Chemistry
Solutions and Mixtures
Solutions and mixtures are combinations of two or more substances. A solution is a homogeneous mixture where one substance dissolves in another, while a mixture is a combination of substances that are not chemically bonded. Solutions can be solid, liquid, or gas, while mixtures can be homogeneous or heterogeneous. Both solutions and mixtures play important roles in various chemical processes and everyday life.
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7 Key excerpts on "Solutions and Mixtures"
- Frederick Bettelheim, William Brown, Mary Campbell, Shawn Farrell(Authors)
- 2019(Publication Date)
- Cengage Learning EMEA(Publisher)
168 Solutions and Colloids 6 CONTENTS 6.1 Introduction to Mixtures 6.2 The Most Common Types of Solutions 6.3 The Distinguishing Characteristics of Solutions 6.4 Factors Affecting Solubility 6.5 The Most Common Units for Concentration 6.6 Water as a Good Solvent 6.7 Colloids 6.8 Colligative Properties 6.1 Introduction to Mixtures In Chapter 2, we discussed pure substances—compounds made of two or more elements in a fixed ratio. Such systems are the easiest to study, so it was convenient to begin with them. In our daily lives, however, we more fre-quently encounter mixtures—systems consisting of more than one compo-nent. Air, smoke, seawater, milk, blood, and rocks, for example, are mixtures (Section 2.2C). Recall that the molecular level is the aspect at which the interactions be-tween molecules becomes significant. If a mixture is uniform throughout at the molecular level, it is called a homogeneous mixture or, more commonly, a solution. Filtered air and seawater, for example, are both solutions. They are clear and transparent. In contrast, in most rocks we can see distinct re-gions separated from each other by well-defined boundaries. Such rocks are heterogeneous mixtures. Another example is a mixture of sand and sugar. We can easily distinguish between the two components; the mixing does not occur at the molecular level (Figure 2.3). Thus, mixtures are classified on the basis of how they look to the unaided eye. Some systems, however, fall between homogeneous and heterogeneous mixtures. Cigarette smoke, milk, and blood plasma may look homogeneous, but they do not have the transparency of air or seawater. These mixtures are classified as suspensions. We will deal with such systems in Section 6.7. Although mixtures can contain many components, we will generally re-strict our discussion to two-component systems, with the understanding that everything we say can be extended to multicomponent systems.
eBook - PDF- Douglas P. Heller, Carl H. Snyder(Authors)
- 2015(Publication Date)
- Wiley(Publisher)
202 CHAPTER 7 Water and Other Solutions 7. 1 Solutions and Other Mixtures LEARNING OBJECTIVES 1. Identify the basic components of a solution. 2. Describe how water acts as a solvent. 3. Explain how colloids and dispersions differ from solutions. hemists often say there is a bit of something in just about anything else, meaning that the substances we find around us are typically mixtures. It is quite rare to find something that is truly chemical- ly pure. In this section, we explore types of mixtures called solutions and discuss related topics. Types of Solutions If you steep a tea bag in a cup of hot water, components of the tea leaves are extracted into the water to make a solution. Water is the C solvent, and the various flavored compounds, pigments, and caffeine naturally present in the tea leaves are the solutes––the substances that dissolve within the solvent. Sweetening the tea with table sugar adds yet another solute, sucrose, to the solution. Swirling the tea with a spoon ensures that the mixture is homogeneous, having a uniform composition throughout, a property common to all true solutions. The word solution derives from the Latin solutio, meaning a loosening or unfastening, which reflects what appears to happen to a substance as it dissolves in a solvent. But keep in mind that solution formation is a physical process—a change in form of the substances involved. Solution formation does not involve any chemical reactions. We typically think of solutions as liquids, but solutions can also be gases or solids (Fig- ure 7.1).
eBook - PDFChemistry for Today
General, Organic, and Biochemistry
- Spencer Seager, Michael Slabaugh, Maren Hansen, , Spencer Seager, Spencer Seager, Michael Slabaugh, Maren Hansen(Authors)
- 2021(Publication Date)
- Cengage Learning EMEA(Publisher)
(Section 7.3) 4 Calculate solution concentrations in units of molarity, weight/weight percent, weight/volume percent, and volume/ volume percent. (Section 7.4) Elnur/Shutterstock.com Copyright 2022 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. Solutions and Colloids 199 EARLIER, homogeneous matter was classified into two categories—pure substances and mixtures (see Figure 1.8). Since then, the discussion has been limited to pure substances. We now look at homogeneous mixtures called solutions and their distant relatives, colloidal suspensions. Solutions and colloidal suspensions are very important in our world. They bring nutrients to the cells of our bodies and carry away waste products. The ocean is a solution of water, sodium chloride, and many other substances (even gold). Many chemical reactions take place in solution—including most of those discussed in this book. 7.1 Physical States of Solutions Learning Objective 1 Classify mixtures as solutions or nonsolutions based on their appearance. Solutions are homogeneous mixtures of two or more substances in which the components are present as atoms, molecules, or ions. These uniformly distributed particles are too small to reflect light, and as a result liquid solutions are transparent (clear); light passes through them. In addition, some solutions are colored. The component particles are in constant motion (remember the kinetic theory, Section 6.2) and do not settle under the influence of gravity. In most solutions, a larger amount of one substance is present compared to the other components.
- Morris Hein, Scott Pattison, Susan Arena, Leo R. Best(Authors)
- 2014(Publication Date)
- Wiley(Publisher)
Photodisc M ost substances we encounter in our daily lives are mixtures. Often they are homogeneous mixtures, which are called solutions. Some solutions we commonly encounter are shampoo, soft drinks, and wine. Blood plasma is a complex mixture composed of compounds and ions dissolved in water and proteins suspended in the solution. These solutions all have water as a main component, but many common items, such as air, gasoline, and steel, are also solutions that do not contain water. What are the neces- sary components of a solution? Why do some substances dissolve, while others do not? What effect does a dissolved substance have on the properties of the solution? Answering these questions is the first step in understanding the solutions we encounter in our daily lives. 14.1 General Properties of Solutions 14.2 Solubility 14.3 Rate of Dissolving Solids 14.4 Concentration of Solutions 14.5 Colligative Properties of Solutions 14.6 Osmosis and Osmotic Pressure SOLUTIONS C H A P T E R 14 Brass, a solid solution of zinc and copper, is used to make musical instruments and many other objects. C H A P T E R O U T L I N E 306 CHAPTER 14 • Solutions 14.1 GENERAL PROPERTIES OF SOLUTIONS List the properties of a true solution. The term solution is used in chemistry to describe a system in which one or more substances are homogeneously mixed or dissolved in another substance. A simple solution has two com- ponents: a solute and a solvent. The solute is the component that is dissolved or is the least abundant component in the solution. The solvent is the dissolving agent or the most abundant component in the solution. For example, when salt is dissolved in water to form a solution, salt is the solute and water is the solvent. Complex solutions containing more than one solute and/or more than one solvent are common.
eBook - PDFChemistry
The Molecular Nature of Matter
- James E. Brady, Neil D. Jespersen, Alison Hyslop(Authors)
- 2014(Publication Date)
- Wiley(Publisher)
Lawrence Lawry/Photo Researchers Mixtures at the Molecular Level: Properties of Solutions Chapter Outline 12.1 | Intermolecular Forces and the Formation of Solutions 12.2 | Heats of Solution 12.3 | Solubility as a Function of Temperature 12.4 | Henry’s Law 12.5 | Concentration Units 12.6 | Colligative Properties 12.7 | Heterogeneous Mixtures The value of gemstones lies in their beauty and rarity. However, as chemists, we can think of them as solutions: solid solutions with the solute that gives them their colors. Chromium in aluminum oxide for rubies, chromium in beryllium aluminosilicate for emeralds, iron and titanium in aluminum oxide for sapphires, and copper in copper phosphoaluminate for turquoise—these metals are dissolved in the solids. 12 575 576 Chapter 12 | Mixtures at the Molecular Level: Properties of Solutions I n Chapter 4 we discussed solutions as a medium for carrying out chemical reactions. Our focus at that time was on the kinds of reactions that take place in solution, and in particular, those that occur when water is the solvent. In this chapter we will examine how the addition of a solute affects the physical properties of the mixture. In our daily lives we take advantage of many of these effects. For example, we add ethylene glycol (antifreeze) to the water in a car’s radiator to protect it against freezing and overheating because water has a lower freezing point and higher boiling point when solutes are dissolved in it. Here we will study not only aqueous solutions, but also solutions involving other solvents. We will concentrate on liquid solutions, although solutions can also be gaseous or solid. In fact, all gases mix completely at the molecular level, so the gas mixtures we examined in Chapter 10 were gaseous solutions. Solid solutions, called alloys, include such materials as brass and bronze.
eBook - PDFBasic Physical Chemistry
The Route to Understanding
- E Brian Smith(Author)
- 2012(Publication Date)
- ICP(Publisher)
10 Mixtures and Solutions Many chemical experiments are carried out in solution and it is therefore very important that we are able to understand the behaviour of substances in solution. The simplest model of a mixture is the ideal solution . Such a solution is formed when the components have molecular interactions which are virtually identical. It is a severe approximation, but it provides the platform from which all real solutions are approached. 10.1 The ideal solution Consider the process where two very similar, but distinct, substances are mixed. The mixing leads to an increase in entropy which arises because, whereas the interchange of molecules in a pure compound does not produce a different microstate, the exchange of molecules in a mixture does. If we assume the components are sufficiently similar to mix randomly, then W mix = (n 1 + n 2 ) ! n 1 ! n 2 ! (see Section 7.4). However, since S = k ln W and Stirling’s approximation, when N is large, gives ln N ! = N ln N − N , we obtain, for the entropy arising from the mixing process, mix S = k [ (n 1 + n 2 ) ln (n 1 + n 2 ) − (n 1 + n 2 ) − n 1 ln n 1 − n 2 ln n 2 + n 1 + n 2 ] . This can be rearranged to give, mix S = k (n 1 + n 2 ) − n 1 (n 1 + n 2 ) ln n 1 (n 1 + n 2 ) − n 2 (n 1 + n 2 ) ln n 2 (n 1 + n 2 ) . 231 232 | Basic Physical Chemistry The mole fraction of component one is x 1 = n 1 /(n 1 + n 2 , ) , that of component two is x 2 = n 2 /(n 1 + n 2 ) and ( n 1 + n 2 ) = N , so we obtain mix S = − Nk(x 1 ln x 1 + x 2 ln x 2 ) and, for one mole, when N = N A , mix S = − R(x 1 ln x 1 + x 2 ln x 2 ). x i < 1 and so mix S > 1 and the entropy change on mixing is positive. We assume that, since the molecules making up the mixture are very similar, mix H = 0 . And, since mix G = mix H − T mix S , we obtain, for an ideal solution, mix G = RT (x 1 ln x 1 + x 2 ln x 2 ). mix G < 1 and mixing occurs with a negative free energy change and, therefore, is a spontaneous process.
eBook - PDF- David A. Ucko(Author)
- 2013(Publication Date)
- Academic Press(Publisher)
The solubility of most solids in water increases with increasing temperature. 13.4 A solution is saturated when it contains the maximum possible amount of dissolved solute under normal conditions at a particular temperature. At this point, the rate at which solute dissolves exactly equals the rate at which solute returns from the solution. 13.5 Liquids that mix completely in any proportion are said to be miscible. Immiscible liquids do not mix. All gases can mix to form solutions. The solubility of a gas in a liquid increases with increasing pressure but decreases with increasing temperature. 13.6 Solvents serve as a medium in which substances react and form products. Solvents are also used as cleaners, to deposit coatings, and in industrial processing. 13.7 The concentration of a solution describes the amount of solute present in any given quantity of solvent or solution. Concentration can be expressed as a percentage based on the ratios of solute and solution in terms of weight to volume, weight to weight, or volume to volume. 13.8 Molarity is defined as the number of moles of solute per liter of solution. Two solutions with the same molarity contain equal numbers of moles of solute per liter. However, they generally contain different masses of solute. 13.9 Solutions are often prepared by diluting a portion of an existing stock solution. Dilution calculations can be made using the relationship Mi x Vi = M 2 x V 2 , or by using the conversion factor method. 13.10 When a reaction takes place in aqueous solution, some of the reactants and products are often present as ions. The net ionic equation expresses the reaction in simplified form. Spectator ions, those that do not participate in the reaction, do not appear in a net ionic equation. 13.11 Colligative properties are properties that depend only on the number of solute particles in a solution. Colligative properties include 440
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