chemistry: principles and properties
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`
`MICHELL J. SIENKO
`
`Professor of Chemistry
`Cornell University
`
`ROBERT A . PLANE
`
`Professor of Chemistry
`Cornell University
`
`McGRAW-HILL
`
`BOOK COMPANY
`
`New York
`St. Louis
`San Francisco
`Toronto
`
`London
`Sydney
`
`Akermin, Inc.
`Exhibit 1019
`Page 1
`
`

`
`chemistry: principles and properties
`
`Copyright© 1966 by
`McGraw-Hill, Inc.
`All rights reserved.
`Printed in the United States
`of America.
`This book, or parts thereof,
`may not be reproduced
`in any form without
`permission of the publishers.
`Library of Congress Catalog Card Number 65-28366
`57358
`34567890 BK 732106987
`
`Akermin, Inc.
`Exhibit 1019
`Page 2
`
`

`
`8 solutions
`
`1 the same
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`1itial tem-
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`The preceding discussion of the solid, liquid , and gaseous states was
`limited to pure substances. In practice, we continually deal with mix(cid:173)
`tures; hence the question that arises is the effect of mixing in a second
`component. A mixture is classified as heterogeneous or homogeneous.
`By its nature , a heterogeneous mixture consists of distinct phases, and
`the observed properties are largely the sum of those of the individual
`phases . However, a homogeneous mixture consists of a single phase
`which has properties that may differ drastically from those of the indivi(cid:173)
`dual components. These homogeneous mixtures, or solutions, are of
`widespread importance in chemistry and deserve intensive study.
`
`173
`
`Akermin, Inc.
`Exhibit 1019
`Page 3
`
`

`
`8.1 TYPES OF SOLUTIONS
`
`S olutions, defined as homogeneous mixtures of two or more compo(cid:173)
`nents, can be gaseous , liquid, or solid. Gaseous solutions are made by
`dissolving one gas in another. Since all gases mix in all proportions, any
`mi xture of gases is homogeneous and is a solution . The kinetic picture
`of a gaseous solution is like that of a pure gas, except that the mole(cid:173)
`cules are of different kinds. Ideally, the molecules move independently
`of each other.
`Liquid solutions are made by dissolving a gas, liquid , or solid in a
`liquid . If the liquid is water, the solution is called an aqueous solution.
`In the kinetic picture of a sugar-water solution , sugar molecules are
`distributed at random throughout the bulk of the solution . It is evident
`that on this molecular scale the term " homogeneous" has little signifi(cid:173)
`cance . However , experiments cannot be performed with less than bil(cid:173)
`lions of molecules, so for practical purposes the solution is homogeneous.
`Solid solutions are solids in which one component is randomly dis(cid:173)
`persed on an atomic or molecular scale throughout another component.
`As in any crystal, the packing of atoms is orderly, even though there is
`no particular order as to which lattice points are occupied by which
`kind of atom. Solid solutions are of great practical importance, since
`they make up a large fraction of the class of substances known as
`alloys. An alloy may be defined as a combination of two or more ele(cid:173)
`ments which has metallic properties. Sterling silver, for example, is an
`alloy consisting of a solid solution of copper in silver. In brass, an alloy
`of copper and zinc, it is possible to have a solid solution in whicH some
`copper atoms of the face-centered-cubic structure of pure copper have
`been replaced by zinc atoms. Some kinds of steel are alloys of iron and
`carbon and can be considered as solid solutions in which carbon atoms
`are located in some of the spaces between iron atoms. The iron atoms
`are arranged in the regular structure of pure iron . It should be pointed
`out, however, that not all alloys are sol id solutions. Some alloys, such
`as bismuth-cadmium , are heterogeneous mixtures containing tiny crys(cid:173)
`tals of the constituent elements . Others, such as MgCu 2 , are inter(cid:173)
`metallic compounds which contain atoms of different metals combined
`in definite proportions.
`Two terms that are convenient in the discussion of solutions are
`solute and solvent. Accepted procedure is to refer to the substance
`present in larger amount as the solvent and to the substance present
`in smaller amount as the solute. However, the terms can be inter(cid:173)
`changed whenever it is convenient. For example, in speaking of solu(cid:173)
`tions of sulfuric acid and water, sulfuric acid is sometimes referred to
`as the solute and water as the solvent even when the water molecules
`are in the minority.
`
`8.2 Concentration
`174
`
`8.2 CONCENTRATION
`
`The properties of solutions, e.g. , the color of a dye solution or the
`sweetness of a sugar solution, depend on the solution concentration.
`There are several common methods for describing concentration.
`
`Sc
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`Akermin, Inc_
`Exhibit 1019
`Page 4
`
`

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`8.8 COLLOIDS
`
`In introducing the topic of solutions it was more or less implied that it
`is easily possible to distinguish between a homogeneous mixture and a
`heterogeneous mixture. However, this distinction is not a sharp one.
`There are systems which are neither obviously homogeneous nor ob·
`viously heterogeneous. They are classed as intermediate and are known
`as colloids. In order to get an idea of what a colloid is, we imagine a
`process in which a sample of solid is placed in a liquid and subdivided.
`So long as distinct particles of solid are visible to the naked eye, there
`is no question that the system is heterogeneous. On standing, these
`visible particles separate out. Depending on the relative density of the
`solid and the liquid , the solid particles float to the top or settle to the
`bottom . They can be separated easily by filtration. As the solid is
`progressively subdivided , a state in which the dispersed particles have
`been broken down to individual molecules or atoms is eventually
`reached. In this limit, a solution in which two phases can no longer be
`distinguished is produced . No matter how powerful a microscope is
`used, a solution appears uniform throughout, and individual molecules
`cannot be seen. On standing, the dispersed particles do not separate
`out, nor can they be separated by filtration .
`Between coarse suspensions and true solutions there is a region of
`change from heterogeneity to homogeneity. In this region dispersed
`particles are so small that they do not form an obviously separate
`phase, but they are not so small that they can be said to be in true solu·
`tion . This state of subdivision is called the colloidal state. On standing,
`the particles of a colloid do not separate out at any appreciable rate;
`they cannot be seen under a microscope; nor can they be separated by
`filtration. The dividing lines between colloids and solutions and between
`colloids and discrete phases are not rigorously fixed, since a continuous
`gradation of particle size is possible. Usually, however, colloids are de·
`fined as a separate class on the basis of size. When the particle size
`lies between about 10~7 and 10 ~4 em , the dispersion is called a colloid,
`a colloidal suspension, or a colloidal solution.
`The size of a dispersed particle does not tell anything about the con·
`stitution of the particle. The particle may consist of atoms, of small
`molecules, or of one giant molecule sometimes called a macromolecule.
`For example, colloidal gold consists of various-sized particles each con·
`taining a million or more gold atoms. Colloidal sulfur can be made with
`particles containing a thousand or so S8 molecules. An example of a
`macromolecule is hemoglobin, the protein responsible for the red color
`of blood. The molecular mass of this molecule is 66800, and the diam·
`eter is approximately 3 x 10 ~ 7 em.
`Colloids are frequently classified on the basis of the states of aggre·
`gation of the component phases, even though the separate phases are
`not visibly distinguishable once the colloid is formed. The more impor·
`tant classifications are sols, emulsions, gels, and aerosols. In sols a
`solid is dispersed through a liqu id, so that the liquid forms the contin·
`uous phase and bits of solid form the discontinuous phase. Milk of
`
`I
`
`8.8 Colloids
`192
`
`Lig
`sour
`
`8 .13
`Light scattering
`
`Akermin, Inc.
`Exhibit 1019
`Page 5
`
`

`
`!d that it
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`:les have
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`
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`ispersed
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`rue solu(cid:173)
`tand ing,
`ble rate;
`rated by
`between
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`; are de(cid:173)
`icle size
`1 colloid,
`
`the con(cid:173)
`of small
`1olecule.
`ach con(cid:173)
`ad e with
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`
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`Milk of
`
`Light
`source
`
`8.13
`Light scattering
`
`Colloid
`
`)
`
`magnesia is a sol consisting of solid particles of magnesium hydroxide
`dispersed through water. Sols can be made by breaking down large par(cid:173)
`ticles or building up small particles to colloidal dimensions. Colloidal
`gold can be made by striking an electric arc between two gold electrodes
`under water. It can also be made by the chemical reduction of chlorauric
`acid, HAuC1 4 , by a slow reducing agent such as hydrazine, N2 H4 . In(cid:173)
`vestigation of gold sol by X rays has shown that the particles of gold
`which are dispersed throughout the water are crystalline in nature.
`Emulsions are colloids in which a liquid is dispersed through a
`liqu id. A common example is ordinary milk, which consists of butterfat
`globules dispersed through an aqueous solution. A gel is an unusual
`type of colloid in which a liquid contains a solid arranged in a fine net(cid:173)
`work extending throughout the system. Both the solid and the liquid
`phases are continuous. Examples of gels are jellies, gelatin, agar, and
`slimy precipitates such as aluminum hydroxide. An aerosol is a colloid
`made by dispersing either a solid or a liquid in a gas. The former is
`called a smoke and the latter a fog.
`
`8. 9 LIGHT SCATTERING
`
`When a beam of light is passed through a solution or a pure liquid , the
`path of the beam is not visible from the side. The dissolved particles
`are too small to scatter much light In a colloid the particles are big
`enough to scatter the light Therefore, when a beam of light is turned
`on a colloid, an obse rver to one side can see the path of the beam. The
`situation is shown in Figure 8.13. This effect, ca lled the Tyndall effect,
`can be produced readily by turning a co lumn of light on an aqueous
`solution of sodium thiosulfate, Na 2S20 3 , and adding a few drops of dilute
`acid. The ensuing chemical reaction produces elemental sulfur. The
`light beam is invisible until the sulfur particles aggregate to colloidal
`- dimensions.
`By taking into consideration the wave nature of light, information
`can be obtained from the Tyndall effect about the size and shape of
`the scattering particles. In an ordinary solution the particles of solute
`are much smaller than the wavelength of the light. Visible light has a
`wavelength ranging from 4000 to 7200 A, or from 4.0 x lQ-5 to
`7.2 x lQ - 5 em. Solute particles that are 5 A or so in diameter are too
`small to affect a wave of such length . However, when solute particles
`are of the order of several thousand angstrom units in diameter, the
`light beam is scattered or diffracted and becomes visible from the side.
`
`Solutions
`193
`
`Akermin, Inc.
`Exhibit 1019
`Page 6
`
`

`
`+
`
`8.14
`Electrophoresis
`
`Careful studies of this scattering have been used to determine the size
`of macromolecules.
`When a microscope is focused on a Tyndall beam, light is reflected
`up into the microscope. Although the colloidal particle itself is too small
`to be seen, its position may be fixed by noting where the light appears.
`When observed in this way, colloid al particles are seen to undergo
`Brownian motion, the rapid, random, zigzag motion previously men·
`tioned in discussing gases (Section 5.10). The smaller the particle size,
`the more violent the Brownian motion .
`Under ordinary circumstances, it is observed that a colloid in an un·
`insulated container does not settle out. However, when the colloid is
`kept in a well·insulated container, after a time there will be a gradation
`in the concentration of colloidal particles from the top to the bottom of
`the sample. This gradation in concentration develops because there are
`two opposing effects: (1) the attraction due to gravity, which tends to
`pull heavier particles down, and (2) the dispersing effect due to Brown·
`ian motion. The more massive the particles, the more important is
`effect 1 and the more pronounced is the concentration gradation.* The
`main reason no appreciable concentration gradient is observed for
`colloids in uninsulated containers is that there are convection currents
`due to nonuniform temperature. These currents keep the colloidal
`suspension constantly stirred up.
`
`8.10 ADSORPTION
`
`In some colloids the particles adsorb electric charge. For example,
`ferric oxide sol consists of positively charged aggregates of ferric oxide
`units. The positive charge enhances the stability of the colloid . Nor·
`mally, when one particle in its Brownian motion hits another, the two
`coagulate to form a larger particle. A particle that results from collisions
`between large particles may be so large that Brownian motion cannot
`keep it in suspension . However, ferric oxide has great adsorption power
`for H+. Presumably the H+ ions are stuck on oxygen atoms which
`protrude from the particles. A particle which has H+ adsorbed on it has
`a net positive charge and thereby repels any similarly charged particle.
`The charged ferric oxide particles try to stay as far apart from each
`other on the average as possible. There is little chance that they will
`come together to form a large mass which settles out. Arsenious sui·
`fide, As2S3 , forms a negative sol by adsorbing SH - or OH - ions. It is
`not surprising that mixing a positively charged ferric oxide sol with a
`negatively charged arsenious sulfide sol coagulates them both.
`That some colloidal particles are electrically charged can be shown
`by studying electrophoresis, the migration of colloidal particles in an
`electric field. Figure 8.14 shows the experimental setup. A U tube is
`
`8.10 Adsorption
`194
`
`*Two extreme cases can be imagined. In that of rocks in water the settling is so pronounced
`that all the rocks are at the bottom. In that of a true solution , such as sugar in water, the
`gradation in concentration is so slight that only the most careful experiments involving very
`tall columns and precise temperature control could show any difference in concentration
`between the top and bottom of the sample.
`
`Solutiol
`19
`
`Akermin, Inc.
`Exhibit 1019
`Page 7