GENERAL CHEMISTRY
`
`P.
`
`W.
`
`A T K
`
`I N S
`
`Oxjind Univenit;'
`
`SCIENTIFIC
`AMERICAN
`B 0 0 KS Distribu-ted by W. H. Ft·eeman
`
`SENJU EXHIBIT 2072
`LUPIN v. SENJU
`IPR2015-01099
`
`Page 1 of 8
`
`

`
`Cover image by Ken Kmp.
`
`Library of Congress Cataloging-in-Publication Data
`
`Atkins, P. W. (Peter William), 1940-
`General chemistry.
`
`Includes index.
`l. Chemistry.
`I. Title.
`QD31.2.A 75 1989
`540
`ISBN 0-7167-1940-l
`
`88-30580
`
`Copyright© 1989 P. W. Atkins.
`
`No part of this book may be reproduced by any mechan(cid:173)
`ical, photographic, or electronic process, or in any form
`of a photographic recording, nor may it be stored in a
`retrieval system, transmitted, or otherwise copied for
`public or private use, without written permission from
`the publisher.
`
`Printed in the United States of America
`
`Scientific American Books is a subsidiary of Scientific
`American, Inc. Distributed by W. H. Freeman and Com(cid:173)
`pany, 41 Madison Avenue, New York, New York 10010
`:> 4 5 6 7 8 9 0 KP 7 6 5 4 3 2
`
`2
`
`() 8 9
`
`Page 2 of 8
`
`

`
`Therefore,
`
`Molality=
`
`0.150 mol
`78.3 X
`kg CH3C5H5
`
`1.92 mol C5HI)f'kg CH3C 0H 5
`
`EXERCISE Calculate the molality of a solution of toluene in benzene,
`given that the mo.le fraction of toluene is 0.150.
`
`[Answer: 2.26 m]
`
`SOLUBILITY
`
`In this chapter we are focusing on aqueous solutions because they are
`so important, but many of our remarks apply equally to nonaqueous
`solutions. In the following discussion, remember that substances which
`dissolve to give solutions of ions that conduct electricity (e.g., sodium
`chloride and acetic acid) are called electrolytes (Section 2. 7); those giv(cid:173)
`ing solutions that do not conduct electricity because the solute remains
`molecular (e.g., glucose and ethanol) are nonelectrolytes.
`
`11.3 SATUR.6:r10N AND SOLUBILITY
`
`If we add 20 g of sucrose-cane sugar-to 100 mL of water at room
`temperature, all the sucrose dissolves. However, if we add 200 g, most
`dissolves but some does not (Fig. 11.4). When the solvent has dissolved
`all the solute it can and some undissolved solute remains, the solution is
`said to be "saturated."
`
`The definition of solubility. If we could follow a single sucrose molecule
`in a saturated solution, we might find that at some instant it is part of
`the surface layer of a sucrose crystal (Fig. 11.5). Shortly after, the mole(cid:173)
`cule might be found in solution. Still later, it might be buried more
`deeply in a crystal, under many layers of molecules that had settled on
`
`FIG U R E 1 1 . 4 When a little su(cid:173)
`crose is shaken with l 00 mL of
`water, it all dissolves (left). How(cid:173)
`ever, when a large amount (more
`than 200 g) is added, some undis(cid:173)
`solved sucrose remains (right).
`
`400
`
`CHAPTER 11 THE PROPERTIES OF SOLUTIONS
`
`Page 3 of 8
`
`

`
`0
`
`0
`
`0
`
`0
`
`0
`
`0
`
`0
`
`FIGURE 11.5 The solute in a
`saturated solution is in dynamic
`equilibrium with the undissolved
`solute. If we could follow a single
`solute particle (the red circle), we
`would sometimes find it in solu(cid:173)
`tion and sometimes in the solute.
`
`it. There it would remain until it became exposed again and was
`return to the solution. In other words, a saturated solution is
`example of dynamic equilibrium (see Section 10.4), in which a
`process and its reverse occur at equal rates. In this case, the
`continues to dissolve, and it does so at a rate that exactly matches
`of the reverse process, the return of solute from the solution.
`~ ..... , ... -u •u the following definition:
`
`we cannot follow a single molecule in a saturated solution,
`experimentally that the equilibrium is dynamic and not
`we can
`static. One way to do so is to add solid silver iodide, containing some
`iodine-131 in place of the usual iodine-127, to a saturated solution of
`silver iodide. Iodine-131 is radioactive and can be detected with Geiger
`counters and other radioactivity-detection devices. After a time the so(cid:173)
`lution becomes radioactive, but the total mass of dissolved solid re(cid:173)
`mains unchanged. This shows that some I- ions have dissolved and
`others have come out of solution, even though the solution was already
`saturated.
`A saturated solution represents th.e limit of a solute's ability to dis(cid:173)
`solve in a given quantity of solvent. It is therefore a natural measure of
`the solute's "solubility" S:
`
`The solubility of a substance in a solvent is the concentration of the
`saturated solution.
`
`The solubilities of some substances are given in Table 11.3. They de(cid:173)
`pend on the solvent, the temperature, and, for. gases, the pressure.
`
`TABLE 11.3
`
`The solubilities of some substances
`
`Solubility,
`g solute/100 g solvent,
`in water at
`
`Compound
`
`NH3
`NH4N03
`CaC12
`CaF2
`CuS04 · 5H 20
`HCl
`
`MgO
`AgF
`AgCl
`
`0°C
`
`89.5
`118
`
`59.5
`1.7 X 10- 3
`
`31.6
`
`82.3
`6 x w- 4
`182
`7 x w- 5
`
`100°C or as
`specified
`
`Other
`solvents
`
`7.4
`871
`
`159
`
`Organic solvents
`Alcohol, ammonia
`
`Alcohol
`
`203.3
`56.1 at 60°C
`8 x 10-3 at 30°C
`
`205
`2 X 10- 3
`
`Alcohol, benzene
`
`11.3 SATURATION AND SOLUBILITY
`
`401
`
`Page 4 of 8
`
`

`
`FIGURE 1 1 . 6 This Chile saltpe(cid:173)
`ter has survived in the arid region
`where it is mined in Chile because
`there is too little groundwater to
`dissolve it and wash it away.
`
`The dependence of solubility on the solute. Some substances are soluble
`in water, others sparingly (slightly) soluble, and others almost insolu- ·
`ble. We can know which behavior to expect by referring to the "solubil(cid:173)
`ity rules," which were given in Table 3.1. We used the rules in Chapter
`3 to choose reagents for precipitation reactions; they are also of help in
`understanding the behavior of some everyday substances and the
`properties of minerals. Because of the solubility of most nitrates, for
`instance, they are rarely found in mineral deposits, for they are usually
`carried away by the water that trickles through the ground. An excep(cid:173)
`tion is the large deposit of sodium nitrate in the arid coastal region of
`Chile, where groundwater is absent. This "Chile saltpeter" (Fig. 11.6) ·
`was the main source of nitrates for fertilizers and explosives until the
`Haber process for ammonia was developed at the start of this century.
`The low solubility of most phosphates is an advantage for skeletons,
`since bone consists largely of calcium phosphate (much of the rest is the
`protein collagen). However, this insolubility is inconvenient for agricul(cid:173)
`ture, since it means that phosphorus, which is essential to the function
`of biological cells, is slow to circulate through the ecosystem. One of
`chemistry's achievements has been the development of manufacturing
`processes to speed phosphates on their way as fertilizers. The phos(cid:173)
`phates and hydrogen phosphates used for fertilizers are obtained from
`phosphate rocks (Fig. 11.7), principally the apatites-hydroxyapatite,
`Ca5(P04)sOH, and fluorapatite, Ca5(P04):,F-by treating them with
`concentrated sulfuric acid:
`
`3H 3P04 (aq) + 5CaS04(s) + H20(l)
`The phosphate rocks themselves were once alive, for they are the .
`crushed and compressed remains of the skeletons of prehistoric ani(cid:173)
`mals. Calcium hydrogen phosphate (CaHP04 ) is more soluble than
`calcium phosphate and is included in commercial phosphate fertilizers.
`Just as hydrogen phosphates are more soluble than phosphates, so
`are more soluble than
`hydrogen carbonates (bicarbonates, HC0 3
`carbonates. This difference is responsible for the behavior of har-d
`water-, water that contains dissolved calcium and magnesium salts.
`particular, the difference accounts for the deposit of scale inside hot
`pipes and for the formation of a scum with soap in hard water. The
`
`FIG U R E 1 1 • 7 Mining of phos(cid:173)
`phate rock, the crushed remains
`of the skeletons of prehistoric ani(cid:173)
`mals.
`
`402
`
`CHAPTER 11 THE PROPERTIES OF SOLUTIONS
`
`Page 5 of 8
`
`

`
`(a)
`
`(b)
`
`(c)
`
`behavior of hard water begins with the fact that rainwater contains
`dissolved carbon dioxide, and hence some carbonic acid from the reac(cid:173)
`tion
`
`C02(g) + H20(l) ----'T H2C03(aq)
`As the water runs along and through the ground, the carbonic acid
`.reacts with the calcium carbonate of limestone or chalk and forms the
`more soluble hydrogen carbonate:
`CaC03(s) + H2C03(aq) ----'T Ca(HC03)2(aq)
`These reactions are reversed when the water is heated in a kettle or
`furnace:
`
`2HC0g -(aq) ~ C032-(aq) + C02(g) + H20(l)
`The carbon dioxide is driven off, leaving carbonate ions in solution,
`·and the almost insoluble calcium carbonate is deposited as scale.
`
`The dependence of solubility on the solvent. In many instances, the de(cid:173)
`pendence of the solubility of a substance on the identity of the solvent
`can be summarized by the rule that "like dissolves like." That is, a polar
`liquid, such as water, is generally a much better solvent than a nonpolar
`one (such as benzene) for ionic and polar compounds. Conversely,
`nonpolar liquids, including benzene and the tetrachloroethylene
`(C2Cl4 ) used for dry cleaning, are often better solvents for nonpolar
`. compounds than for polar compounds (Fig. 11.8). The reason is that
`the energy of the solute molecules is similar in the solution to what it
`was in the original solid if the intermolecular forces in solution and
`solid are similar.
`If the principal cohesive forces in a solute are hydrogen bonds, the
`"like dissolves like" rule implies that it is more likely to dissolve in a
`hydrogen-bonding solvent than in others. Sucrose, for example, dis(cid:173)
`solves readily in water but not in benzene. Similarly, if the principal
`cohesive forces are London forces, the best solvent is likely to be one
`. held together by the same kind of forces. One example is carbon disul(cid:173)
`fide, which is a far better solvent for sulfur than is water (Fig. 11.9),
`because solid sulfur is a molecular solid of S8 molecules held together
`by London forces.
`
`Soaps and detergents. Modern soaps and detergents are a practical
`application of the principle of like dissolving like. Soaps are the sodium
`salts of organic acids with long hydrocarbon chains, including sodium
`
`FIGURE 1 1 • 8 Like often dis(cid:173)
`solves like. (a) Intermolecular in(cid:173)
`teractions help a polar solvent to
`dissolve other polar substances,
`(b) a hydrogen-bonding solvent to
`dissolve substances held together
`by hydrogen bonds, and (c) a sol(cid:173)
`vent with strong London forces to
`dissolve nonpolar molecular sol(cid:173)
`ids.
`
`FIG U R E 1 1 • 9 The molecular
`solid sulfur does not dissolve in
`water (left) but does dissolve in
`carbon disulfide (right), with
`which its molecules have strongly
`favorable London interactions.
`
`1.3 SATURATION AND SOLUBILITY
`
`403
`
`Page 6 of 8
`
`

`
`stearate (1); we shall denote them NaA, where HA is the organic acid.
`The anions have a polar group (called the "head group") at one end of
`a long nonpolar group, the hydrocarbon chain. The anions (A-) sink
`their nonpolar and thus hydrophobic, or water-repelling, hydrocarbon
`tails into a blob of grease. Their hydrophilic, or water-attracting, head.
`groups remain on the surface of the grease blob, coating it with a skin
`of polar hydrogen-bonding groups (Fig. 1 L 1 0). The polar head
`groups enable the grease blob to dissolve in water and to be washed
`away.
`A problem with soaps is that they form a scum in hard water. The
`scum is the product of a precipitation reaction that occurs because cal(cid:173)
`cium salts are less soluble than sodium salts:
`Ca2+(aq) + 2A -(aq) ~ CaA2(s)
`One way of avoiding the problem is to use another precipitation reac(cid:173)
`tion to remove the Ca2+ ions from the water before the soap is used.
`This can be done by adding sodium carbonate ("washing soda") to the
`water and precipitating calcium carbonate:
`Ca(HC03h(aq) + Na2C03(aq) ~ CaC03(s) + 2NaHC03(aq)
`Another way to avoid soap scum is to add polyphosphate ions to the
`water as a component of the detergent. Polyphosphate ions (2) are
`formed when phosphates are heated, and they consist of chains and·
`rings of P04 groups. The first step in their formation is
`
`0
`0
`0
`0
`II
`II
`II
`II
`HO-P-OH + HO-P-OH ~ HO-P-0-P-OH + H 20
`I
`I
`I
`I
`OH
`OH
`OH OH
`
`t;
`
`Polyphosphate ions are big, and when they are added to hard water,
`they wrap around the calcium cations and hide them away from other·
`anions with which they would normally precipitate. This wrapping up
`of one ion by another is called sequestration of the ion (from the Latin
`word for "hiding away"), and the polyphosphates are called "sequester(cid:173)
`ing agents."
`Modern commercial detergents are mixtures of compounds, the
`most important of which is the "surface-active agent," or "surfactant.''
`Surfactant molecules are synthetic organic compounds that resemble
`the one shown below (3). Like the stearate ion, they have a hydrophilic
`
`1 Sodium stearate
`
`2 Polyphosphate ion
`
`3 A typical surfactant molecule
`
`404
`
`CHAPTER 11 THE PROPERTIES OF SOLUTIONS
`
`Page 7 of 8
`
`

`
`head group and a hydrophobic tail, and they act similarly. Detergents
`also contain polyphosphates to sequester calcium ions and to adjust the
`acidity. Other additives in the mixture "fluoresce" (absorb ultraviolet
`light and then give out visible light) to give the impression of greater
`cleanliness.
`
`11.4 THE EFFECT OF PRESSURE ON GAS SOLUBILITY
`
`We have noted that solubility depends on the pressure the solution
`experiences. The strongest dependence is shown by gases, which are
`more soluble at higher pressures (Fig. 11.11). A practical application of
`this phenomenon is the production of soft drinks and champagne. In
`each case carbon dioxide is dissolved in the liquid under pressure (in
`champagne, as a result of fermentation that continues in the sealed
`bottle). When the bottle is opened the pressure is released, the solubil(cid:173)
`ity of the gas is greatly reduced, and the gas effervesces (bubbles out of
`solution) with a pop. A more serious consequence of the dependence of
`gas solubility on pressure is the additional nitrogen that dissolves in the
`blood of deep-sea divers. The dissolved nitrogen effervesces when the
`diver returns to the surface, resulting in the formation of numerous
`small bubbles in the bloodstream (Fig. 11.12). These bubbles can block
`the capillaries-the narrow vessels that distribute the blood-and
`starve the tissues of oxygen, causing the painful condition known as the
`"bends," which in serious cases can lead to death. The risk of the bends
`is reduced if helium is used instead of nitrogen to dilute the diver's
`oxygen supply, for helium is much less soluble than nitrogen.
`
`Henry's law. The dependence of the solubility of a gas on its pressure
`was summarized in 1801 by the English chemist William Henry:
`
`Henry's law: The solubility of a gas in a liquid is proportional to its
`partial pressure.
`
`.This law is normally written
`
`S = kH X p
`
`where Pis the partial pressure of the gas, and kH, which is called Henry's
`constant. depends on the gas, the solvent, and the temperature (see
`
`(a)
`
`(b)
`
`FIGURE 11 • 1 0 The hydropho(cid:173)
`bic tail of a soap or surfactant
`molecule enters the blob of
`grease, leaving the hydrophilic
`polar head group on the surface.
`
`0.5
`Pressure ( atm)
`
`1.0
`
`F I G U R E 1 1 • 1 1 The variation
`of the solubilities of oxygen, ni(cid:173)
`trogen, and helium with the pres(cid:173)
`sure. Note that the solubility of
`each gas is doubled when the
`pressure is doubled.
`
`FIGURE 11.12 The small bub(cid:173)
`bles of air are responsible for the
`"bends." (a) Normal blood vessels;
`(b) catastrophic collapse as bub(cid:173)
`bles of gas escape from solution
`in the blood plasma.
`
`11.4 THE EFFECT OF PRESSURE ON GAS SOLUBILITY
`
`405
`
`Page 8 of 8