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Physical Changes, Chemical Changes, and How to Tell the Difference

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Physical Changes, Chemical Changes, and How to Tell the Difference LIVE INTERACTIVE LEARNING @ YOUR DESKTOP Physical Changes, Chemical Changes, and How to Tell the Difference Presented by: Adam Boyd December 5, 2012 6:30 p.m. – 8:00 p.m. Eastern time 1 Introducing today’s presenter… Adam Boyd Senior Education Associate Office of K–8 Science American Chemical Society 2 American Chemical Society Physical Changes, Chemical Changes, and How to Tell the Difference Adam M. Boyd Education Division American Chemical Society Our Goals Inquiry Based Activities – Clues of chemical change How to Science Background distinguish? – Chemical and Physical Properties – Chemical and Physical Change American Chemical Society 4 IYC Kits www.acs.org/iyckit American Chemical Society 5 IYC Kit Lesson Components 1. Lesson Summary 1 2. Key Concepts 3. Safety 2 4. The chemistry continues 5. Scientist introduction 6. Teacher demonstration(s) 3 7. Student activity Student activity sheet 8. Class discussion 9. Teacher demonstration 10. Application 4 American Chemical Society 6 IYC Kit Classic clues of chemical change? American Chemical Society 7 IYC Kit 1. Production of a gas Classic clues of chemical change? American Chemical Society 8 IYC Kit 1. Production of a gas Classic clues of chemical change? 2. Color change American Chemical Society 9 IYC Kit 1. Production of a gas Classic clues of chemical change? 2. Color change 3. Formation of a precipitate American Chemical Society 10 IYC Kit 1. Production of a gas Classic clues of chemical change? 2. Color change 3. Formation of a precipitate 4. Temperature change American Chemical Society 11 Chemical change or Physical change? Chemical change or Physical change? Chemical Change Physical Change IYC Kit 1. Production of a gas 2. Color change 3. Formation of a precipitate 4. Temperature change 1 3 2 4 American Chemical Society 14 Production of a Gas 1. Teacher demo – Citric acid + sodium bicarbonate – Ask students: was this a chemical change? 2. Investigation – “Foam dome” – Mix citric acid solution with sodium bicarbonate and liquid detergent – Controlling products of a chemical reaction 3. Extension: Air Bags American Chemical Society 15 Production of a Gas 1. The production of a gas is one clue that a chemical change may have taken place 2. You can control the amount of products formed by controlling the amount of reactants American Chemical Society 16 IYC Kit 1. Production of a gas 2. Color change 3. Formation of a precipitate 4. Temperature change 1 3 2 4 American Chemical Society 17 Color Change 1. Teacher demo – Carbon dioxide with a bromothymol blue indicator solution – Ask students: was this a chemical change? 2. Investigation – Can you produce each color within universal indicator’s range by adding citric acid and sodium bicarbonate dropwise? 3. Extension: Diabetes monitoring American Chemical Society 18 Color Change 1. A color change is one clue that a chemical change may have taken place 2. Adding a base to an acidic solution makes the solution less acidic. 3. Adding an acid to a basic solution makes the solution less basic. 4. Carbon dioxide gas reacts with water to form carbonic acid. American Chemical Society 19 IYC Kit 1. Production of a gas 2. Color change 3. Formation of a precipitate 4. Temperature change 1 3 2 4 American Chemical Society 20 Formation of a Precipitate 1. Teacher demo – Calcium chloride + sodium carbonate – Ask students: was this a chemical change? 2. Investigation – Filter precipitate formed by mixture of calcium chloride and sodium bicarbonate 3. Extension: Water Purification American Chemical Society 21 Formation of a Precipitate 1. The formation of a precipitate is one clue that a chemical change may have taken place 2. A precipitate is a solid that forms in the chemical reaction between liquids. It does not dissolve in the resulting solution. American Chemical Society 22 IYC Kit 1. Production of a gas 2. Color change 3. Formation of a precipitate 4. Temperature change 1 3 2 4 American Chemical Society 23 Temperature Change 1. Teacher demo – Foot warmer made of iron filings – Ask students: was this a chemical change? 2. Student Activity – Citric acid + sodium bicarbonate (Endothermic) – Sodium bicarbonate + calcium chloride (Exothermic) 3. Investigation – Adjust reactants to get temperature between 40° and 50° C. 4. Extension: Meals-Ready-to-Eat (MREs) American Chemical Society 24 Temperature Change 1. A temperature change is one clue that a chemical change may have taken place 2. When the temperature increases during a chemical reaction, it is called an exothermic reaction. 3. When the temperature decreases during a chemical reaction, it is called an endothermic reaction. American Chemical Society 25 Questions? American Chemical Society 26 Our Goals Inquiry Based Activities – Clues of chemical change Science Background – Chemical and Physical Properties – Chemical and Physical Change American Chemical Society 27 Toss Up: Chemical or Physical? • Adding Kool-Aid mix to water • Smoke emanates from dry ice at room temperature • Mentos are dropped into a 2-liter of Diet Coke American Chemical Society 28 So how do we really know? Let’s take a moment to review some chemistry fundamentals – Chemical and Physical Properties – Chemical and Physical Change American Chemical Society 29 Chemical Properties • Exhibited by matter as it undergoes changes in composition • Related to the kinds of chemical changes that substances undergo Examples – Photosynthesis • In the presence of sunlight and chlorophyll, carbon dioxide reacts with water to produce glucose and oxygen – Metal Rusts • Iron reacts with oxygen and water to produce iron oxides and iron hydroxides (rust) American Chemical Society 30 Physical Properties • Can be observed in the absence of any change in composition • Some depend on conditions under which they are measured Examples: color, density, hardness, melting point, boiling point American Chemical Society 31 Chemical Change 1. One or more substances are used up (at least partially) 2. One or more new substances are formed Examples Photosynthesis 6CO2 + 6H2O C6H12O6 + 6O2 Metal Rusts 2Fe(s) + 3/2 O2(aq) + xH2O(l) Fe2O3 · xH2O(s) American Chemical Society 32 Chemical Change • The reactants are on the left side of the equation and the products are on the right. • In the reaction, the bonds in the methane and oxygen come apart, the atoms rearrange and then re-bond to form water and carbon dioxide. American Chemical Society 33 Chemical Change • All the atoms in the reactants form the products so the mass of the reactants and the products is the same. • No new atoms are created and no atoms are destroyed American Chemical Society 34 Chemical Change American Chemical Society 35 Chemical Change • 3 Carbon atoms • 5 Hydrogen atoms • 5 Oxygen atoms • 1 Sodium atom American Chemical Society 36 Chemical Change • 3 Carbon atoms • 3 Carbon atoms • 5 Hydrogen atoms • 5 Hydrogen atoms • 5 Oxygen atoms • 5 Oxygen atoms • 1 Sodium atom • 1 Sodium atom American Chemical Society 37 Physical Change • No change in chemical composition • May suggest that a chemical change has taken place Ice melts H2O (s) H2O (l) American Chemical Society 38 Questions? American Chemical Society 39 How to tell the difference? In a chemical change something new is made. Always. American Chemical Society 40 How to tell the difference? In a physical change nothing new is made. Always. American Chemical Society 41 Popcorn II: The Quickening A few closing notes • IYC kit makes clear definition of chemical change immediately • Remember to complete the evaluation to receive a free IYC kit • For more free resources: 9 middleschoolchemistry.com 9 inquiryinaction.org 9 acs.org/iyckit • Contact Us Adam Boyd | [email protected] James Kessler | [email protected] American Chemical Society 43 Thanks to today’s presenter! Adam Boyd Senior Education Associate Office of K–8 Science American Chemical Society 44 Thank you to the sponsor of today’s web seminar: This web seminar contains information about programs, products, and services offered by third parties, as well as links to third-party websites. The presence of a listing or such information does not constitute an endorsement by NSTA of a particular company or organization, or its programs, products, or services. 45 National Science Teachers Association Gerry Wheeler, Interim Executive Director Zipporah Miller, Associate Executive Director, Conferences and Programs Al Byers , Ph.D., Assistant Executive Director, e-Learning and Government Partnerships Flavio Mendez, Senior Director, NSTA Learning Center NSTA Web Seminars Brynn Slate, Manager Jeff Layman, Technical Coordinator 46.
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