LESSON 23: Exploding Bags ESTIMATED TIME Setup: 5 minutes Procedure: 5 minutes

Transcription

1 LESSON 23: Exploding Bags ESTIMATED TIME Setup: 5 minutes Procedure: 5 minutes DESCRIPTION Combine vinegar and baking soda within a plastic bag to initiate a chemical reaction. OBJECTIVE This lesson demonstrates the formation of products from reactants during a chemical reaction. Students use two common household materials to observe how a chemical reaction produces new substances. The lesson can be extended to cover acids and bases. CONTENT TOPICS Scientific inquiry; properties of matter; chemical reactions; acids and bases; energy MATERIALS o Vinegar o Baking soda o Water o Plastic bag (zipper lock, quart size) o Toilet paper o Measuring cups o Spoons Always remember to use the appropriate safety equipment when conducting your experiment. Refer to the Safety First section in the Resource Guide on pages for more detailed information about safety in the classroom. Jump ahead to page 286 to view the Experimental Procedure. NATIONAL SCIENCE EDUCATION STANDARDS SUBJECT MATTER This lesson applies both Dimension 1: Scientific and Engineering Practices and Dimension 2: Crosscutting Concepts from A Framework for K 12 Science Education, established as a guide for the updated National Science Education Standards. In addition, this lesson covers the following Disciplinary Core Ideas from that framework: PS1.A: Structure and Properties of Matter PS1.B: Chemical Reactions ETS2.B: Influence of Engineering, Technology, and Science on Society and the Natural World (see Analysis & Conclusion) OBSERVATION & RESEARCH BACKGROUND Scientists sort matter by its physical and chemical properties. We use our senses or take measurements to identify physical properties. Some examples of physical properties are color, shape, boiling point, melting point, and density. Chemical properties can be identified by observing how a chemical reacts with other substances. Some examples of chemical properties include acidity, toxicity, and flammability. During the experiment, students can observe the different physical (and chemical) properties of the substances. When the vinegar and baking soda are combined, a change occurs. Matter often changes, and these changes can be either physical or chemical. A physical change is any change in a substance s form that does not change its chemical makeup. The chemical formula of the substance stays the same before and after the change. A chemical change or chemical reaction is a change that takes place when atoms of a substance are rearranged, and the bonds between the atoms are broken or formed. During a chemical reaction, the structure or composition of the materials changes. Chemical reactions occur around us all the time. They even take place inside of our bodies. When we breathe, we take in oxygen from the air, which combines with glucose (a sugar) in our bodies. These substances react to produce carbon dioxide and water vapor, which we exhale. You Be The LESSON Chemist 1: Activity Goofy Guides Putty page

2 LESSON 23: Exploding Bags When a chemical reaction is complete, the resulting substance(s) is/are different from the original substance(s). The substance or substances that start a chemical reaction are called reactants. The new substance(s) that are produced as a result of the reaction are called products. In this experiment, adding baking soda to vinegar starts a chemical reaction. The reaction produces sodium acetate and carbonic acid. The carbonic acid is unstable and instantly falls apart into carbon dioxide and water. The rapidly forming bubbles that appear during the reaction are carbon dioxide gas escaping from the mixture. Because the mixture is sealed within a bag, pressure created from the rapidly forming gas will cause the bag to burst. FORMULAS & EQUATIONS Vinegar is a mixture made up of very dilute acetic acid. Therefore, vinegar contains acetic acid and water. The chemical formula for acetic acid is C2H4O2. The chemical formula for pure water is H2O. CONNECT TO THE YOU BE THE CHEMIST CHALLENGE For additional background information, please review CEF s Challenge study materials online at Additional information on physical and chemical properties and changes can be found in the Classification of Matter section of CEF s Passport to Science Exploration: The Core of Chemistry. Additional information on chemical reactions can be found in the Chemical Reactions section of CEF s Passport to Science Exploration: Chemistry Connections. HYPOTHESIS uwhen baking soda and vinegar are combined in a sealed plastic bag, a chemical reaction will occur, releasing carbon dioxide gas and causing the bag to pop open. The chemical name of baking soda is sodium bicarbonate. It is commonly used in baking, hence its name. The chemical formula for baking soda is NaHCO3. When vinegar and baking soda are combined, an acid-base reaction occurs between the acetic acid and baking soda. CH3COOH + NaHCO3 g CH3COONa + H2CO3 This reaction produces sodium acetate (CH3COONa or NaCH3CO2) and carbonic acid (H2CO3). The carbonic acid is unstable and quickly decomposes into carbon dioxide gas (CO2) and water (H2O). H2CO3 g H2O + CO2 Fun Fact Dry ice easily sublimates directly into carbon dioxide gas at standard temperature and pressure. The carbon dioxide gas forms bubbles that can be seen as the reaction takes place. You Be The Chemist Activity Guide page 284

3 LESSON 23: Exploding Bags DIFFERENTIATION IN THE CLASSROOM LOWER GRADE LEVELS/BEGINNERS Conduct the experiment as described on page 286, but focus the lesson on classifying matter. Discuss physical properties in more detail and the different uses of different substances. Another option is to spend more time on the differences between physical and chemical changes. For example, show a picture of a pencil. Then show a picture of the pencil broken that s a physical change. Next, show a picture of cake batter and then a baked cake that s a chemical change! HIGHER GRADE LEVELS/ADVANCED STUDENTS DESCRIPTION Combine vinegar (an acid) and baking soda (a base) within a plastic bag to initiate a chemical reaction. OBJECTIVE This lesson demonstrates the formation of products from reactants during a chemical reaction. Students explore acids and bases and use two common household substances to observe a chemical reaction. OBSERVATION & RESEARCH To describe certain chemical compounds, chemists use the terms acid and base. You can determine whether a solution is an acid or a base by determining the concentration of hydrogen ions (H + ) in the solution. An ion is an atom or molecule that has lost or gained one or more of its outer electrons. Therefore, the total number of electrons is not equal to the total number of protons, so an ion will have either a negative or a positive electric charge. In general, a solution that contains a concentration of hydrogen ions (H + ) greater than the concentration in pure water is called an acid. Likewise, a solution containing an excess of hydroxide ions (OH - ) or an H + concentration less than that of pure water is called a base. Solutions containing an H + concentration equal to that of pure water are neutral. Acids, bases, and all types of matter can undergo different changes. A chemical change or chemical reaction is a change that takes place when atoms of a substance are rearranged, and the bonds between the atoms are broken or formed. During a chemical reaction, the structure or composition of the materials change. Chemical reactions occur around us all the time. When a chemical change is complete, the resulting substance(s) is/are different from the original substance(s). The substance or substances that start a chemical reaction are called reactants. The new substance(s) that are produced as a result of the reaction are called products. In this experiment, students work with common household vinegar and baking soda, which forms a basic solution when dissolved in water. Adding baking soda to vinegar starts a chemical reaction that produces sodium acetate and carbonic acid. The carbonic acid is unstable and instantly falls apart into carbon dioxide and water. The rapidly forming bubbles that appear during the reaction are carbon dioxide gas escaping from the mixture. Pressure created from the rapidly forming gas will cause the bag to burst. In addition, the starting temperature is higher than the ending temperature, so the reaction is considered to be endothermic. An endothermic change is a change that needs energy to be added. s CONNECT TO THE YOU BE THE CHEMIST CHALLENGE For additional background information, please review CEF s Challenge study materials online at Additional information on ions can be found in the Atomic Structure section of CEF s Passport to Science Exploration: The Core of Chemistry. Additional information on acids and bases can be found in the Acids, Bases, and ph section of CEF s Passport to Science Exploration: Chemistry Connections. Additional information on chemical reactions can be found in the Chemical Reactions section of CEF s Passport to Science Exploration: Chemistry Connections. You Be The Chemist Activity Guide page 285

4 EXPERIMENTATION LESSON 23: Exploding Bags As the students perform the experiment, challenge them to identify the independent, dependent, and controlled variables, as well as whether there is a control setup for the experiment. (Hint: If the substance added to the vinegar changes, will the reaction change?) Review the information in the Scientific Inquiry section on pages to discuss variables. DATA COLLECTION Have students record data in their science notebooks or on the following activity sheet. What is a physical change? What is a chemical change? What occurs when the vinegar and baking soda are combined? Have students answer the questions on the activity sheet (or similar ones of your own) to guide the process. EXPERIMENTAL PROCEDURE 1. Tear off two squares of toilet paper from a toilet paper roll. NOTES 2. Add a large spoonful of baking soda to the center of one of the toilet paper squares, and carefully wrap the toilet paper around it. Wrap the second toilet paper square around the first. 3. Have one student hold the plastic bag open as another student adds ¼ cup of vinegar and ¼ cup of warm water to the bag. 4. Place the wrapped baking soda in the bag, and quickly seal it. Gently swirl the liquid around so that it soaks the toilet paper. 5. Place the bag down and watch it inflate and eventually pop. (If the bag does not pop, allow the students to gently touch the bag to see if they can feel a temperature change.) Protective eyewear should be worn for this experiment. This experiment should be conducted outside or within a sink or large bowl/pan to minimize the mess. You Be The Chemist Activity Guide page 286

5 LESSON 23: Exploding Bags ANALYSIS & CONCLUSION Use the questions from the activity sheet or your own questions to discuss the experimental data. Ask students to determine whether they should accept or reject their hypotheses. Review the information in the Scientific Inquiry section on pages to discuss valid and invalid hypotheses. ASSESSMENT/GOALS Upon completion of this lesson, students should be able to Apply a scientific inquiry process and perform an experiment. Define physical and chemical properties and give examples of each. Differentiate between physical and chemical changes. Identify the reactants and products of a chemical reaction. Explain the chemical reaction that occurs during the experiment and what gas is being produced. Identify common household acids and bases (see Differentiation in the Classroom). MODIFICATIONS/EXTENSIONS Modifications and extensions provide alternative methods for performing the lesson or similar lessons. They also introduce ways to expand on the content topics presented and think beyond those topics. Use the following examples, or have a discussion to generate other ideas as a class. Ask the students what they would expect to happen if the amount of baking soda added to vinegar was increased. Try testing different amounts of baking soda, and have the students record the results. Add less baking soda to the vinegar, so the bag will inflate but not pop. Have students touch the inflated bag. Students should notice that that bag feels colder, indicating that an endothermic reaction took place. Try combining other substances to create a chemical reaction within the bag. For example, try combining lemon juice and baking soda or baking powder and vinegar to see if there is a reaction. Be sure to research the reaction of different products and read the safety precautions on product labels before combining them. Randomly mixing chemical substances is dangerous. REAL-WORLD APPLICATIONS Fun Fact The reaction between baking soda and vinegar is the reaction used to create miniature volcanoes. Baking soda and vinegar are known for their cleaning capabilities. Baking soda can be used to remove stains on pots, appliances, and clothing. It is also used as a deodorizer. Diluted vinegar is a disinfectant and deodorizer that can be used to clean various surfaces. COMMUNICATION Discuss the results as a class and review the activity sheet. Review the information in the Scientific Inquiry section on pages to discuss the importance of communication to scientific progress. You Be The Chemist Activity Guide page 287

6 OBSERVE & RESEARCH 1. Write down the materials you observe. 2. Predict how these materials may be used. 3. Define the following key terms. Then, provide an example of each by writing the example or drawing/pasting an image of the example. Term Definition Example (write or add image) Physical property Chemical property Physical change Chemical reaction Reactant Product 4. Consider the effects of combining vinegar and baking soda inside a plastic bag and why you expect such results. uwrite your hypothesis. You Be The Chemist Activity Guide page 288

7 PERFORM YOUR EXPERIMENT 1. Tear off two squares of toilet paper from a toilet paper roll. 2. Add a large spoonful of baking soda to the center of one of the toilet paper squares, and carefully wrap the toilet paper around the baking soda. Wrap the second toilet paper square around the first. 3. Have a partner hold the plastic bag open for you. Add ¼ cup of vinegar and ¼ cup of warm water to the bag. 4. Place the wrapped baking soda in the bag, and quickly seal it. Gently swirl the liquid around so that it soaks the toilet paper. 5. Place the bag down and observe. ANALYZE & CONCLUDE 1. Describe the baking soda. 2. Describe the vinegar. 3. What happens when the baking soda and vinegar interact? 4. What gas forms during the chemical reaction? Explain. 5. Is your hypothesis valid? Why or why not? If not, what would be your next steps? You Be The Chemist Activity Guides page 289

8 EXPAND YOUR KNOWLEDGE ADVANCED 1. Define the following key terms. Then, provide an example of each by writing the example or drawing/pasting an image of the example. Term Definition Example (write or add image) Acid Base Neutral 2. The following equation represents the combined chemical reaction that occurred. Label the reactants and the products. CH3COOH + NaHCO3 g CH3COONa + H2CO3 g H2O + CO2 3. Give examples of other everyday chemical reactions. You Be The Chemist Activity Guide page 290

9 ANSWER KEY: Below are suggested answers. Other answers may also be acceptable. OBSERVE & RESEARCH 1. Write down the materials you observe. Vinegar, baking soda, plastic bags, toilet paper, measuring spoons, spoons 2. Predict how these materials may be used. Vinegar and baking soda may be used in cooking or cleaning. Plastic bags may be used to hold materials. Toilet paper may be used to clean up a mess. These materials may be combined to create a chemical reaction. 3. Define the following key terms. Then, provide an example of each by writing the example or drawing/pasting an image of the example. Physical property Term Definition Example (write or add image) A property of a substance that can be experienced using the human senses and often detected through a measuring device; physical properties can be observed without reacting the substance with some other substance. Chemical property Physical change Chemical reaction A property of an object characterized by reactions that change the object s identity; describe an object s potential to undergo some chemical change or reaction due to its composition. A change that alters the form or appearance of a substance but does not change the chemical makeup of the substance or create a new substance. A change that takes place when atoms of one or more substances are rearranged, and the bonds between the atoms are broken or formed to produce new substances. Reactant A starting material for a chemical reaction. Product A substance formed as a result of a chemical reaction. 4. Consider the effects of combining vinegar and baking soda inside a plastic bag and why you expect such results. uwrite your hypothesis. When baking soda and vinegar are combined in a sealed plastic bag, a chemical reaction will occur, releasing carbon dioxide gas and causing the bag to pop open. You Be The Chemist Activity Guide page 291

10 ANSWER KEY: Below are suggested answers. Other answers may also be acceptable. PERFORM YOUR EXPERIMENT 1. Tear off two squares of toilet paper from a toilet paper roll. 2. Add a large spoonful of baking soda to the center of one of the toilet paper squares, and carefully wrap the toilet paper around the baking soda. Wrap the second toilet paper square around the first. 3. Have a partner hold the plastic bag open for you. Add ¼ cup of vinegar and ¼ cup of warm water to the bag. 4. Place the wrapped baking soda in the bag, and quickly seal it. Gently swirl the liquid around so that it soaks the toilet paper. 5. Place the bag down and observe. ANALYZE & CONCLUDE 1. Describe the baking soda. The baking soda is a white, dry powder. 2. Describe the vinegar. The vinegar is translucent. 3. What happens when the baking soda and vinegar interact? The baking soda and vinegar undergo a chemical reaction, which releases a gas that produces bubbles. These bubbles form quickly, creating a foamy mass inside the bag. 4. What gas forms during the chemical reaction? Explain. One of the initial products of the reaction breaks down further into carbon dioxide (CO2) and water. The gas bubbles seen forming inside the bag are made of CO2. 5. Is your hypothesis valid? Why or why not? If not, what would be your next steps? Answer 1: Valid because the data support my hypothesis. Answer 2: Invalid because the data do not support my hypothesis. I would reject my hypothesis and could form a new one, such as You Be The Chemist Activity Guide page 292

11 ANSWER KEY: Below are suggested answers. Other answers may also be acceptable. EXPAND YOUR KNOWLEDGE ADVANCED Have students complete this section if you used the advanced differentiation information, or challenge them to find the answers to these questions at home and discuss how these terms relate to the experiment in class the next day. 1. Define the following key terms. Then, provide an example of each by writing the example or drawing/pasting an image of the example. Term Definition Example (write or add image) Acid A solution that contains an excess of hydrogen ions (H + ); acids have a higher concentration of hydrogen ions than pure water. Base A solution that has an excess of hydroxide ions (OH - ); bases have a lower concentration of hydrogen ions than pure water. Neutral A solution that contains a concentration of hydrogen ions (H + ) that is equal to that of pure water. 2. The following equation represents the chemical reaction that occurred. Label the reactants and the products. CH3COOH + NaHCO3 g CH3COONa + H2CO3 g H2O + CO2 product reactant reactant product (then reactant) product product 3. Give examples of other everyday chemical reactions. The ingredients in toothpaste react when you brush your teeth. When you eat, the acids in your stomach break down the foods so they can be used in various processes and to generate energy. You Be The Chemist Activity Guide page 293