Lecture 2: F 9/5/07 Scientific Terms, Laws and Debate (1:3-4) NAS Building in Washington, DC ?The investigation of truth is in one way hard and in another way easy. An indication of this is found in the fact that no one is able to attain the truth entirely, but everyone says something true about the nature of things, and by the union of all a considerable amount is amassed.? -Aristotle in ?Metaphysics? Review Chemistry deals with the composition, structure, and properties of substances and with the transformations that they undergo Q u e s t i o n H y p o t h e s i s D a t a / F a c t G a t h e r i n g E v a l u a t i o n Course Goals: 1) Chemical concepts 2) Problem solving through the process of scientific inquiry 3) Communication, team work, and creativity Outline 1. Scientific Terms: Fact, Law, Theory, Hypothesis, and Model 2. Matter: Theories and Laws of Substance a) Phlogisten/Conservation of Matter b) Constant Composition c) Chemical and Physical Change 3. Concept Questions 4. Debate 5. Scientific Sources Define the following: ? Fact ? Law ? Theory ? Hypothesis ? Model FACT: In science, an observation that has been repeatedly confirmed. (Consensus) LAW: A descriptive generalization about how some aspect of the natural world behaves under stated circumstances (Predictive) THEORY: In science, a well-substantiated explanation of some aspect of the natural world that can incorporate facts, laws, inferences, and tested hypotheses. (Falsifiable) Some Examples of Laws as stated by Dalton Law of Conservation of Matter ? In an ordinary chemical reaction matter is neither created nor destroyed. ? The sum of the masses of the reactants equals the sum of the masses of the products. Law of Constant Composition ? A chemical compound always contains the same elements in the same proportions by mass. Hypothesis: A testable statement about the natural world that can be used to build more complex inferences and explanations These definitions (and an excellent explanation of the scientific method) can be found at: http://www.nap.edu/readingroom/books/evolution98/ Model: A description or analogy used to help visualize something (as an atom or theory) that cannot be directly observed Iron Fe 10 g Hematite Fe2O3 14.3 g http://www.theodoregray.com/periodictabledisplay/Elem ents/026/index.s8.html www.geoclassics.com/hematite.htm ? 10 g + ___? ? 14.3 g ?? The Lomonosov-Lavoisier Law Law of Conservation of Matter ? In an ordinary chemical reaction matter is neither created nor destroyed. ? The sum of the masses of the reactants equals the sum of the masses of the products. 10 g + ___? ? 14.3 g 2 Fe + 3/2 O2 ? Fe2O3 reactants products Chemical change: rearrangement of atoms in the reacting substances to give new chemical combinations Dalton?s Law of Constant Composition ? Element: cannot be decomposed by any chemical reactions into simpler substances (cannot be separated into other kinds of matter by a physical process) ? Compound: composed of two or more elements chemically combined Law of Constant Composition A chemical compound always contains the same elements in the same proportions by mass. The ?Law of Constant Composition? (compounds composed of two or more elements in definite proportions) also has an older name given by Joseph Proust. The Law of Definite Proportions Joseph Proust 1754-1826 Claude Berthollet 1748-1822 Supported Law Opposed LawBut conceded to Proust I also discovered Bleach (NaOCl) ? Picture from: http://en.wikipedia.org/wiki/Image:Defecttypes.png Violation of the Law of Constant Composition Physical Change ? Change of phase: No change in chemical identity http://wps.prenhall.com/wps/media/objects/165/169061/GIFS/AACQJAL0.JPG Question 1 What is the mass of the solution when 1 pound of salt is dissolved in 20 pounds of water? a.19 Pounds. b.20 Pounds. c.Between 20 and 21 pounds. d.21 pounds. e.More than 21 pounds. Question 2 ? There are two identical steel beams. One is placed on each side of a balance. A flame is used to heat one of the steel beams. Does the balance move? If so, how and why? Question 3 1) As a candle burns, it gives off light and heat. When a glass rod is held in the yellow part of the flame, a black film forms on the rod. a) What is the source of the black film on the rod? b) Is there a chemical change or a physical change in the candle as it burns? c) Give an example of a chemical change: d) Give an example of a physical change Question 4 Assume a beaker of pure water has been boiling for 30 minutes. What is in the bubbles in the boiling water? a.Air. b.Oxygen gas and hydrogen gas. c.Oxygen. d.Water vapor. e.Heat. Question 5 The circle on the left shows a magnified view of a very small portion of liquid water in a closed container. What would the magnified view on the right show after the water has all evaporated? Debate Splenda (sucralose) is the safest and best artificial sweetener. Aspartame is the safest and best artificial sweetener Saccharin is the safest and best artificial sweetener Acesulfame K is the safest and best artificial sweetener Chips Time Points Opening 2 4 min 6 Rebuttal 2 2 min 4 Question 1 1 30 sec 2 Answer 1 1 1 min 3 Question 2 1 30 sec 2 Answer 2 1 1 min 3 Question 3 1 30 sec 2 Answer 3 1 1 min 3 Closing 2 2 min 5 Scientific Studies ? Cite sources ? Electronic Data Bases: ? ISI Web of Science ? SciFinder ? Wansink, B.; Cheny M. M. Super Bowls: Serving Bowl Size and Food Consumption. JAMA, 2005, 293 (14), 1727-1728. Wansink, B.; Cheny M. M. Super Bowls: Serving Bowl Size and Food Consumption. JAMA, 2005, 293 (14), 1727-1728. Wansink, B.; Cheny M. M. Super Bowls: Serving Bowl Size and Food Consumption. JAMA, 2005, 293 (14), 1727-1728. Assignments Homework 1 Due Tuesday, 9/9 Debate in discussion 9/17 OR 9/19 Amy Gottfried W1, Lecture 2: F 9/7
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