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
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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
Science Background – Chemical and Physical Properties
How to distinguish?
– Chemical and Physical Change
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IYC Kits www.acs.org/iyckit
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IYC Kit Lesson Components 1
1. Lesson Summary 2. Key Concepts 3. Safety
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4. The chemistry continues 5. Scientist introduction 6. Teacher demonstration(s) 7. Student activity
Student activity sheet
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8. Class discussion 9. Teacher demonstration 10. Application 4
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IYC Kit Classic clues of chemical change?
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IYC Kit 1. Production of a gas
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Classic clues of chemical change?
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IYC Kit 1. Production of a gas
Classic clues of chemical change?
2. Color change
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IYC Kit 1. Production of a gas
Classic clues of chemical change?
2. Color change 3. Formation of a precipitate
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IYC Kit 1. Production of a gas
Classic clues of chemical change?
2. Color change 3. Formation of a precipitate 4. Temperature change
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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
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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
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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
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IYC Kit 1. Production of a gas 2. Color change 3. Formation of a precipitate 4. Temperature change
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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
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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.
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IYC Kit 1. Production of a gas 2. Color change 3. Formation of a precipitate 4. Temperature change
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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
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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.
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IYC Kit 1. Production of a gas 2. Color change 3. Formation of a precipitate 4. Temperature change
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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
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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.
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Questions?
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Our Goals Inquiry Based Activities – Clues of chemical change
Science Background – Chemical and Physical Properties – Chemical and Physical Change
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Toss Up: Chemical or Physical? •
Adding Kool-Aid mix to water
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Smoke emanates from dry ice at room temperature
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Mentos are dropped into a 2-liter of Diet Coke
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So how do we really know? Let’s take a moment to review some chemistry fundamentals – Chemical and Physical Properties – Chemical and Physical Change
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Chemical Properties •
Exhibited by matter as it undergoes changes in composition
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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)
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Physical Properties •
Can be observed in the absence of any change in composition
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Some depend on conditions under which they are measured
Examples: color, density, hardness, melting point, boiling point
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Chemical Change 1.
One or more substances are used up (at least partially)
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One or more new substances are formed
Examples Photosynthesis 6CO2 + 6H2O
C6H12O6 + 6O2
Metal Rusts 2Fe(s) + 3/2 O2(aq) + xH2O(l)
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Fe2O3 · xH2O(s)
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Chemical Change
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The reactants are on the left side of the equation and the products are on the right.
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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.
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Chemical Change
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All the atoms in the reactants form the products so the mass of the reactants and the products is the same.
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No new atoms are created and no atoms are destroyed
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Chemical Change
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Chemical Change
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3 Carbon atoms
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5 Hydrogen atoms
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5 Oxygen atoms
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1 Sodium atom
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Chemical Change
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3 Carbon atoms
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3 Carbon atoms
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5 Hydrogen atoms
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5 Hydrogen atoms
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5 Oxygen atoms
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5 Oxygen atoms
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1 Sodium atom
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1 Sodium atom
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Physical Change •
No change in chemical composition
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May suggest that a chemical change has taken place
Ice melts H2O (s)
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H2O (l)
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Questions?
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How to tell the difference?
In a chemical change something new is made. Always. American Chemical Society
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How to tell the difference?
In a physical change nothing new is made. Always. American Chemical Society
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Popcorn II: The Quickening
A few closing notes
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IYC kit makes clear definition of chemical change immediately Remember to complete the evaluation to receive a free IYC kit
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For more free resources: 9 middleschoolchemistry.com 9 inquiryinaction.org 9 acs.org/iyckit
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Contact Us Adam Boyd |
[email protected] James Kessler |
[email protected]
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Thanks to today’s presenter!
Adam Boyd Senior Education Associate Office of K–8 Science American Chemical Society
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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
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