Lecture notes on Chemistry

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Chapter 1 Chemistry, Matter, and Measurement Opening Essay In April 2003, the US Pharmacopeia, a national organization that establishes quality standards for medications, reported a case in which a physician ordered “morphine a powerful painkiller 2–3 mg IV intravenously every 2–3 hours for pain.” A nurse misread the dose as “23 mg” and thus administered approximately 10 times the proper amount to an 8-year-old boy with a broken leg. The boy stopped breathing but was successfully resuscitated and left the hospital three days later. Quantities and measurements are as important in our everyday lives as they are in medicine. The posted speed limits on roads and highways, such as 55 miles per hour (mph), are quantities we might encounter all the time. Both parts of a quantity, the amount (55) and the unit (mph), must be properly communicated to prevent potential problems. In chemistry, as in any technical endeavor, the proper expression of quantities is a necessary fundamental skill. As we begin our journey into chemistry, we will learn this skill so that errors—from homework mistakes to traffic tickets to more serious consequences—can be avoided. The study of chemistry will open your eyes to a fascinating world. Chemical processes are continuously at work all around us. They happen as you cook and eat food, strike a match, shampoo your hair, and even read this page. Chemistry is called the central science because a knowledge of chemical principles is essential for other sciences. You might be surprised at the extent to which chemistry pervades your life. 1.1 What Is Chemistry? LEARNING OBJECTIVES 1. Define chemistry in relation to other sciences. 2. Identify the general steps in the scientific method. Saylor URL: http://www.saylor.org/books Saylor.org 5 Chemistry is the study of matter—what it consists of, what its properties are, and how it changes. Being able to describe the ingredients in a cake and how they change when the cake is baked is called chemistry. Matter is anything that has mass and takes up space—that is, anything that is physically real. Some things are easily identified as matter—this book, for example. Others are not so obvious. Because we move so easily through air, we sometimes forget that it, too, is matter. Chemistry is one branch of science. Science is the process by which we learn about the natural universe by observing, testing, and then generating models that explain our observations. Because the physical universe is so vast, there are many different branches of science (Figure 1.1 "The Relationships between Some of the Major Branches of Science"). Thus, chemistry is the study of matter, biology is the study of living things, and geology is the study of rocks and the earth. Mathematics is the language of science, and we will use it to communicate some of the ideas of chemistry. Although we divide science into different fields, there is much overlap among them. For example, some biologists and chemists work in both fields so much that their work is called biochemistry. Similarly, geology and chemistry overlap in the field called geochemistry. Figure 1.1 "The Relationships between Some of the Major Branches of Science" shows how many of the individual fields of science are related. Figure 1.1 The Relationships between Some of the Major Branches of Science Saylor URL: http://www.saylor.org/books Saylor.org 6 Chemistry lies more or less in the middle, which emphasizes its importance to many branches of science. Note There are many other fields of science, in addition to the ones (biology, medicine, etc.) listed here. Looking Closer: Alchemy As our understanding of the universe has changed over time, so has the practice of science. Chemistry in its modern form, based on principles that we consider valid today, was developed in the 1600s and 1700s. Before that, the study of matter was known as alchemy and was practiced mainly in China, Arabia, Egypt, and Europe. Saylor URL: http://www.saylor.org/books Saylor.org 7 Alchemy was a somewhat mystical and secretive approach to learning how to manipulate matter. Practitioners, called alchemists, thought that all matter was composed of different proportions of the four basic elements—fire, water, earth, and air—and believed that if you changed the relative proportions of these elements in a substance, you could change the substance. The long-standing attempts to “transmute” common metals into gold represented one goal of alchemy. Alchemy’s other major goal was to synthesize the philosopher’s stone, a material that could impart long life—even immortality. Alchemists used symbols to represent substances, some of which are shown in the accompanying figure. This was not done to better communicate ideas, as chemists do today, but to maintain the secrecy of alchemical knowledge, keeping others from sharing in it. In spite of this secrecy, in its time alchemy was respected as a serious, scholarly endeavor. Isaac Newton, the great mathematician and physicist, was also an alchemist. E X A M P L E 1 Which fields of study are branches of science? Explain. 1. sculpture 2. astronomy Solution 1. Sculpture is not considered a science because it is not a study of some aspect of the natural universe. 2. Astronomy is the study of stars and planets, which are part of the natural universe. Astronomy is therefore a field of science. S K I L L - B U I L D I N G E X E R C I S E Saylor URL: http://www.saylor.org/books Saylor.org 8 Which fields of study are branches of science? 1. politics 2. physiology (the study of the function of an animal’s or a plant’s body) 3. geophysics 4. agriculture How do scientists work? Generally, they follow a process called the scientific method. The scientific method is an organized procedure for learning answers to questions. To find the answer to a question (for example, “Why do birds fly toward Earth’s equator during the cold months?”), a scientist goes through the following steps, which are also illustrated in Figure 1.2 "The General Steps of the Scientific Method": Figure 1.2 The General Steps of the Scientific Method Saylor URL: http://www.saylor.org/books Saylor.org 9 The steps may not be as clear-cut in real life as described here, but most scientific work follows this general outline. 1. Propose a hypothesis. A scientist generates a testable idea, or hypothesis, to try to answer a question or explain how the natural universe works. Some people use the word theory in place of hypothesis, but the word hypothesis is the proper word in science. For scientific applications, the word theory is a general statement that describes a large set of observations and data. A theory represents the highest level of scientific understanding. 2. Test the hypothesis. A scientist evaluates the hypothesis by devising and carrying out experiments to test it. If the hypothesis passes the test, it may be a proper answer to the question. If the hypothesis does not pass the test, it may not be a good answer. Saylor URL: http://www.saylor.org/books Saylor.org 10 3. Refine the hypothesis if necessary. Depending on the results of experiments, a scientist may want to modify the hypothesis and then test it again. Sometimes the results show the original hypothesis to be completely wrong, in which case a scientist will have to devise a new hypothesis. Not all scientific investigations are simple enough to be separated into these three discrete steps. But these steps represent the general method by which scientists learn about our natural universe. CONCEPT REVIEW EXERC ISES 1. Define science and chemistry. 2. Name the steps of the scientific method. ANSWERS 1. Science is a process by which we learn about the natural universe by observing, testing, and then generating models that explain our observations. Chemistry is the study of matter. 2. propose a hypothesis, test the hypothesis, and refine the hypothesis if necessary KEY TAKEAWAYS  Chemistry is the study of matter and how it behaves.  The scientific method is the general process by which we learn about the natural universe. EXERCISES 1. Based on what you know, which fields are branches of science? a. meteorology (the study of weather) Saylor URL: http://www.saylor.org/books Saylor.org 11 b. astrophysics (the physics of planets and stars) c. economics (the study of money and monetary systems) d. astrology (the prediction of human events based on planetary and star positions) e. political science (the study of politics) 2. Based on what you know, which fields are a branches of science? a. history (the study of past events) b. ornithology (the study of birds) c. paleontology (the study of fossils) d. zoology (the study of animals) e. phrenology (using the shape of the head to determine personal characteristics) 3. Which of the following are examples of matter? a. a baby b. an idea c. the Empire State Building d. an emotion e. the air f. Alpha Centauri, the closest known star (excluding the sun) to our solar system 4. Which of the following are examples of matter? a. your textbook b. brain cells c. love d. a can of soda e. breakfast cereal 5. Suggest a name for the science that studies the physics of rocks and the earth. Saylor URL: http://www.saylor.org/books Saylor.org 12 6. Suggest a name for the study of the physics of living organisms. 7. Engineering is the practical application of scientific principles and discoveries to develop things that make our lives easier. Is medicine science or engineering? Justify your answer. 8. Based on the definition of engineering in Exercise 7, would building a bridge over a river or road be considered science or engineering? Justify your answer. 9. When someone says, “I have a theory that excess salt causes high blood pressure,” does that person really have a theory? If it is not a theory, what is it? 10.When a person says, “My hypothesis is that excess calcium in the diet causes kidney stones,” what does the person need to do to determine if the hypothesis is correct? 11. Some people argue that many scientists accept many scientific principles on faith. Using what you know about the scientific method, how might you argue against that assertion? 12. Most students take multiple English classes in school. Does the study of English use the scientific method? ANSWERS 1. a. science b. science c. not science d. not science e. not science Saylor URL: http://www.saylor.org/books Saylor.org 13 3. a. matter b. not matter c. matter d. not matter e. matter f. matter 5. geophysics 7. Medicine is probably closer to a field of engineering than a field of science, but this may be arguable. Ask your doctor. 9. In scientific terms, this person has a hypothesis. 11. Science is based on reproducible facts, not blind belief. 1.2 The Classification of Matter LEARNING OBJECTIVES 1. Use physical and chemical properties, including phase, to describe matter. 2. Identify a sample of matter as an element, a compound, or a mixture. Part of understanding matter is being able to describe it. One way chemists describe matter is to assign different kinds of properties to different categories. Physical and Chemical Properties Saylor URL: http://www.saylor.org/books Saylor.org 14 The properties that chemists use to describe matter fall into two general categories. Physical properties are characteristics that describe matter. They include characteristics such as size, shape, color, and mass. Chemical properties are characteristics that describe how matter changes its chemical structure or composition. An example of a chemical property is flammability—a material’s ability to burn—because burning (also known as combustion) changes the chemical composition of a material. Elements and Compounds Any sample of matter that has the same physical and chemical properties throughout the sample is called a substance. There are two types of substances. A substance that cannot be broken down into chemically simpler components is an element. Aluminum, which is used in soda cans, is an element. A substance that can be broken down into chemically simpler components (because it has more than one element) is acompound (Figure 1.2 "The General Steps of the Scientific Method"). Water is a compound composed of the elements hydrogen and oxygen. Today, there are about 118 elements in the known universe. In contrast, scientists have identified tens of millions of different compounds to date. Note Sometimes the word pure is added to substance, but this is not absolutely necessary. By definition, any single substance is pure. The smallest part of an element that maintains the identity of that element is called an atom. Atoms are extremely tiny; to make a line 1 inch long, you would need 217 million iron atoms. The smallest part of a compound that maintains the identity of that compound is called a molecule. Molecules are composed of atoms that are attached together and behave as a unit. Scientists usually work with millions and millions of atoms and molecules at a time. When a scientist is working with large numbers of atoms or molecules at a time, the scientist is studying the macroscopic view of the universe. However, scientists can also describe chemical events on the level of individual atoms or molecules, which is referred to as the microscopic viewpoint. We will see examples of Saylor URL: http://www.saylor.org/books Saylor.org 15 both macroscopic and microscopic viewpoints throughout this book (Figure 1.3 "How Many Particles Are Needed for a Period in a Sentence?"). Figure 1.3 How Many Particles Are Needed for a Period in a Sentence? Although we do not notice it from a macroscopic perspective, matter is composed of microscopic particles so tiny that billions of them are needed to make a speck we can see with the naked eye. The ×25 and ×400,000,000 indicate the number of times the image is magnified. Mixtures A material composed of two or more substances is a mixture. In a mixture, the individual substances maintain their chemical identities. Many mixtures are obvious combinations of two or more substances, such as a mixture of sand and water. Such mixtures are called heterogeneous mixtures. In some mixtures, the components are so intimately combined that they act like a single substance (even though they are not). Mixtures with a consistent composition throughout are called homogeneous mixtures (or solutions). Sugar dissolved in water is an example of a solution. A metal alloy, such as steel, is an example of a solid solution. Air, a mixture of mainly nitrogen and oxygen, is a gaseous solution. EXAMPLE 2 Saylor URL: http://www.saylor.org/books Saylor.org 16 How would a chemist categorize each example of matter? 1. saltwater 2. soil 3. water 4. oxygen Solution 1. Saltwater acts as if it were a single substance even though it contains two substances—salt and water. Saltwater is a homogeneous mixture, or a solution. 2. Soil is composed of small pieces of a variety of materials, so it is a heterogeneous mixture. 3. Water is a substance; more specifically, because water is composed of hydrogen and oxygen, it is a compound. 4. Oxygen, a substance, is an element. SKILL-BUILDING EXERCISE How would a chemist categorize each example of matter? 1. coffee 2. hydrogen 3. an egg Phases Saylor URL: http://www.saylor.org/books Saylor.org 17 Another way to classify matter is to describe it as a solid, a liquid, or a gas, which was done in the examples of solutions. These three descriptions, each implying that the matter has certain physical properties, represent the three phases of matter. A solid has a definite shape and a definite volume. Liquids ordinarily have a definite volume but not a definite shape; they take the shape of their containers. Gases have neither a definite shape nor a definite volume, and they expand to fill their containers. We encounter matter in each phase every day; in fact, we regularly encounter water in all three phases: ice (solid), water (liquid), and steam (gas). We know from our experience with water that substances can change from one phase to another if the conditions are right. Typically, varying the temperature of a substance (and, less commonly, the pressure exerted on it) can cause a phase change, a physical process in which a substance goes from one phase to another (Figure 1.4 "Boiling Water"). Phase changes have particular names depending on what phases are involved, as summarized in Table 1.1 "Phase Changes". Table 1.1 Phase Changes Change Name solid to liquid melting, fusion solid to gas sublimation liquid to gas boiling, evaporation liquid to solid solidification, freezing gas to liquid condensation gas to solid deposition Saylor URL: http://www.saylor.org/books Saylor.org 18 Figure 1.5 "The Classification of Matter" illustrates the relationships between the different ways matter can be classified. Figure 1.5 The Classification of Matter Matter can be classified in a variety of ways, depending on its properties. CONCEPT REVIEW EXERCISES Saylor URL: http://www.saylor.org/books Saylor.org 19 1. Explain the differences between the physical properties of matter and the chemical properties of matter. 2. What is the difference between a heterogeneous mixture and a homogeneous mixture? Give an example of each. 3. Give at least two examples of a phase change and state the phases involved in each. ANSWERS 1. Physical properties describe the existence of matter, and chemical properties describe how substances change into other substances. 2. A heterogeneous mixture is obviously a mixture, such as dirt; a homogeneous mixture behaves like a single substance, such as saltwater. 3. solid to liquid (melting) and liquid to gas (boiling) (answers will vary) KEY TAKEAWAYS  Matter can be described with both physical properties and chemical properties.  Matter can be identified as an element, a compound, or a mixture. EXERCISES 1. Does each statement refer to a chemical property or a physical property? a. Balsa is a very light wood. b. If held in a flame, magnesium metal burns in air. c. Mercury has a density of 13.6 g/mL. d. Human blood is red. Saylor URL: http://www.saylor.org/books Saylor.org 20 2. Does each statement refer to a chemical property or a physical property? a. The elements sodium and chlorine can combine to make table salt. b. The metal tungsten does not melt until its temperature exceeds 3,000°C. c. The ingestion of ethyl alcohol can lead to disorientation and confusion. d. The boiling point of isopropyl alcohol, which is used to sterilize cuts and scrapes, is lower than the boiling point of water. 3. Define element. How does it differ from a compound? 4. Define compound. How does it differ from an element? 5. Give two examples of a heterogeneous mixture. 6. Give two examples of a homogeneous mixture. 7. Identify each substance as an element, a compound, a heterogeneous mixture, or a solution. a. xenon, a substance that cannot be broken down into chemically simpler components b. blood, a substance composed of several types of cells suspended in a salty solution called plasma c. water, a substance composed of hydrogen and oxygen Saylor URL: http://www.saylor.org/books Saylor.org 21 8. Identify each substance as an element, a compound, a heterogeneous mixture, or a solution. a. sugar, a substance composed of carbon, hydrogen, and oxygen b. hydrogen, the simplest chemical substance c. dirt, a combination of rocks and decaying plant matter 9. Identify each substance as an element, a compound, a heterogeneous mixture, or a solution. a. air, primarily a mixture of nitrogen and oxygen b. ringer’s lactate, a standard fluid used in medicine that contains salt, potassium, and lactate compounds all dissolved in sterile water c. tartaric acid, a substance composed of carbon, hydrogen, and oxygen 10. Identify each material as an element, a compound, a heterogeneous mixture, or a solution. a. equal portions of salt and sand placed in a beaker and shaken up b. a combination of beeswax dissolved in liquid hexane c. hydrogen peroxide, a substance composed of hydrogen and oxygen 11. What word describes each phase change? a. solid to liquid b. liquid to gas c. solid to gas Saylor URL: http://www.saylor.org/books Saylor.org 22 12. What word describes each phase change? a. liquid to solid b. gas to liquid c. gas to solid ANSWERS 1. a. physical property b. chemical property c. physical property d. physical property 3. An element is a substance that cannot be broken down into chemically simpler components. Compounds can be broken down into simpler substances. 5. a salt and pepper mix and a bowl of cereal (answers will vary) 7. a. element b. heterogeneous mixture c. compound 9. a. solution b. solution Saylor URL: http://www.saylor.org/books Saylor.org 23 c. compound 11. a. melting or fusion b. boiling or evaporation c. sublimation 1.3 Measurements LEARNING OBJECTIVE 1. Express quantities properly, using a number and a unit. A coffee maker’s instructions tell you to fill the coffeepot with 4 cups of water and use 3 scoops of coffee. When you follow these instructions, you are measuring. When you visit a doctor’s office, a nurse checks your temperature, height, weight, and perhaps blood pressure (Figure 1.6 "Measuring Blood Pressure"). The nurse is also measuring. Chemists measure the properties of matter and express these measurements as quantities. A quantity is an amount of something and consists of a number and a unit. The number tells us how many (or how much), and the unit tells us what the scale of measurement is. For example, when a distance is reported as “5 kilometers,” we know that the quantity has been expressed in units of kilometers and that the number of kilometers is 5. If you ask a friend how far he or she walks from home to school, and the friend answers “12” without specifying a unit, you do not know whether your friend walks—for example, 12 miles, 12 kilometers, 12 furlongs, or 12 yards. Both a number and a unit must be included to express a quantity properly. Saylor URL: http://www.saylor.org/books Saylor.org 24

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