Chemistry
Amount of Substance
Amount of substance refers to the quantity of a particular substance, measured in moles. It is a fundamental concept in chemistry and is used to quantify the number of atoms, molecules, or ions in a sample. The amount of substance is crucial for understanding chemical reactions and stoichiometry.
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eBook - ePubFoundations for Teaching Chemistry
Chemical Knowledge for Teaching
- Keith S. Taber(Author)
- 2019(Publication Date)
- Routledge(Publisher)
7 The most fundamental chemical concept: SubstanceAs suggested in Chapter 6 , a canonical understanding of chemistry depends upon appreciating what chemists mean by something being a substance. The ‘substance’ concept is a prerequisite for understanding other core chemical concepts such as ‘element’ and ‘compound’ (see Chapter 8 ) and ‘chemical reaction’ (see Chapter 11 ).The notion of a substanceOne of the most basic concepts in chemistry is that of substance. Chemistry is fundamentally the science that studies the properties of substances, including (indeed, especially) how they interact. Before we can do chemistry, we need a notion of what we mean by ‘substance’. In everyday use, substance may refer to anything substantial (as opposed to something ephemeral or imaginary): the earth, the table, an apple. So, any ‘stuff’ may be considered to have substance.Matter, materials, and substances
In chemistry, however, we distinguish matter (‘stuff’ generally) from substances that are considered to be particular kinds of stuff. Some familiar materials are effectively single substances: diamonds, table salt, baking soda, aluminium foil. But most materials met outside of the chemistry laboratory are not single substances in this way. Air is not a substance, nor is sea water (if tap water in some parts of the world comes pretty close). The soil is certainly not a ‘pure’ substance. Organic materials – hair, bone, wood – are complex materials and not substances. Some metal objects we come across in everyday use are close to being composed of a pure substance, but most are alloys which are mixtures. Very few metals (examples would be gold, silver, sometimes copper) are found native, and the minerals that are the sources of ores are often not single substances either.By contrast, a well-stocked chemical cupboard may contain a wide range of pure substances, and it is these that are the usual focus of laboratory work in school chemistry. Those reagents, however, have nearly always been produced by industrial processes. These processes have, at least, separated out the substance from others with which it was mixed in natural sources and have, in many cases, used chemical reactions to produce a substance difficult to source from, or even not found to exist in, the natural environment.
eBook - PDFFoundations of Chemistry
An Introductory Course for Science Students
- Philippa B. Cranwell, Elizabeth M. Page(Authors)
- 2021(Publication Date)
- Wiley(Publisher)
3 Amount of Substance At the end of this chapter, students should be able to: • Determine relative atomic and molecular masses using the periodic table of the elements • Explain the meaning of the mole and use Avogadro ’ s number to calculate numbers of atoms of elements or molecules of substances in a certain amount in moles • Use the equation relating the Amount of Substances in moles to mass and molar mass to calculate any one of these parameters knowing the other two • Calculate theoretical and actual percentage yields in chemical reactions • Calculate percentage composition by mass of elements in compounds from the molecular formula and relative atomic masses • Calculate percentage purity of compounds from analytical data relating to percentage composition • Determine the empirical and molecular formula of a compound from its percentage composition by mass • Calculate the concentration of a solution in various units, knowing its composition • Perform calculations to determine how to dilute a concentrated solution to a given molarity • Carry out calculations using titration data to determine the concentration of a solution • Use the molar gas volume to work out the mass of a certain volume of a known gas under standard conditions of temperature and pressure Foundations of Chemistry: An Introductory Course for Science Students , First Edition. Philippa B. Cranwell and Elizabeth M. Page. © 2021 John Wiley & Sons Ltd. Published 2021 by John Wiley & Sons Ltd. Companion website: www.wiley.com/go/Cranwell/Foundations 3.1 Masses of atoms and molecules Atoms join together to make molecules, and molecules react together to make different molecules or join together to make bigger molecules. In making these new substances, scientists need to know how much of one molecule or com-pound will react with another and how much product will be obtained as a result. To achieve this, we need to be able to count molecules or groups of mole-cules.
eBook - PDF- Paul Flowers, Klaus Theopold, Richard Langley, William R. Robinson(Authors)
- 2019(Publication Date)
- Openstax(Publisher)
For example, water, H 2 O, and hydrogen peroxide, H 2 O 2 , are alike in that their respective molecules are composed of hydrogen and oxygen atoms. However, because a hydrogen peroxide 120 3 • Composition of Substances and Solutions Access for free at openstax.org molecule contains two oxygen atoms, as opposed to the water molecule, which has only one, the two substances exhibit very different properties. Today, sophisticated instruments allow the direct measurement of these defining microscopic traits; however, the same traits were originally derived from the measurement of macroscopic properties (the masses and volumes of bulk quantities of matter) using relatively simple tools (balances and volumetric glassware). This experimental approach required the introduction of a new unit for Amount of Substances, the mole, which remains indispensable in modern chemical science. The mole is an amount unit similar to familiar units like pair, dozen, gross, etc. It provides a specific measure of the number of atoms or molecules in a sample of matter. One Latin connotation for the word “mole” is “large mass” or “bulk,” which is consistent with its use as the name for this unit. The mole provides a link between an easily measured macroscopic property, bulk mass, and an extremely important fundamental property, number of atoms, molecules, and so forth. A mole of substance is that amount in which there are 6.02214076 10 23 discrete entities (atoms or molecules). This large number is a fundamental constant known as Avogadro’s number (N A ) or the Avogadro constant in honor of Italian scientist Amedeo Avogadro. This constant is properly reported with an explicit unit of “per mole,” a conveniently rounded version being 6.022 10 23 /mol. Consistent with its definition as an amount unit, 1 mole of any element contains the same number of atoms as 1 mole of any other element.
eBook - PDF- Leo J. Malone, Theodore O. Dolter(Authors)
- 2012(Publication Date)
- Wiley(Publisher)
PART A SUMMARY KEY TERMS 5-2.1 The unit of quantity in chemistry is known as the mole (mol) and represents Avoga- dro’s number of particles. p. 151 5-2.2 The molar mass of an element is the atomic weight in grams. p. 152 5-3.1 The formula weight of a compound is the sum of the atomic weights of its component atoms expressed in amu. p. 156 5-3.3 The molar mass of a compound is the formula weight expressed in grams. p. 157 OBJECTIVES 5-4 Given the formula of a compound, determine the mole, mass, and percent composition of its elements. 5-5 Given the percent or mass composition determine the empirical formula and also the molecular formula if the molar mass is provided. SETTING A GOAL ■ n You will learn the relationship between the formu- la of a compound and its elemental composition. Part B The Component Elements of Compounds 5-4 The Composition of Compounds 161 TABLE 5-2 The Composition of One Mole of H 2 SO 4 NUMBER OF ATOMS MOLES OF ATOMS MASS OF ATOMS 1.204 * 10 24 H atoms d 2 mol H S 2.016 g H 6.022 * 10 23 S atoms d 1 mol S S 32.07 g S 2.409 * 10 24 O atoms d 4 mol O S 64.00 g O Totals: 4.215 * 10 24 atoms in 7 mol atoms in 6.022 * 10 23 molecules d one mole of molecules S 98.09g 5-4 The Composition of Compounds LOOKING AHEAD! The formula of a compound relays a wealth of information about the component elements. We will now look deeper into how the component parts of a compound relate to its formula. n One plus two equals one? At first glance this seems like bad math. However, we do know that one frame plus two wheels equals one bicycle. So in the context of the relationship of parts to the whole, the math works. Likewise, one carbon atom plus two oxygen atoms equals one molecule of carbon dioxide. Now consider the compound sulfuric acid (H 2 SO 4 ). In Table 5-2, we have illustrated the relation of one mole of compound to all its component parts. All of these relationships can be used to construct conversion factors between the compound and its elements.
eBook - PDF- Paul Flowers, Klaus Theopold, Richard Langley, William R. Robinson(Authors)
- 2015(Publication Date)
- Openstax(Publisher)
has a definite shape, and has a fairly constant volume specialized language used to represent components of the macroscopic and microscopic domains, such as chemical symbols, chemical formulas, chemical equations, graphs, drawings, and calculations well-substantiated, comprehensive, testable explanation of a particular aspect of nature estimate of amount by which measurement differs from true value standard of comparison for measurements ratio of equivalent quantities expressed with different units; used to convert from one unit to a different unit amount of space occupied by an object 52 Chapter 1 | Essential Ideas This OpenStax book is available for free at http://cnx.org/content/col11760/1.9 weight force that gravity exerts on an object Key Equations • density = mass volume • T °C = 5 9 × T °F − 32 • T °F = 9 5 × T °C + 32 • T K = °C + 273.15 • T °C = K − 273.15 Summary 1.1 Chemistry in Context Chemistry deals with the composition, structure, and properties of matter, and the ways by which various forms of matter may be interconverted. Thus, it occupies a central place in the study and practice of science and technology. Chemists use the scientific method to perform experiments, pose hypotheses, and formulate laws and develop theories, so that they can better understand the behavior of the natural world. To do so, they operate in the macroscopic, microscopic, and symbolic domains. Chemists measure, analyze, purify, and synthesize a wide variety of substances that are important to our lives. 1.2 Phases and Classification of Matter Matter is anything that occupies space and has mass. The basic building block of matter is the atom, the smallest unit of an element that can enter into combinations with atoms of the same or other elements. In many substances, atoms are combined into molecules. On earth, matter commonly exists in three states: solids, of fixed shape and volume; liquids, of variable shape but fixed volume; and gases, of variable shape and volume.
eBook - PDF- William R. Robinson, Edward J. Neth, Paul Flowers, Klaus Theopold, Richard Langley(Authors)
- 2016(Publication Date)
- Openstax(Publisher)
has a definite shape, and has a fairly constant volume specialized language used to represent components of the macroscopic and microscopic domains, such as chemical symbols, chemical formulas, chemical equations, graphs, drawings, and calculations well-substantiated, comprehensive, testable explanation of a particular aspect of nature estimate of amount by which measurement differs from true value standard of comparison for measurements ratio of equivalent quantities expressed with different units; used to convert from one unit to a different unit amount of space occupied by an object 52 Chapter 1 | Essential Ideas This OpenStax book is available for free at http://cnx.org/content/col12012/1.7 weight force that gravity exerts on an object Key Equations • density = mass volume • T °C = 5 9 × T °F − 32 • T °F = 9 5 × T °C + 32 • T K = °C + 273.15 • T °C = K − 273.15 Summary 1.1 Chemistry in Context Chemistry deals with the composition, structure, and properties of matter, and the ways by which various forms of matter may be interconverted. Thus, it occupies a central place in the study and practice of science and technology. Chemists use the scientific method to perform experiments, pose hypotheses, and formulate laws and develop theories, so that they can better understand the behavior of the natural world. To do so, they operate in the macroscopic, microscopic, and symbolic domains. Chemists measure, analyze, purify, and synthesize a wide variety of substances that are important to our lives. 1.2 Phases and Classification of Matter Matter is anything that occupies space and has mass. The basic building block of matter is the atom, the smallest unit of an element that can enter into combinations with atoms of the same or other elements. In many substances, atoms are combined into molecules. On earth, matter commonly exists in three states: solids, of fixed shape and volume; liquids, of variable shape but fixed volume; and gases, of variable shape and volume.
eBook - PDF- Morris Hein, Susan Arena, Cary Willard(Authors)
- 2021(Publication Date)
- Wiley(Publisher)
130 CHAPTER 7 Quantitative Composition of Compounds Solitaire/Shutterstock CHAPTER OUTLINE 7.1 The Mole 7.2 Molar Mass of Compounds 7.3 Percent Composition of Compounds 7.4 Calculating Empirical Formulas 7.5 Calculating the Molecular Formula from the Empirical Formula Cereals, cleaning products, and pain remedies all list their ingredients on the package label. The ingredients are listed in order from most to least, but the amounts are rarely given. However, it is precisely these amounts that give products their desired properties and distinguish them from the competition. Understandably, manufacturers carefully regulate the amounts of ingredients to maintain quality and hopefully their custom- ers’ loyalty. The candies in the photo above are made with a sweet center covered in a layer of sucrose or table sugar. They can be measured by counting or weighing. The composition of compounds is an important concept in chemis- try. Determining numerical relationships among the elements in com- pounds and measuring exact quantities of particles are fundamental tasks that chemists routinely perform in their daily work. 7.1 The Mole 131 7.1 The Mole LEARNING OBJECTIVE: Apply the concepts of the mole, molar mass, and Avogadro’s number to solve chemistry problems. The atom is an incredibly tiny object. Its mass is far too small to measure on an ordinary balance. In Chapter 5 (Section 5.6), we learned to compare atoms using a table of atomic mass units. These units are valuable when we compare the masses of individual atoms (mentally), but they have no practical use in the laboratory. The mass in grams for an “average” carbon atom (atomic mass 12.01 u) would be 2.00 × 10 −23 g, which is much too tiny for the best laboratory balance. So how can we confidently measure masses for these very tiny atoms? We increase the number of atoms in a sample until we have an amount large enough to measure on a labora- tory balance.
eBook - PDFChemistry
An Atoms First Approach
- Steven Zumdahl, Susan Zumdahl, Donald J. DeCoste, , Steven Zumdahl, Steven Zumdahl, Susan Zumdahl, Donald J. DeCoste(Authors)
- 2020(Publication Date)
- Cengage Learning EMEA(Publisher)
Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 5.5 Molar Mass A chemical compound is, ultimately, a collection of atoms. For example, methane (the major component of natural gas) consists of molecules that each contain one carbon and four hydrogen atoms (CH 4 ). How can we calculate the mass of 1 mole of methane? That is, what is the mass of 6.022 3 10 23 CH 4 molecules? Since each CH 4 molecule contains one carbon atom and four hydrogen atoms, 1 mole of CH 4 molecules contains 1 mole of carbon atoms and 4 moles of hydrogen atoms. The mass of 1 mole of meth- ane can be found by summing the masses of carbon and hydrogen present: Mass of 1 mol C 5 12.01 g Mass of 4 mol H 5 4 3 1.008 g Mass of 1 mol CH 4 5 16.04 g Because 16.04 g represents the mass of 1 mole of methane molecules, it makes sense to call it the molar mass for methane. Thus the molar mass of a substance is the mass in grams of one mole of the compound. Traditionally, the term molecular weight has been used for this quantity. However, we will use molar mass exclusively in this text. The molar mass of a known substance is obtained by summing the masses of the component atoms as we did for methane. Methane is a molecular compound—its components are molecules. Many substances are ionic—they contain simple ions or polyatomic ions. Examples are NaCl (which con- tains Na 1 and Cl 2 ) and CaCO 3 (which contains Ca 21 and CO 3 22 ). Because ionic com- pounds do not contain molecules, we need a special name for the fundamental unit of these materials. Instead of molecule, we use the term formula unit. Thus CaCO 3 is the formula unit for calcium carbonate, and NaCl is the formula unit for sodium chloride. Calculating Molar Mass I Juglone, a dye known for centuries, is produced from the husks of black walnuts.
- Morris Hein, Scott Pattison, Susan Arena, Leo R. Best(Authors)
- 2014(Publication Date)
- Wiley(Publisher)
7.4 • Calculating Empirical Formulas 121 © Hemis/Alamy C ereals, cleaning products, and pain remedies all list their ingredients on the package label. The ingredients are listed in order from most to least, but the amounts are rarely given. However, it is precisely these amounts that give products their desired properties and distinguish them from the competition. Understandably, manufacturers carefully regulate the amounts of in- gredients to maintain quality and hopefully their customers’ loyalty. In the medicines we purchase, these quantities are especially important for safety reasons—for example, they determine whether a medicine is given to children or is safe only for adults. The composition of compounds is an important concept in chemistry. Determining numerical relationships among the elements in compounds and measuring exact quantities of particles are fun- damental tasks that chemists routinely perform in their daily work. 7.1 The Mole 7.2 Molar Mass of Compounds 7.3 Percent Composition of Compounds 7.4 Calculating Empirical Formulas 7.5 Calculating the Molecular Formula from the Empirical Formula QUANTITATIVE COMPOSITION OF COMPOUNDS C H A P T E R 7 C H A P T E R O U T L I N E These black pearls are made of layers of calcium carbonate. They can be measured by counting or weighing. 122 CHAPTER 7 • Quantitative Composition of Compounds 7.1 THE MOLE Apply the concepts of the mole, molar mass, and Avogadro’s number to solve chemistry problems. The atom is an incredibly tiny object. Its mass is far too small to measure on an ordinary bal- ance. In Chapter 5 (Section 5.6), we learned to compare atoms using a table of atomic mass units. These units are valuable when we compare the masses of individual atoms (mentally), but they have no practical use in the laboratory. The mass in grams for an “average” carbon atom (atomic mass 12.01 amu) would be 2.00 * 10 -23 g, which is much too tiny for the best laboratory balance.
eBook - PDF- Morris Hein, Susan Arena, Cary Willard(Authors)
- 2016(Publication Date)
- Wiley(Publisher)
C ereals, cleaning products, and pain remedies all list their ingredients on the package label. The ingre- dients are listed in order from most to least, but the amounts are rarely given. However, it is precisely these amounts that give products their desired properties and distinguish them from the competition. Understandably, manufacturers carefully regulate the amounts of ingredients to maintain quality and hopefully their customers’ loyalty. The black pearls in the photo above are made of layers of calcium carbonate. They can be measured by counting or weighing. The composition of compounds is an important concept in chemistry. Determining numerical relationships among the elements in compounds and measuring exact quantities of particles are fundamental tasks that chemists routinely perform in their daily work. Quantitative Composition of Compounds C H A P T E R O U T L I N E 7.1 The Mole 7.2 Molar Mass of Compounds 7.3 Percent Composition of Compounds 7.4 Calculating Empirical Formulas 7.5 Calculating the Molecular Formula from the Empirical Formula © Hemis/Alamy 7 124 CHAPTER 7 • Quantitative Composition of Compounds 7.1 The Mole Apply the concepts of the mole, molar mass, and Avogadro’s number to solve chemistry problems. The atom is an incredibly tiny object. Its mass is far too small to measure on an ordinary balance. In Chapter 5 (Section 5.6), we learned to compare atoms using a table of atomic mass units. These units are valuable when we compare the masses of individual atoms (mentally), but they have no practical use in the laboratory. The mass in grams for an “average” carbon atom (atomic mass 12.01 u) would be 2.00 × 10 −23 g, which is much too tiny for the best laboratory balance. So how can we confidently measure masses for these very tiny atoms? We increase the number of atoms in a sample until we have an amount large enough to measure on a laboratory balance. The problem then is how to count our sample of atoms.
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