chemical comes in contact with eyes, thoroughly flush one s eyes with running water. See a doctor as soon as possible. If a chemical is spilled on the floor, it should be wiped up using a dry towel and then washed with soap and water. 4

5 IV. List of Materials Baking soda Vinegar Erlenmeyer Flask (see picture below) Crystallization dish or other device to keep the table clean (see picture below) Spatula or spoon Balloon Erlenmeyer Flask crystallization dish 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 activity. 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 6

7 Chemical reactions vs. physical changes A chemical reaction requires the breaking and/or formation of chemical bonds. If bonds are not broken or formed, a chemical reaction has NOT occurred. For example, boiling water causes water to change from the liquid phase to the gas phase (steam). Both liquid water and gaseous water (steam) are H 2 O, thus, boiling water is not a chemical reaction, it is a physical change. On the other hand, when baking soda (sodium bicarbonate) and vinegar (acetic acid) are mixed, a chemical reaction does occur. Chemical bonds are broken and formed. Many chemical reactions result in changes that can be easily visualized, as with the reaction of baking soda and vinegar. Acetic Acid Sodium Bicarbonate Carbon Dioxide Sodium Acetate water (CH 3 COOH) (NaHCO 3 ) (CO 2 ) (CH 3 COONa) (H 2 O) Note that the O-H, O-C, and O-Na bonds were broken and the O-H, O-Na, and C=O bonds were formed. One line between two elements (eg O-Na) represents a single bond (one electron being shared) and two lines between two elements (eg C=O) represents a double bond (two electrons being shared). IV. Procedure Vinegar-Baking Soda Reaction 1. Add approximately 2 teaspoons of baking soda to the Erlenmeyer flask. 2. Place the flask in the crystallization dish so that the reaction does not overflow onto the table. 3. Add several milliliters (10-20 ml) of to the flask all at once. 4. The reaction will create fizz (carbon dioxide) and a clear liquid (sodium acetate dissolved in water) as shown above. Variation 1. Put 2 teaspoons of baking soda in a deflated balloon. 2. Fill the flask, in the crystallization dish, with ml of vinegar. 3. Put the balloon around the flask without allowing the baking soda to go into the flask. 4. Tip the balloon so the baking soda falls into the flask. (see figure on following page) Hold onto the balloon so it does not separate from flask. Watch the balloon inflate. The carbon dioxide is a gas. Gases expand and take up more room than solids or liquids. The expanding CO 2 is what inflates the balloon. The observation of a gas without an external change in temperature or pressure indicates that a chemical reaction has occurred. 7

8 Cleanup The products of the vinegar - baking soda reaction can be disposed of down the drain. Rinse all dirty glassware with water. Throw away the balloon. VI. Frequently Asked Questions Q A Q A Isn t this chemical in something else? The chemicals used in this activity are used for many things. Acetic acid (vinegar) is used for cooking and cleaning. Sodium bicarbonate (baking soda) is used in many baked goods like cookies and cakes. Carbon dioxide is in the air. Sodium acetate is used in reusable hand-warmers. Can I touch or taste that? No one should intentionally touch or taste any of the liquids, solids or gases in this activity. VII. Troubleshooting There is no fizzing The vinegar or baking soda (more likely the baking soda than the vinegar) you are using has reacted and become some other compound; it has gone bad. Try a newer box of baking soda and bottle of vinegar. 8

9 The balloon does not inflate Either there is a hole in the balloon, the balloon is not fit tightly enough around the mouth of the flask, not enough vinegar and baking soda were used, or, if there is no fizzing, the vinegar and baking soda may have gone bad. VIII. Handout Masters IX. References For general chemistry information: Chemistry by Steven S. Zumdahl For more activities showing chemical reactions: The Magic School Bus Baked in a Cake For a variation of this demonstrations see the Kitchen Chemistry Script 9