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The Scientific Method

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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 . • key individuals and groups who contributed to the of . • 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 , 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

• 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 literally “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 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 was (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 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 ( 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

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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 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 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

Inductive reasoning is at the heart of what we call the “scientific method.” In European culture, this approach was developed mainly by (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 (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 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.

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A experiment must be carefully designed to test the hypothesis. Let’s think back to our example of inductive reasoning in observing reactions with alkali metals and water. We believe that all alkali metals produce violent reactions with water. To test this hypothesis, we must design an experiment in which we can observe the reactions of each alkali metal with water. We will test each alkali metal: lithium, sodium, potassium, rubidium, cesium, and francium. In order for this experiment to produce consistent results, we should use the same amount of water and same size of these metals each time a test is formed. Based on our hypothesis, we expect a violent reaction to occur when any one of these metals is added to water. If a sample of lithium is added to our water and we observe a small explosion, our hypothesis is strengthened. If lithium is added to our water and nothing happens, our hypothesis must not be true. We can either modify our hypothesis to include this new data, or replace our hypothesis with a new one. When a hypothesis is confirmed repeatedly, it eventually becomes a theory. A theory is a general principle that is offered to explain a natural . A theory offers a of why something happens. Although theories, like hypotheses, can be disproved, it is more likely for a theory to be modified. However, while a hypotheses is a suggested explanation of a phenomena, a theory is a proved explanation based off of many hypotheses and much experimentation. Over time, theories evolve with new research and data, but are rarely discarded completely. A , on the other hand, is a that is always true, but does not include an explanation as to why. The law of gravity says a rock will fall when dropped, but it does not explain why (gravitational theory is very complex and incomplete at present). The kinetic-molecular theory of gases, on the other hand, tells us what happens when a gas is heated in a closed container (the pressure increases), but also explains why (the motions of the gas are increased due to the change in temperature). Theories do not get “promoted” to laws, because laws do not answer the “why” question.

Phlogiston - The Rise and Fall of a Theory

Early chemists spent a lot of time heating things and setting them on fire (on purpose, unlike some modern-day chemistry students). They observed that flammable materials tended to weigh less after being burned. As more materials were studied, this observation was found to be very consistent. A seemingly reasonable explanation for this phenomenon was that some substance was lost from the material when it was burned. This substance was named “phlogiston” from the Greek word ϕλoγιστ´ν (transliterated as phlogistón), which means “burning up.” The phlogiston theory was first put forth in 1667 by the German physician and alchemist Johann Joachim Becher (1635–1682, shown in Figure 1.2).

FIGURE 1.2 Johann Becher

Becher had taken the four ancient Greek elements (earth, air, fire, and water) and discarded fire and air. He expanded the “earth” category to three groups, one of which was involved in burning. In 1703, George Stahl, a German professor of medicine and chemistry, renamed this particular fraction of Becher’s earth as phlogiston.

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What was the that led to the development of this theory? One obvious experiment involved the burning of wood. The ashes remaining after the fire weighed considerably less than that original wood sample. Therefore, it seemed that phlogiston had been released during the burning process, leaving the “dephlogisticated” ashes behind. If wood or a candle was burned in a closed container, the fire would soon be extinguished. This was taken by supporters of the theory as evidence that air could only absorb so much phlogiston. Later, carbon dioxide gas was discovered and studied. An experiment was performed in 1772 that exhausted all the air in a container. Further burning of a candle and of phosphorus were then carried out in the container. After removing the carbon dioxide with an absorbent, a gas was found that did not support life or combustion. This gas (which we now know as nitrogen and which comprises about 78% of the atmosphere) was believed to be phlogiston. So far, so good. We have observations – things lose weight when they burn. We have an explanation – the original material loses phlogiston when it burns. What we don’t know is what phlogiston is or how much of it is in a given material. But are there other experiments that lead us in a different direction? Other scientists started to ask questions and run experiments. They noticed some results that seemed to contradict what would be expected if the phlogiston theory was correct. If magnesium is heated, the product (a solid) weighs more than the original magnesium metal. The explanation offered was that phlogiston had negative weight in this case. Can the same material have both a positive weight and a negative weight? When mercuric oxide was heated in the absence of any charcoal, it returned to its pure metal form. The phlogiston theory would require that charcoal (thought to be essentially pure phlogiston) be present to provide the phlogiston for restoring the metal. The French scientist Antoine Lavoisier (Figure below) carried out studies on oxygen (which had originally been discovered by Joseph Priestley, an ardent supporter of the phlogiston theory). Lavoisier found that when mercury was heated, it would become mercuric oxide and gain weight. When the mercuric oxide was heated, it returned to mercury and released a gas he identified as oxygen. He also carried out a number of experiments that conclusively demonstrated the essential role of oxygen in combustion processes.

FIGURE 1.3 Antoine Lavoisier and his wife Marie-Anne Pierrette Paulze, who was also a chemist and made contributions to the work of her husband.

FIGURE 1.4 The device used by Lavoisier to study the decomposition of mercuric oxide.

Eventually the phlogiston theory was replaced by the oxygen-based combustion ideas developed by Lavoisier and others. Today the theory is studied as an example of how to approach a scientific question and how one theory can

5 www.ck12.org be supplanted by another theory that more closely fits the data. It should also be noted that the phlogiston idea took time to develop, it took time to become accepted, and it took time for researchers to discard it in favor of a better theory.

Lesson Summary

• The early Greek philosophers spent a great deal of time talking about nature, but they did little or no actual exploration or investigation. • Inductive reasoning means developing a general conclusion from a collection of observations. • Deductive reasoning means making a specific statement based on a general principle. • Scientific method is a process consisting of making observations, developing a hypothesis, and testing that hypothesis. • Phlogiston theory is the disproven idea that materials lost phlogiston when they burned.

Lesson Review Questions

1. What was a major shortcoming of the approach taken by Greek philosophers to understanding the material world? 2. How did Aristotle improve this approach? 3. Define “inductive reasoning” and give an example. 4. Define “deductive reasoning” and give an example. 5. What is the difference between a hypothesis and a theory? 6. What is the difference between a theory and a law? 7. What was the major evidence that supported the phlogiston theory? 8. What was the major evidence that contradicted the phlogiston theory?

Further Reading / Supplemental Links

• Overview of the scientific method: http://www.sciencebuddies.org/science-fair-projects/project_scientific_m ethod.shtml • Research using the scientific method: http://www.teachersdomain.org/asset/drey07_int_scprocess/ • Lavoisier video: http://www.schooltube.com/video/5a2cb561ceabe931f2b5/Antoine-Lavoisier-the-man • Information about Lavoisier and phlogiston theory: http://cti.itc.virginia.edu/ meg3c/classes/tcc313/200Rpr ojs/lavoisier2/home.html

Points to Consider

Chemistry is the study of matter and the changes that matter can undergo.

• What is matter? • Where do you encounter matter in your everyday life? • What are the states of matter? • Can matter be changed?

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References

1. Photographer: Jastrow. http://commons.wikimedia.org/wiki/File:Aristotle_Altemps_Detail.jpg. Public Do- main 2.. http://commons.wikimedia.org/wiki/File:Jjbecher.jpg. Public Domain 3. Jacques-Louis David. http://commons.wikimedia.org/wiki/File:David_-_Portrait_of_Monsieur_Lavoisier_an d_His_Wife.jpg. Public Domain 4. Marie-Anne Pierrette Paulze. http://commons.wikimedia.org/wiki/File:Lavoisier_decomposition_air.png. Pub- lic Domain

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