The Scientific Method Say Thanks to the Authors Click http://www.ck12.org/saythanks (No sign in required) To access a customizable version of this book, as well as other interactive content, visit www.ck12.org CK-12 Foundation is a non-profit organization with a mission to reduce the cost of textbook materials for the K-12 market both in the U.S. and worldwide. Using an open-content, web-based collaborative model termed the FlexBook®, CK-12 intends to pioneer the generation and distribution of high-quality educational content that will serve both as core text as well as provide an adaptive environment for learning, powered through the FlexBook Platform®. Copyright © 2013 CK-12 Foundation, www.ck12.org The names “CK-12” and “CK12” and associated logos and the terms “FlexBook®” and “FlexBook Platform®” (collectively “CK-12 Marks”) are trademarks and service marks of CK-12 Foundation and are protected by federal, state, and international laws. Any form of reproduction of this book in any format or medium, in whole or in sections must include the referral attribution link http://www.ck12.org/saythanks (placed in a visible location) in addition to the following terms. Except as otherwise noted, all CK-12 Content (including CK-12 Curriculum Material) is made available to Users in accordance with the Creative Commons Attribution/Non- Commercial/Share Alike 3.0 Unported (CC BY-NC-SA) License (http://creativecommons.org/licenses/by-nc-sa/3.0/), as amended and updated by Creative Commons from time to time (the “CC License”), which is incorporated herein by this reference. Complete terms can be found at http://www.ck12.org/terms. Printed: August 25, 2013 www.ck12.org Concept 1. The Scientific Method CONCEPT 1 The Scientific Method Lesson Objectives • Describe the approaches used by the ancient Greek philosophers to understand the world around them. • Define inductive and deductive reasoning. • Name key individuals and groups who contributed to the science of chemistry. • Describe the scientific method. • Describe the rise and fall of the phlogiston theory. Lesson Vocabulary • inductive reasoning: Involves getting a collection of specific examples and drawing a general conclusion from them. • deductive reasoning: Takes a general principle and then draws a specific conclusion from the general concept. • scientific method: A process consisting of making observations, developing a hypothesis, and testing that hypothesis. • phlogiston: The substance that is lost from a material when it is burned. Check Your Understanding Recalling Prior Knowledge • How did ancient civilizations know what chemical processes to use? How Do We Know What We Know? Earth, Air, Fire, and Water Humans have always wondered about the world around them. One of the questions of interest was (and still is) what is this world made of? Among other definitions, chemistry has often been defined as the study of matter. What matter consists of has been a source of debate over the centuries. One of the key arenas for this debate in the Western world was Greek philosophy. Philosophy literally means “love of wisdom.” The Greek philosophers held a great deal of influence in society’s general knowledge and belies from about the seventh century to the first century B.C. As the Roman Empire became more powerful, Greek ideas were gradually supplanted by Roman ones. However, many of the ideas carried over into medieval Europe where they were reexamined along with the rise of modern scientific thought. In ancient Greece, the basic approach to answering questions about the world was through discussion and debate. There was very little gathering of information, and it was believed that the best way to answer fundamental questions 1 www.ck12.org was through reasoning and talking. As a result, several ideas about matter were put forth, but these ideas could not really be proven or disproven. For example, Thales of Miletus ( 625-545 B.C.) believed that water was the fundamental unit of matter, whereas Anaximenes ( 585-525 B.C.) felt that air was the basic unit. Empedocles ( 490- 430 B.C.) argued for the idea that matter was composed of earth, air, fire, and water. Each of these men had reasons they could offer to support their theories, but there was no way to prove who was right. The first major philosopher to gather data through observation was Aristotle (384-322 B.C., shown in Figure 1.1). He recorded many observations about the weather, the life and behaviors of plants and animals, physical motions, and a number of other topics. Aristotle could potentially be considered the first “real” scientist, because he made systematic observations of nature before trying to understand what he was seeing. Although Aristotle contributed greatly to Greek knowledge, not all of his observations led to correct theories. Leucippus ( 480-420 B.C.) and his student Democritus ( 460-370 B.C.) proposed some theories about matter that Aristotle later opposed. Since Aristotle’s influence was so great, others chose to reject these theories in favor of Aristotle’s ideas. However, it turned out that Aristotle was wrong and Leucippus and Democritus were right, but at the time there was no method for proving or disproving these opposing theories. It took almost 2000 years for people to reconsider this issue since Aristotle was held in such high regard by scholars. FIGURE 1.1 Aristotle 2 www.ck12.org Concept 1. The Scientific Method Inductive and Deductive Reasoning Two approaches to logical thinking developed over the centuries. These two methods are inductive reasoning and deductive reasoning. Inductive reasoning involves making specific observations, and then drawing a general conclusion. Deductive reasoning begins with a general principle and a prediction based on this principle; the prediction is then tested, and a specific conclusion can then be drawn. The first step in the process of inductive reasoning is making specific observations. In the periodic table of elements, which we will discuss later, there is a group of metals with similar properties called the alkali metals. The alkali metals include elements such as sodium and potassium. If I put sodium or potassium in water, I will observe a very violent reaction every time. I draw a general conclusion from these observations: all alkali metals will react violently with water. In deductive reasoning, I start with a general principle. For example, say I know that acids turn a special material called blue litmus paper red. I have a bottle of vinegar, which I believe is an acid, so I expect the litmus paper to turn red when I immerse it in the vinegar. When I dip the litmus paper in the vinegar, it does turn red, so I conclude that vinegar is in fact an acid. You can see that in order for deductive reasoning to lead to correct conclusions, the general principle you begin with must be true. I can only conclude that vinegar is an acid based on the accuracy of the general principle that acids turn blue litmus paper red. Inductive and deductive reasoning can be thought of as opposites. For inductive reasoning, we start with specific observations and draw a general conclusion. For deductive reasoning, we start with a general principle and use this principle to draw a specific conclusion. The Idea of the Experiment Inductive reasoning is at the heart of what we call the “scientific method.” In European culture, this approach was developed mainly by Francis Bacon (1561-1626), a British scholar. He advocated the use of inductive reasoning in every area of life, not just science. The scientific method as developed by Bacon and others involved several steps: 1. Ask a question – identify the problem to be considered. 2. Make observations – gather data that pertains to the question. 3. Propose an explanation (a hypothesis) for the observations. 4. Design and carry out ways to test the hypothesis. Note that this should not be considered a “cookbook” for scientific research. Scientists do not sit down with their daily “to do” list and write down these steps. The steps may not necessarily be followed in order, and testing a given explanation often leads to new questions and observations that can result in changes to the original hypothesis. However, this method does provide a general outline of how scientific research is usually done. During the early days of the scientific enterprise (up to the nineteenth century), scientists generally worked as individuals. They may have had an assistant to help with preparing materials, but their work was usually solitary. Their results might be disseminated in a letter to friends or at a scientific society meeting. Today the practice of science is very different. Research is carried out by teams of people, sometimes at a number of different locations. The details of methods and the results of the experiments are published in scientific journals and books, as well as being presented at local, national, or international meetings. Electronic publication on the Internet speeds up the process of sharing information with others. Before conclusions can be considered reliable, experiments and results must be replicated in other labs. In order for other scientists to know that the information is correct, the experiments need to be done in other labs to obtain the same results. Researchers in other labs may get ideas for new experiments that could confirm the original hypothesis. On the other hand, they may see flaws in the original thinking and experiments that would suggest the hypothesis was false. The modern scientific approach of carefully recording experimental procedures and data allows results to be tested and replicated to that everyone can have confidence in the final results. 3 www.ck12.org A good experiment must be carefully designed to test the hypothesis.