General Chemistry 1 - Pure Substances and Mixtures PDF

Lesson 1.3 Pure Substances and Mixtures Contents Introduction 1 Learning Objectives 2 Warm Up 2 Learn about It! 4 Classification of Matter 4 Pure Substances 6 Elements 7 Comp...

Lesson 1.3 Pure Substances and Mixtures Contents Introduction 1 Learning Objectives 2 Warm Up 2 Learn about It! 4 Classification of Matter 4 Pure Substances 6 Elements 7 Compounds 13 Mixtures 16 Homogeneous Mixtures 17 Heterogeneous Mixtures 19 Key Points 20 Check Your Understanding 21 Challenge Yourself 24 Photo Credits 24 Bibliography 25 Unit 1: Matter Lesson 1.3 Pure Substances and Mixtures Introduction Have you been to a buffet? It is a system of serving meals in the restaurant wherein different viands are placed on the table, and diners serve themselves. Like a buffet, the world offers variety in terms of materials that can be encountered. Some materials like rocks, wood, and water are visible while air is not. Some materials are pure in terms of their composition, while other materials are combinations of two or more substances. There is so much diversity of materials in the environment, forcing scientists to classify matter into different groups. 1.3 Pure Substances and Mixtures 1 Unit 1: Matter In this lesson, you will learn the different classification of matter. Matter may be classified according to its composition. Materials with a fixed composition are known as pure substances, while those with varying compositions are known as mixtures. Pure substances may be further classified as elements and compounds, while mixtures may be grouped as homogeneous or heterogeneous. Each group of matter has its unique properties that allow them to be distinguishable from other kinds of material. Learning Objectives DepEd Competency This serves as a prerequisite or enrichment for the given competency: In this lesson, you should be able to do the Differentiate between pure following: substances and mixtures Differentiate pure substances (STEM_GC11MP-Ia-b-6). from mixtures. Categorize pure substances as elements and compounds. Enumerate the classifications of mixtures. Warm Up Classifying Matter 30 minutes Matter may be classified as solids, liquids, or gases. Matter may also be grouped according to the properties they possess. Another way to classify matter is by investigating its composition. Materials baking soda table salt fine sand 1.3 Pure Substances and Mixtures 2 Unit 1: Matter iron filings sulfur powder 6 watch glasses nuts bolts bar magnet magnifying glass metal strainer Procedure 1. Place a teaspoon of each sample on a watch glass. Label each sample accordingly. a. Sample 1 - iron filings b. Sample 2 - sulfur c. Sample 3 - baking soda d. Sample 4 - table salt e. Sample 5 - fine sand and baking soda f. Sample 6 - iron filings and table salt 2. Examine each sample. Use a magnifying glass to describe its appearance. 3. Place a magnet near each sample and observe if the magnet can separate its components. 4. Let each sample pass through the strainer and see if its components can be separated or not. 5. Record all your observations in the table below. Guide Questions 1. How will you describe the appearance of each sample? 2. How will you describe the composition of each sample? 3. Why do you think the components of Samples 5 and 6 can be separated by physical means? 4. Based on the activity, how will you differentiate pure substances from mixtures? 1.3 Pure Substances and Mixtures 3 Unit 1: Matter Data Table Table 1.3.1. Summary of observable characteristics of different samples of matter Can its components Does it have a Does it have be Is it a pure Is it a Sample uniform a fixed separated substance? mixture? appearance? composition? by physical means? 1 2 3 4 5 6 Learn about It! Classification of Matter There is diversity in the materials that are present in the environment. These materials vary in characteristics as well as in the purpose they serve. Thus, it is important to classify these materials to recognize them and determine their uses easily. How can matter be classified? Matter may be classified according to their state or phase. The three states of matter are solid, liquid, and gas. Solid materials are rigid and have a definite shape. Liquids, on the other hand, have a definite volume but no definite shape. Unlike solids, liquids tend to 1.3 Pure Substances and Mixtures 4 Unit 1: Matter follow the shape of its container and are able to flow with ease. Lastly, gases have no definite shape and volume. Gases are often invisible but are highly compressible compared to solids and liquids. coins liquids in flasks gas emitted in factories Fig. 1.3.1. Matter can be grouped into solids, liquids, or gases. Matter may be classified according to their properties. Properties are characteristics that a certain material possesses which makes it unique. Materials may possess physical properties or characteristics that are observable even without changing the composition of matter. Thus, matter may be classified according to their color, mass, volume, density, and other physical characteristics. On the other hand, matter also possesses characteristics that can only be observed once a material undergoes a chemical reaction. These properties are known as chemical properties. Materials around may be grouped according to their flammability, reactivity, and biodegradability. flowers grouped according dolls arranged by size blocks of wood of different to color shapes Fig. 1.3.2. Materials may be classified according to color, size, and shape which are known as physical properties. 1.3 Pure Substances and Mixtures 5 Unit 1: Matter fruit peelings as biodegradable plastics as nonbiodegradables Fig. 1.3.3. Materials may be classified according to their biodegradability which is a chemical property. Matter may be classified according to their composition. All matter is composed of tiny particles called atoms. However, the composition of atoms in a matter varies. Substances have a fixed or definite composition. This kind of matter is made up of a specific number of atoms or groups of atoms that are combined through a chemical reaction. Mixtures, on the other hand, are combinations of two or more substances. What are pure substances and mixtures? Pure Substances A pure substance is a kind of matter with a definite or fixed composition. Note that all materials are composed of atoms. Thus, pure substances are made up of atoms, too. However, they can be composed of a specific type of atom or combination of atoms. This composition is fixed for this kind of matter. A pure substance also has definite physical and chemical properties such as appearance, melting point, and reactivity. Regardless of the amount of pure substance, it will always have the same properties because it is made up of one type of particle. 1.3 Pure Substances and Mixtures 6 Unit 1: Matter Pure substances are classified into elements and compounds. An element is made up of one kind of atom, or two or more of the same kind of atoms that are chemically combined. On the other hand, a compound is made up of different kinds of atoms that are combined through a chemical reaction. Compounds have different properties from the elements that make them up. (a) atoms of an element (b) molecules of an element (c) molecules of a compound Fig. 1.3.4. An element is composed of only one type of atom while a compound is composed of two or more different kinds of atoms that are chemically combined. Elements Elements are the simplest substances because they are made up of only one kind of atom. It is a pure substance that is composed of only one type of atom. The atoms of one element are different from those of another element. For example, the element copper is composed only of copper atoms, while the element iron is composed only of iron atoms. copper iron Fig. 1.3.5. Elements of different kinds also differ in the atoms that make them up. 1.3 Pure Substances and Mixtures 7 Unit 1: Matter An element cannot be decomposed into simpler substances by physical or chemical means. Thus, it is not possible to alter the identity of a certain element through ordinary chemical reactions. Physical changes such as melting, freezing, or cutting do not change the identity of pure substances. Take, for example, the case of gold, a metallic element that is often used for jewelry. Gold is malleable and has a low melting point, which makes it a suitable material for jewelry making. Heating a sheet of gold to shape it into a ring will not change it into another substance. It is still gold but with different shapes and sizes. Fig. 1.3.6. Gold is a metallic element that is commonly used for making jewelry. Since elements are the simplest forms of substance, they are also considered as the building blocks of matter. This is because when elements react with one another, a new substance in the form of a compound is formed. Fig. 1.3.7, Water (H2O) is formed when two atoms of hydrogen (H) combined with one atom of oxygen (O). 1.3 Pure Substances and Mixtures 8 Unit 1: Matter There are 118 elements known to exist in which 94 of these occur naturally on Earth, while the remaining 24 are synthetic. Each element has a place in an arrangement called the periodic table of elements. Each element has its own chemical name and symbol. A chemical symbol consists of one to three letters. The first letter is always capitalized, and the other letters are always set in lowercase. The first letter is usually the first letter of the element name, while the second letter is usually the second letter of the element name. For instance, the chemical symbol for Oxygen is O, while the chemical symbol for Calcium is Ca. Some chemical symbols are taken from the Latin names of the given element. Table. 1.3.2 shows a list of the elements and their symbols from their Latin names. Table 1.3.2. List of elements and their symbols from their Latin names. Element Symbol Latin name antimony Sb stibium copper Cu cuprum gold Au aurum iron Fe ferrum lead Pb plumbum mercury Hg hydrargyrum potassium K kalium silver Ag argentum sodium Na natrium tin Sn stannum tungsten W wolfram A periodic table is a useful tool that can help in identifying elements that exhibit similar properties. The table classifies the elements into three general categories: metals, nonmetals, and metalloids. 1.3 Pure Substances and Mixtures 9 Unit 1: Matter Fig. 1.3.8. The periodic table of elements is the arrangement of all known elements according to their chemical properties. Metals start at the left and make up most of the elements in the periodic table. In fact, all elements to the left of the staircase-like line in the periodic table (except hydrogen) are generally classified as metals. Nonmetals are at the right part of the periodic table and are often shaded with different colors to distinguish them from metals. The metalloids lie between the metals and nonmetals. These elements form the staircase-like line in the periodic table. Metals have properties that distinguish them from nonmetals. For instance, metals (except mercury) are solid at room temperature. Metals have luster or the property that makes them shiny. Most metals exhibit malleability or a property that enables metals to be hammered into thin sheets without breaking. Metals also possess ductility or the ability to be drawn into wires. Also, metals are good conductors of heat and electricity. This is the reason why metals are good raw materials for making cooking pans, pots, and electrical wirings. 1.3 Pure Substances and Mixtures 10 Unit 1: Matter Fig. 1.3.9. Silver, platinum, and tungsten are examples of metals. Did You Know? Mercury is the only metal that is liquid at room temperature. It is a shiny, silvery liquid metal that forms beads due to its high surface tension. Mercury is also known as quicksilver due to its appearance and mobility. Fig. 1.3.10. Mercury has a high surface tension that enables it to form beads when separated. Some metals like iron, nickel, and cobalt possess magnetic properties. These magnetic materials are used in electric motors, generators and transformers, and storage devices such as tape recorders and hard disks. 1.3 Pure Substances and Mixtures 11 Unit 1: Matter hard disk speaker cassette tape Fig. 1.3.11. Examples of materials that utilize magnetic metals to function. Nonmetals, on the other hand, are the opposite of metals. Generally, nonmetals are either gaseous or dull solids. These elements are brittle as they break apart easily when subjected to a heavy blow. Nonmetals are poor conductors of heat and electricity. The major elements in living things such as carbon, hydrogen, oxygen, nitrogen, and sulfur are all nonmetals. Fig. 1.3.12. Bromine is the only nonmetal that is liquid at room temperature. Metalloids (or semimetals) are elements that exhibit properties of both metals and nonmetals. Some metalloids are shiny like metal but are also brittle like a nonmetal. Metalloids can conduct heat and electricity but not as good as how metals act as conductors. This is the reason why metalloids are known as semiconductors. 1.3 Pure Substances and Mixtures 12 Unit 1: Matter Fig. 1.3.13. Silicon and germanium are metalloids that are widely used in the manufacture of computer chips. How can elements be broken down into much simpler forms? Compounds Compounds are pure substances that are composed of two or more different elements that are combined in a fixed ratio by a chemical reaction. Many compounds are formed naturally due to geologic processes on Earth, while some compounds are formed when an element reacts with one of the gaseous elements in the air. Some compounds are products of chemical reactions between two or more compounds. Living things, like plants, produce glucose, an organic compound, during photosynthesis. The elements that comprise a compound exist in a fixed mass ratio. Recall that water has hydrogen and 1.3 Pure Substances and Mixtures 13 Unit 1: Matter oxygen. Each molecule of water has two atoms of hydrogen and one atom of oxygen. The three atoms are tightly held by a strong, attractive force. The chemical bonds that hold atoms together in a compound cannot be broken easily. However, unlike elements, compounds can be broken down into simpler forms by means of a chemical reaction. For instance, when an electric current is passed through water, a chemical change takes place. The atoms of water molecules break apart into two elements - hydrogen and oxygen. Fig. 1.3.15. In water electrolysis, an electric current is passed through water to separate its components to oxygen and hydrogen. When elements combine to form compounds, their identities change as well. A chemical change alters the identity of the substance. The properties of elements that make up a compound are different from the properties of the compound formed. For instance, table salt has a chemical name sodium chloride (NaCl) as it is composed of one atom of sodium and one atom of chlorine. Table salt is often used as a food additive, but sodium alone is explosive, while chlorine can be toxic. Thus, this shows that the chemical reaction between sodium and chlorine, both highly reactive elements, can produce a compound that is edible. 1.3 Pure Substances and Mixtures 14 Unit 1: Matter Fig. 1.3.16. Table salt or sodium chloride is a compound formed when sodium and chlorine combined together through a chemical reaction. Compounds may be classified according to the specific elements that are present. Organic compounds are substances that contain the elements carbon and hydrogen. The term “organic” is often associated with the word natural as it was believed before that only living things can produce organic compounds. However, scientists eventually discovered that organic compounds could also be produced artificially in laboratories. Most organic compounds are present in the food that the body needs in order to thrive. These organic compounds are carbohydrates, proteins, lipids, and nucleic acids. Inorganic compounds are substances that do not have carbon-hydrogen bonds. Carbon dioxide, water, and table salt are all examples of inorganic compounds. Fig. 1.3.17. The food that a person eats provides the organic compounds that the body needs in order to grow and survive. 1.3 Pure Substances and Mixtures 15 Unit 1: Matter How do compounds differ from elements? Mixtures Mixtures consist of two or more substances that are combined physically. When two or more substances are put together, they form a mixture if there is no chemical reaction that took place between them. For example, water and table salt are both compounds. When table salt is dissolved in water, a brine or salt solution is formed. The water and salt retain their properties even though they are mixed together. The brine tastes salty because of the presence of salt, but it also remains clear due to the characteristic of water. Fig. 1.3.18. Seawater is a mixture of dissolved salts and water. Unlike elements and compounds, mixtures are not pure substances. Instead, mixtures contain more than one type of substance. Each substance in a mixture has the same chemical make up it had before the mixture is formed. Also, mixtures do not have definite proportions. The amount of substances present in a mixture varies depending on the number of combined substances. For example, a person who prefers to drink a strong coffee will add less sugar in it than a person who prefers to drink a sweeter one. Because of this, mixtures do not have definite properties. The properties of mixtures depend on the substances that are present in it. 1.3 Pure Substances and Mixtures 16 Unit 1: Matter Mixtures may be further classified as homogeneous or heterogeneous. Each type of mixture has unique characteristics that set them apart from one another. Homogeneous Mixtures A homogeneous mixture consists of particles that are evenly spread out or distributed. The components of a homogeneous mixture cannot be distinguished from each other. This is because the particles of the components of a homogeneous mixture are so small that they cannot be seen by the naked eye. Homogeneous mixtures are also known as solutions. A solution is composed of a solute and a solvent. The solute is the substance that is dissolved by another substance, while the solvent is the dissolving medium in which the solute dissolves. In a typical solution, the solvent is the most abundant substance, while solute exists in smaller amounts. Substances that dissolve in a given solvent are soluble. For instance, salt and sugar are both soluble in water since these substances dissolve when mixed thoroughly with water. Liquids that are soluble in each other at all proportions are miscible. Alcohol and water mix well as they are miscible, contrary to oil and water which are immiscible. When a solute dissolves in a solvent, its particles are pulled away from one another. The particles of the solvent penetrate the space between solute particles. As the solvent particles continue to surround the solute particles, both components are evenly spread out, creating a homogeneous mixture. 1.3 Pure Substances and Mixtures 17 Unit 1: Matter Fig. 1.3.20. Solutes dissolved in a solvent when the solute particles are pulled away from one another, and the solvent particles continue to surround it until they are evenly spread out. Solutions may be solid, liquid, or gas. Most solutions are in the liquid phase. Solutions in which the solvent is water is known as aqueous solutions. Some examples of aqueous solutions are wine, alcohol, and soft drink. Fig. 1.3.21. Wine is a solution of alcohol and water while soft drink consists of dissolved carbon dioxide and sugars in water. 1.3 Pure Substances and Mixtures 18 Unit 1: Matter On the other hand, solid solutions are called alloys or mixtures of metals with other metals or nonmetals. Metals are combined with other substances to improve their durability. Fig. 1.3.22. Steel (left) is an alloy that is made up of iron and carbon. Brass (right) is an alloy of copper and zinc. Unpolluted air is a gaseous solution. Air is composed of different gases in varying proportions - nitrogen (78%), oxygen (21%), and other gases (1%). Heterogeneous Mixtures A heterogeneous mixture consists of particles that are not evenly distributed throughout. The components of a heterogeneous mixture can be distinguished from each other. Heterogeneous mixtures can be classified as suspensions or colloids. Colloids are heterogeneous mixtures with particles that are bigger than those of a solution but smaller than those of a suspension. The particles of colloids do not settle even after being left to stand for a long time. This is the reason why colloidal particles can exhibit Tyndall effect, a phenomenon wherein light is scattered. Some examples of colloids are mayonnaise, hair gel, and blood. 1.3 Pure Substances and Mixtures 19 Unit 1: Matter Fig. 1.3.23. Due to the spaces between colloidal particles, light is able to pass through and scatter in a colloid. Suspensions are heterogeneous mixtures with suspended particles that are large enough to be seen by the naked eye. Due to the size of the particles of a suspension, they are greatly affected by gravity, causing them to settle at the bottom of the container. For instance, a can of pineapple juice needs to be shaken well before drinking so that its pulp will mix well with the juice before drinking. Remember To easily distinguish the types of mixtures, always refer to the uniformity of its appearance. Homogeneous mixtures have a uniform appearance, while heterogeneous mixtures are not uniform in terms of its appearance. Key Points ___________________________________________________________________________________________ Matter may be classified according to their composition. The two major classifications of matter are pure substances and mixtures. ○ A pure substance is a kind of matter with a definite or fixed composition. An element is the simplest form of matter made up of one type of atom. 1.3 Pure Substances and Mixtures 20 Unit 1: Matter A compound is made up of different kinds of atoms that are combined through a chemical reaction. ○ Mixtures consist of two or more substances that are combined physically. A homogeneous mixture, also known as solution, consists of particles that are evenly spread out or distributed. A heterogeneous mixture consists of particles that are not evenly distributed throughout. ___________________________________________________________________________________________ Check Your Understanding A. Match each description to the correct term. _______ 1. a substance that is made up of only one kind of A. alloys atom B. colloids _______ 2. a substance that is composed of two or more C. compound different kinds of elements D. element _______ 3. also known as homogeneous mixtures _______ 4. elements that are good conductors of heat and E. inorganic electricity F. organic _______ 5. also known as semimetals 1.3 Pure Substances and Mixtures 21 Unit 1: Matter _______ 6. compound that contains the elements, carbon, G. metals and hydrogen H. metalloids _______ 7. heterogeneous mixtures with intermediate particles that exhibit Tyndall effect I. nonmetals _______ 8. dissolving medium in a solution J. solute _______ 9. substances that are dissolved in a solution K. solution _______ 10. solid solutions that are composed of metals and other elements L. solvent M. suspension B. Tell whether the statement is true or false. __________ 1. Similar to compounds, elements can be broken down into simpler forms. __________ 2. Mixtures are composed of substances that are physically combined. __________ 3. Components of mixtures can be separated through physical means. __________ 4. Solutions that have water as solvent are said to be aqueous. __________ 5. Suspensions are heterogeneous mixtures that have particles that can scatter light as it passes through them. C. Classify the following materials either as an element, a compound, or a mixture. ___________________ 1. zinc 1.3 Pure Substances and Mixtures 22 Unit 1: Matter ___________________ 2. sulfur ___________________ 3. mayonnaise ___________________ 4. baking soda ___________________ 5. coins 1.3 Pure Substances and Mixtures 23 Unit 1: Matter Challenge Yourself A. Answer the following questions. 1. How can you easily distinguish homogeneous mixtures from heterogeneous mixtures? 2. Which type of mixture has components that are easiest to separate? Why? B. Answer the following questions. 3. Why do some medications require you to shake them well before drinking? 4. Why is it possible to see a beam of sunlight between clouds and the ground? C. Answer the given question. 5. How would you know if the given element is metal, nonmetal, or metalloid? Cite a simple experiment that you can design to determine the kind of a given mystery element. Photo Credits Silver, by High Res Images of Chemical Elements is licensed under CC BY 3.0 via Wikimedia Commons. Platinum-nugget, by Alchemist-hp is licensed under CC BY-SA 3.0 via Wikimedia Commons. Tungsten element, by W. Oelen is licensed under CC BY 3.0 via Wikimedia Commons. Bromine 25ml, by W. Oelen is licensed under CC BY 3.0 via Wikimedia Commons. SaltinWaterSolution, by Chris 73 is licensed under CC BY 3.0 via Wikimedia Commons. 1.3 Pure Substances and Mixtures 24 Unit 1: Matter Bibliography Chang, Raymond, and Kenneth A. Goldsby. General Chemistry: The Essential Concepts. New York: McGraw-Hill, 2014. Handwerker, Mark J. Science Essentials. San Francisco, CA.: Jossey-Bass, 2005. Hawe, Alan, Dan Davies, Kendra McMahon, Lee Towler, Chris Collier, and Tonie Scott. Science 5–11: A Guide for Teachers. 2nd ed. New York, NY: David Fulton Publishers, 2009. Petrucci, Ralph H. General Chemistry: Principles and Modern Applications. Toronto, Ont.: Pearson Canada, 2011. Silberberg, Martin S. Principles of General Chemistry. New York: McGraw-Hill, 2013. 1.3 Pure Substances and Mixtures 25