CHAPTER FOURTEEN ACIDS AND BASES - Weebly
CHAPTER FOURTEENACIDS AND BASESFor Review1.a. Arrhenius acid: produce H in waterb. B rnsted-Lowry acid: proton (H ) donorc. Lewis acid: electron pair acceptorThe Lewis definition is most general. The Lewis definition can apply to all Arrhenius andBr nsted-Lowry acids; H has an empty 1s orbital and forms bonds to all bases by accepting apair of electrons from the base. In addition, the Lewis definition incorporates other reactions nottypically considered acid-base reactions, e.g., BF3(g) NH3(g) F3B NH3(s). NH3 issomething we usually consider a base and it is a base in this reaction using the Lewis definition;NH3 donates a pair of electrons to form the N B bond.2.a. The Ka reaction always refers to an acid reacting with water to produce the conjugate base ofthe acid and the hydronium ion (H3O ). For a general weak acid HA, the Ka reaction is:HA(aq) H2O(l) A (aq) H3O (aq) where A conjugate base of the acid HAThis reaction is often abbreviated as: HA(aq) H (aq) A (aq)b. The Ka equilibrium constant is the equilibrium constant for the Ka reaction of some substance. For the general Ka reaction, the Ka expression is:Ka [A ][ H3O ][H ][ A ]or K a [HA][HA](for the abbreviated Ka reaction)c. The Kb reaction alwlays refers to a base reacting with water to produce the conjugate acidof the base and the hydroxide ion (OH ). For a general base, B, the Kb reaction is:B(aq) H2O(l) BH (aq) OH (aq) where BH conjugate acid of the base Bd. The Kb equilibrium constant for the general Kb reaction is: Kb [BH ][ OH ][B]e. A conjugate acid-base pair consists of two substances related to each other by the donatingand accepting of a single proton. The conjugate bases of the acids HCl, HNO2, HC2H3O2 andH2SO4 are Cl , NO2 , C2H3O2 , and HSO4 , respectively. The conjugate acids of the basesNH3, C5H5N, and HONH2 are NH4 , C5H5NH , and HONH3 , respectively. Conjugate acidbase pairs only differ by H in their respective formulas.485
4863.CHAPTER 14ACIDS AND BASESa. Amphoteric: a substance that can behave either as an acid or as a base.b. The Kw reaction is also called the autoionization of water reaction. The reaction alwaysoccurs when water is present as the solvent. The reaction is:H2O(l) H2O(l) H3O (aq) OH (aq) or H2O(l) H (aq) OH (aq)c. The Kw equilibrium constant is also called the ion-product constant or the dissociationconstant of water. It is the equilibrium constant for the autoionization reaction of water:Kw [H3O ][OH ] or Kw [H ][OH ]At typical solution temperatures of 25 C, Kw 1.0 10 14.d. pH is a mathematical term which is equal to the –log of the H concentration of a solution(pH –log[H ].e. pOH is a mathematical terem which is equal to the –log of the OH concentration of asolution (pOH –log[OH ]).f.The p of any quantity is the –log of that quantity. So: pKw –logKw. At 25 C, pKw –log(1.0 10 14 ) 14.00.Neutral solution at 25 C: Kw 1.0 10 14 [H ][OH ] and pH pOH 14.00[H ] [OH ] 1.0 10 7 M; pH pOH –log(1.0 10 7 ) 7.00Acidic solution at 25 C:[H ] [OH ]; [H ] 1.0 10 7 M; [OH ] 1.0 10 7 M; pH 7.00; pOH 7.00Basic solution at 25 C:[OH ] [H ]; [OH ] 1.0 10 7 M; [H ] 1.0 10 7 M; pOH 7.00; pH 7.00As a solution becomes more acidic, [H ] increases, so [OH ] decreases, pH decreases, andpOH increases. As a solution becomes more basic, [OH ] increases, so [H ] decreases, pHincreases, and pOH decreases.4.The Ka value refers to the reaction of an acid reacting with water to produce the conjugate baseand H3O . The stronger the acid, the more conjugate base and H3O produced, and the larger theKa value.Strong acids are basically 100% dissociated in water. Therefore, the strong acids have a Ka 1because the equilibrium position lies far to the right. The conjugate bases of strong acids are terrible bases; much worse than water, so we can ignore their basic properties in water.
CHAPTER 14ACIDS AND BASES487Weak acids are only partially dissociated in water. We say that the equilibrium lies far to the left,thus giving values for Ka 1. (We have mostly reactants at equilibrium and few productspresent). The conjugate bases of weak acids are better bases than water. When we have a solutioncomposed of just the conjugate base of a weak acid in water, tbe resulting pH is indeed basic (pH 7.0). In general, as the acid strength increases, the conjugate base strength decreases, or as acidstrength decreases, the conjugate base strength increases. They are inversely related.Base strength is directly related to the Kb value. The larger the Kb value, the more OH producedfrom the Kb reaction, and the more basic the solution (the higher the pH). Weak bases have a Kb 1 and their conjugate acids behave as weak acids in solution. As the strength of the baseincreases, the strength of the conjugate acid gets weaker; the stronger the base, the weaker theconjugate acid, or the weaker the base, the stronger the conjugate acid.5.Strong acids are assumed 100% dissociated in water, and we assume that the amount of H donated by water is negligible. Hence, the equilibrium [H ] of a strong acid is generally equal tothe initial acid concentration ([HA]0). Note that solutions of H2SO4 can be different from this asH2SO4 is a diprotic acid. Also, when you have very dilute solutions of a strong acid, the H contribution from water by itself must be considered. The strong acids to memorize are HCl, HBr,HI, HNO3, HClO4, and H2SO4.Ka values for weak acids are listed in Table 14.2 and in Appendix 5 of the text. Because weakacids only partially dissociate in water, we must solve an equilibrium problem to determine howmuch H is added to water by the weak acid. We write down the Ka reaction, set-up the ICE table,then solve the equilibrium problem. The two assumptions generally made are that acids are lessthan 5% dissociated in water and that the H contribution from water is negligible.The 5% rule comes from the assumptions that weak acids are less than 5% dissociated. When thisis true, the mathematics of the problem are made much easier. The equilibrium expression we getfor weak acids in water generally has the form (assuming an initial acid concentration of 0.10 M):x2x2Ka 0.10 x 0.10The 5% rule refers to assuming 0.10 – x 0.10. The assumption is valid if x is less than 5% of thenumber the assumption was made against ([HA]0). When the 5% rule is valid, solving for x isvery straight forward. When the 5% rule fails, we must solve the mathematical expression exactlyusing the quadratic equation (or your graphing calculator). Even if you do have a graphingcalculator, reference Appendix A1.4 to review the quadratic equation. Appendix A1.4 alsodiscusses the method of successive approximations which can also be used to solve quadratic(and cubic) equations.6.Strong bases are soluble ionic compounds containing the OH anion. Strong bases increase theOH concentration in water by just dissolving. Thus, for strong bases like LiOH, NaOH, KOH,RbOH, and CsOH, the initial concentration of the strong base equals the equilibrium [OH ] ofwater.The other strong bases to memorize have 2 charged metal cations. The soluble ones to know areCa(OH)2, Sr(OH)2, and Ba(OH)2. These are slightly more difficult to solve because they donate 2moles OH for every mole of salt dissolved. Here, the [OH ] is equal to two times the initialconcentration of the soluble alkaline earth hydroxide salt dissolved.
488CHAPTER 14ACIDS AND BASESNeutrally charged organic compounds containing at least one nitrogen atom generally behave asweak bases. The nitrogen atom has an unshared pair of electrons around it. This lone pair ofelectrons is used to form a bond to H .Weak bases only partially react with water to produce OH . To determine the amount of OH produced by the weak acid (and, in turn, the pH of the solution), we set-up the ICE table using theKb reaction of the weak base. The typical weak base equilibrium expression is:Kb x2x2 0.25 x0.25(assuming [B]0 0.25 M)Solving for x gives us the [OH ] in solution. We generally assume that weak bases are only 5%reacted with water and that the OH contribution from water is negligible. The 5% assumptionmakes the math easier. By assuming an expression like 0.25 M – x 0.25 M, the calculation isvery straight forward. The 5% rule applied here is that if (x/0.25) 100 is less than 5%, theassumption is valid. When the assumption is not valid, then we solve the equilibrium expressionexactly using the quadratic equation (or by the method of successive approximations).7.Monoprotic acid: an acid with one acidic proton; the general formula for monoprotic acids isHA.Diprotic acid: an acid with two acidic protons (H2A)Triprotic acid: an acid with three acidic protons (H3A)H2SO4(aq) HSO4 (aq) H (aq)HSO4 (aq) SO42 (aq) H (aq)K a1 1; this is a strong acid.K a 2 0.012; this is a weak acid.When H2SO4 is dissolved in water, the first proton is assumed 100% dissociated because H2SO4 isa strong acid. After H2SO4 dissociates, we have H and HSO4 present. HSO4 is a weak acid andcan donate some more protons to water. To determine the amount of H donated by HSO4 , onemust solve an equilibrium problem using the K a 2 reaction for HSO4 . H (aq) H2PO4 (aq)K a1 7.5 10 3H2PO4 (aq) H (aq) HPO42 (aq)K a 2 6.2 10 8HPO42 (aq) H (aq) PO43 (aq)K a 3 4.8 10 13H3PO4(aq)When H3PO4 is added to water, the three acids that are present are H3PO4, H2PO4 , and HPO42 .H3PO4, with the largest Ka value, is the strongest of these weak acids. The conjugate bases of thethree acids are H2PO4 , HPO42 , and PO43 . Because HPO42 is the weakest acid (smallest Kavalue), its conjugate base (PO43 ) will have the largest Kb value and is the strongest base.
CHAPTER 14ACIDS AND BASES489See Sample Exercises 14.15-14.17 on the strategies used to solve for the pH of polyprotic acids.The strategy to solve most polyprotic acid solutions is covered in Sample Exercise 14.15. Fortypical polyprotic acids, K a1 K a 2 (and K a 3 if a triprotic acid). Because of this, the dominantproducer of H in solution is just the K a1 reaction. We set-up the equilibrium problem using theK a1 reaction and solve for H . We then assume that the H donated by the K a 2 (and K a 3 iftriprotic) reaction is negligible that is, the H donated by the K a1 reaction is assumed to be the H donated by the entire acid system. This assumption is great when K a1 K a 2 (roughly a 1000 folddifference in magnitude).Sample Exercises 14.16 and 14.17 cover strategies for the other type of polyprotic acid problems.This other type is solutions of H2SO4. As discussed above, H2SO4 problems are both a strong acidand a weak acid problem in one. To solve for the [H ], we sometimes must worry about the H contribution from HSO4. Sample Exercise 13.16 is an example of an H2SO4 solution where theHSO4 contribution of H can be ignored. Sample Exercise 14.17 illustrates an H2SO4 problemwhere we can’t ignore the H contribution from HSO4 .8.a. H2O and CH3CO2 b. An acid-base reaction can be thought of as a competiton between two opposing bases. Sincethis equilibrium lies far to the left (Ka 1), CH3CO2 is a stronger base than H2O.c. The acetate ion is a better base than water and produces basic solutions in water. When weput acetate ion into solution as the only major basic species, the reaction is:CH3CO2 H2O CH3CO2H OH Now the competition is between CH3CO2 and OH for the proton. Hydroxide ion is thestrongest base possible in water. The equilibrium above lies far to the left, resulting in a K bvalue less than one. Those species we specifically call weak bases ( 10 14 Kb 1) liebetween H2O and OH in base strength. Weak bases are stronger bases than water but areweaker bases than OH .The NH4 ion is a weak acid because it lies between H2O and H3O (H ) in terms of acidstrength. Weak acids are better acids than water, thus their aqueous solutions are acidic. Theyare weak acids because they are not as strong as H3O (H ). Weak acids only partiallydissociate in water and have Ka values between 10 14 and 1.For a strong acid HX having Ka 1 106, the conjugate base, X , has Kb Kw/Ka 1.0 10 14 / 1 106 1 10 20 .The conjugate bases of strong acids have extremely small values for Kb; so small that they areworse bases than water (Kb Kw). Therefore, conjugate bases of strong acids have no basicproperties in water. They are present, but they only balance charge in solution and nothing else.The conjugate bases of the six strong acids are Cl , Br , I , NO3 , ClO4 , and HSO4 .
490CHAPTER 14ACIDS AND BASESSummarizing the acid-base properlties of conjugates:a. The conjugate base of a weak acid is a weak base ( 10 14 Kb 1)b. The conjugate acid of a weak base is a weak acid ( 10 14 Ka 1)c. The conjugate base of a strong acid is a worthless base (Kb 10 14 )d. The conjugate acid of a strong base is a worthless acid (Ka 10 14 )Identifying/recognizing the acid-base properties of conjugates is crucial in order to understand theacid-base properties of salts. The salts we will give you will be salts containing the conjugatesdiscussed above. Your job is to recognize the type of conjugate present, and then use thatinformation to solve an equilibrium problem.9.A salt is an ionic compound composed of a cation and an anion.Weak base anions: these are the conjugate bases of the weak acids having the HA generalformula. Table 14.2 lists several HA type acids. Some weak base anions derived from the acids inTable 14.2 are ClO2 , F , NO2 , C2H3O2 , OCl , and CN .Garbage anions (those anions with no basic or acidic properties): these are the conjugate bases ofthe strong acids having the HA general formula. Some neutral anions are Cl , NO3 , Br , I , andClO4 .Weak acid cations: these are the conjugate acids of the weak bases which contain nitrogen. Table14.3 lists several nitrogen-containing bases. Some weak acid cations derived from the weak basesin Table 14.3 are NH4 , CH3NH3 , C2H5NH3 , C6H5NH3 , and C5H5NH .Garbage cations (those cations with no acidic properties or basic properties): the most commonones used are the cations in the strong bases. These are Li , Na , K , Rb , Cs , Ca2 , Sr2 , andBa2 .We mix and match the cations and anions to get what type of salt we want. For a weak base salt,we combine a weak base anion with a garbage cation. Some weak base salts are NaF, KNO2,Ca(CN)2, and RbC2H3O2. To determine the pH of a weak base salt, we write out the Kb reactionfor the weak base anion and determine Kb ( Kw/Ka). We set-up the ICE table under the Kbreaction, and then solve the equilibrium problem to calculate [OH ] and, in turn, pH.For a weak acid salt, we combine a weak acid cation with a garbage anion. Some weak acid saltsare NH4Cl, C5H5NHNO3, CH3NH3I, and C2H5NH3ClO4. To determine the pH, we write out the Kareaction for the weak acid cation and determine Ka ( Kw/Kb). We set-up the ICE table under theKa reaction, and then solve the equilibrium problem to calculate [H ] and, in turn, pH.For a neutral (pH 7.0) salt, we combine a garbage cation with a garbage anion. Some examplesare NaCl, KNO3, BaBr2, and Sr(ClO4)2.
CHAPTER 14ACIDS AND BASES491For salts that contain a weak acid cation and a weak base anion, we compare the K a value of theweak acid cation to the Kb value for the weak base anion. When Ka Kb, the salt produces anacidic solution (pH 7.0). When Kb Ka, the salt produces a basic solution. And when Ka Kb,the salt produces a neutral solution (pH 7.0).10.a. The weaker the X H bond in an oxyacid, the stronger the acid.b. As the electronegativity of neighboring atoms increases in an oxyacid, the strength of the acidincreases.c. As the number of oxygen atoms increases in an oxyacid, the strength of the acid increases.In general, the weaker the acid, the stronger the conjugate base and vice versa.a. Because acid strength increases as the X H bond strength decreases, conjugate base strengthwill increase as the strength of the X H bond increases.b. Because acid strength increases as the electronegativity of neighboring atoms increases,conjugate base strength will decrease as the electronegativity of neighboring atoms increases.c. Because acid strength increases as the number of oxygen atoms increases, conjugate basestrength decreases as the number of oxygen atoms increases.Nonmetal oxides form acidic solutions when dissolved in water:SO3(g) H2O(l) H2SO4(aq)Metal oxides form basic solutions when dissolved in water:CaO(s) H2O(l) Ca(OH)2Questions16.When a strong acid (HX) is added to water, the reaction HX H2O H3O X basically goesto completion. All strong acids in water are completely converted into H3O and X . Thus, noacid stronger than H3O will remain undissociated in water. Similarly, when a strong base (B) isadded to water, the reaction B H2O BH OH basically goes to completion. All basesstronger than OH- are completely converted into OH- and BH . Even though there are acids andbases stronger than H3O and OH , in water these acids and bases are completely converted intoH3O and OH .17.10.78 (4 S.F.); 6.78 (3 S.F.); 0.78 (2 S.F.); A pH value is a logarithm. The numbers to the left ofthe decimal point identify the power of ten to which [H ] is expressed in scientific notation, e.g.,10 11 , 10 7 , 10 1 . The number of decimal places in a pH value identifies the number ofsignificant figures in [H ]. In all three pH values, the [H ] should be expressed only to twosignificant figures because these pH values have only two decimal places.18.A Lewis acid must have an empty orbital to accept an electron pair, and a Lewis base must havean unshared pair of electrons.
49219.CHAPTER 14ACIDS AND BASESa. These are strong acids like HCl, HBr, HI, HNO3, H2SO4 or HClO4.b. These are salts of the conjugate acids of the bases in Table 14.3. These conjugate acids are allweak acids. NH4Cl, CH3NH3NO3, and C2H5NH3Br are three examples. Note that the anionsused to form these salts (Cl , NO3 , and Br ) are conjugate bases of strong acids; this isbecause they have no acidic or basic properties in water (with the exception of HSO4 , whichhas weak acid properties).c. These are strong bases like LiOH, NaOH, KOH, RbOH, CsOH, Ca(OH)2, Sr(OH)2, andBa(OH)2.d. These are salts of the conjugate bases of the neutrally charged weak acids in Table 14.2. Theconjugate bases of weak acids are weak bases themselves. Three examples are NaClO 2,KC2H3O2, and CaF2. The cations used to form these salts are Li , Na , K , Rb, Cs , Ca2 , Sr2 ,and Ba2 since these cations have no acidic or basic properties in water. Notice that these arethe cations of the strong bases you should memorize.e. There are two ways to make a neutral salt. The easiest way is to combine a conjugate base ofa strong acid (except for HSO4 ) with one of the cations from a strong base. These ions haveno acidic/basic properties in water so salts of these ions are neutral. Three examples are NaCl,KNO3, and SrI2. Another type of strong electrolyte that can produce neutral solutions are saltsthat contain an ion with weak acid properties combined with an ion of opposite charge havingweak base properties. If the Ka for the weak acid ion is equal to the Kb for the weak base ion,then the salt will produce a neutral solution. The most common example of this type of salt isammonium acetate, NH4C2H3O2. For this salt, Ka for NH4 Kb for C2H3O2 5.6 10 10 .This salt at any concentration produces a neutral solution.20.Ka Kb Kw, log (Ka Kb) log Kw log Ka log Kb log Kw, pKa pKb pKw 14.00 (at 25 C)21.a. H2O(l) H2O(l) H3O (aq) OH (aq) orH2O(l) H (aq) OH (aq)K Kw [H ][OH ]b. HF(aq) H2O(l) F (aq) H3O (aq) orHF(aq) H (aq) F (aq)c. C5H5N(aq) H2O(l)22.K Ka [H ][ F ][HF] C5H5NH (aq) OH (aq)K Kb [C5 H 5 NH ][ OH ][C 5 H 5 N ]Only statement a is true (assuming the species is not amphoteric). You cannot add a base to waterand get an acidic pH (pH 7.0). For statement b, you can have negative pH values. This justindicates an [H ] 1.0 M. For statement c, a dilute solution of a strong acid can have a higher pHthan a more concentrated weak acid solution. For statement d, the Ba(OH) 2 solution will have an
CHAPTER 1423.ACIDS AND BASES493[OH ] twice of the same concentration of KOH, but this does not correspond to a pOH valuetwice that of the same concentration of KOH (prove it to yourselves).a. This expression holds true for solutions of strong acids having a concentration greater than1.0 10 6 M. 0.10 M HCl, 7.8 M HNO3, and 3.6 10 4 M HClO4 are examples where thisexpression holds true.b. This expression holds true for solutions of weak acids where the two normal assumptionshold. The two assumptions are that water does not contribute enough H to solution to matterand that the acid is less than 5% dissociated in water (from the assumption that x is smallcompared to some number). This expression will generally hold true for solutions of weakacids having a Ka value less than 1 10 4 , as long as there is a significant amount of weakacid present. Three example solutions are 1.5 M HC2H3O2, 0.10 M HOCl, and 0.72 M HCN.c. This expression holds true for strong bases that donate 2 OH ions per formula unit. As longas the concentration of the base is above 5 10 7 M, this expression will hold true. Threeexamples are 5.0 10 3 M Ca(OH)2, 2.1 10 4 M Sr(OH)2, and 9.1 10 5 M Ba(OH)2.d. This expression holds true for solutions of weak bases where the two normal assumptionshold. The assumptions are that the OH contribution from water is negligible and that and thatthe base is less than 5% ionized in water (for the 5% rule to hold). For the 5% rule to hold,you generally need bases with Kb 1 10 4 and concentrations of weak base greater than0.10 M. Three examples are 0.10 M NH3, 0.54 M C6H5NH2, and 1.1 M C5H5N.24.H2CO3 is a weak acid with K a1 4.3 10 7 and K a 2 5.6 10 11 . The [H ] concentration insolution will be determined from the K a1 reaction since K a1 K a 2 . Since K a1 1, then the[H ] 0.10 M; only a small percentage of H2CO3 will dissociate into HCO3 and H . So statement a best describes the 0.10 M H2CO3 solution. H2SO4 is a strong acid and a very good weakacid ( K a1 1, K a 2 1.2 10 2 ). All of the 0.1 M H2SO4 solution will dissociate into 0.10 MH and 0.10 M HSO4 . However, since HSO4 is a good weak acid due to the relatively large Kavalue, then some of the 0.10 M HSO4 will dissociate into some more H and SO42 . Therefore,the [H ] will be greater than 0.10 M, but will not reach 0.20 since only some of 0.10 M HSO4 will dissociate. Statement c is best for a 0.10 M H2SO4 solution.25.One reason HF is a weak acid is that the H F bond is unusually strong and is difficult to break.This contributes significantly to the reluctance of the HF molecules to dissociate in water.26.a. Sulfur reacts with oxygen to produce SO2 and SO3. These sulfur oxides both react with waterto produce H2SO3 and H2SO4, respectively. Acid rain can result when sulfur emissions are notcontrolled. Note that in general, nonmetal oxides react with water to produce acidic solutions.b. CaO reacts with water to produce Ca(OH)2, a strong base. A gardener mixes lime (CaO) intosoil in order to raise the pH of the soil. The effect of adding lime is to add Ca(OH)2. Note thatin general, metal oxides react with water to produce basic solutions.
494CHAPTER 14ACIDS AND BASESExercisesNature of Acids and Bases27.a. HClO4(aq) H2O(l) H3O (aq) ClO4 (aq). Only the forward reaction is indicated sinceHClO4 is a strong acid and is basically 100% dissociated in water. For acids, the dissociationreaction is commonly written without water as a reactant. The common abbreviation for thisreaction is: HClO4(aq) H (aq) ClO4 (aq). This reaction is also called the Ka reaction asthe equilibrium constant for this reaction is called Ka.b. Propanoic acid is a weak acid, so it is only partially dissociated in water. The dissociationreaction is: CH3CH2CO2H(aq) H2O(l) H3O (aq) CH3CH2CO2 (aq) orCH3CH2CO2H(aq) H (aq) CH3CH2CO (aq).c. NH4 is a weak acid. Similar to propanoic acid, the dissociation reaction is:NH4 (aq) H2O(l) H3O (aq) NH3(aq) or NH4 (aq) H (aq) NH3(aq)28.29.The dissociation reaction (the Ka reaction) of an acid in water commonly omits water as areactant. We will follow this practice. All dissociation reactions produce H and the conjugatebase of the acid that is dissociated.[H ][ CN ]a. HCN(aq) H (aq) CN (aq)Ka [HCN ]b. C6H5OH(aq) H (aq) C6H5O (aq)Ka [H ][ C 6 H 5O ][C 6 H 5OH ]c. C6H5NH3 (aq) H (aq) C6H5NH2(aq)Ka [H ][ C 6 H 5 NH 2 ][C 6 H 5 NH 3 ]An acid is a proton (H ) donor and a base is a proton acceptor. A conjugate acid-base pair differsby only a proton (H ).a.b.c.AcidBaseH2CO3C5H5NH C5H5NH H2OH2OHCO3 AcidBaseAl(H2O)63 HONH3 HOClH2OH2OC6H5NH230.a.b.c.ConjugateBase of AcidHCO3 C5H5NC5H5NConjugateBase of AcidAl(H2O)5(OH)2 HONH2OCl-ConjugateAcid of BaseH3O H3O H2CO3ConjugateAcid of BaseH3O H3O C6H5NH3
CHAPTER 1431.ACIDS AND BASES495Strong acids have a Ka 1 and weak acids have Ka 1. Table 14.2 in the text lists some Kavalues for weak acids. Ka values for strong acids are hard to determine so they are not listed in thetext. However, there are only a few common strong acids so if you memorize the strong acids,then all other acids will be weak acids. The strong acids to memorize are HCl, HBr, HI, HNO3,HClO4 and H2SO4.a. HClO4 is a strong acid.b. HOCl is a weak acid (Ka 3.5 10 8 ).c. H2SO4 is a strong acid.d. H2SO3 is a weak diprotic acid with Ka1 and Ka2 values less than one.32.The beaker on the left represents a strong acid in solution; the acid, HA, is 100% dissociated intothe H and A ions. The beaker on the right represents a weak acid in solution; only a little bit ofthe acid, HB, dissociates into ions, so the acid exists mostly as undissociated HB molecules inwater.a.b.c.d.e.33.HNO2: weak acid beakerHNO3: strong acid beakerHCl: strong acid beakerHF: weak acid beakerHC2H3O2: weak acid beakerThe Ka value is directly related to acid strength. As Ka increases, acid strength increases. Forwater, use Kw when comparing the acid strength of water to other species. The Ka values are:HClO4: strong acid (Ka 1); HClO2: Ka 1.2 10 2NH4 : Ka 5.6 10 10 ; H2O: Ka Kw 1.0 10 14From the Ka values, the ordering is: HClO4 HClO2 NH4 H2O.34.Except for water, these are the conjugate bases of the acids in the previous exercise. In general,the weaker the acid, the stronger the conjugate base. ClO4 is the conjugate base of a strong acid;it is a terrible base (worse than water). The ordering is: NH3 ClO2 H2O ClO4 35.a. HCl is a strong acid and water is a very weak acid with Ka Kw 1.0 10 14 . HCl is amuch stronger acid than H2O.b. H2O, Ka Kw 1.0 10 14 ; HNO2, Ka 4.0 10 4 ; HNO2 is a stronger acid than H2Obecause Ka for HNO2 Kw for H2O.c. HOC6H5 , Ka 1.6 10 10 ; HCN, Ka 6.2 10 10 ; HCN is a stronger acid than HOC6H5because Ka for HCN Ka for HOC6H5.36.a. H2O; The conjugate bases of strong acids are terrible bases (Kb 10 14 ).
496CHAPTER 14ACIDS AND BASESb. NO2 ; The conjugate bases of weak acids are weak bases ( 10 14 Kb 1).c. OC6H5 ; For a conjugate acid-base pair, Ka Kb Kw. From this relationship, the strongerthe acid the weaker the conjugate base (Kb decreases as Ka increases). Because HCN is astronger acid than HOC6H5 (Ka for HCN Ka for HOC6H5), OC6H5 will be a stronger basethan CN-.Autoionization of Water and the pH Scale37.38.39.At 25 C, the relationship: [H ] [OH ] Kw 1.0 10 14 always holds for aqueous solutions.When [H ] is greater than 1.0 10 7 M, the solution is acidic; when [H ] is less than 1.0 10 7 M, the solution is basic; when [H ] 1.0 10 7 M, the solution is neutral. In terms of[OH ], an acidic solution has [OH ] 1.0 10 7 M, a basic solution has [OH ] 1.0 10 7 M,and a neutral solution has [OH ] 1.0 10 7 M.a. [OH ] K w 1.0 10 14 1.0 10-7 M; The solution is neutral.[H ] 1.0 10 7b. [OH ] 1.0 10 14 12 M; The solution is basic.8.3 10 16c. [OH ] 1.0 10 14 8.3 10 16 M; The solution is acidic.12d. [OH ] 1.0 10 14 1.9 10 10 M; The solution is acidic.5.4 10 5a. [H ] Kw1.0 10 14 6.7 10 15 M; basic1.5[OH ]b. [H ] 1.0 10 14 2.8 M; acidic3.6 10 15c. [H ] 1.0 10 14 1.0 10 7 M; neutral 71.0 10d. [H ] 1.0 10 14 1.4 10 11 M; basic7.3 10 4a. Because the value of the equilibrium constant increases as the temperature increases, thereaction is endothermic. In endothermic reactions, heat is a reactant so an increase intemperature (heat) shifts the reaction to produce more products and increases K in theprocess.b. H2O(l) H (aq) OH (aq)Kw 5.47 10 14 [H ][OH ] at 50. CIn pure water [H ] [OH ], so 5.47 10 14 [H ]2, [H ] 2.34 10 7 M [OH ]
CHAPTER 1440.ACIDS AND BASESa. H2O(l) H (aq) OH (aq)497Kw 2.92 10 14 [H ] [OH ]In pure water [H ] [OH ], so 2.92 10 14 [H ]2, [H ] 1.71 10 7 M [OH ]b. pH log [H ] log (1.71 10 7 ) 6.767c. [H ] Kw/[OH ] 2.92 10 14 /0.10 2.9 10 13 M; pH log (2.9 10 13 ) 12.5441.pH log [H ]; pOH log [OH-]; At 25 C, pH pOH 14.00; For Exercise 13.37:a. pH log [H ] log (1.0 10 7 ) 7.00; pOH 14.00 pH 14.00 7.00 7.00b. pH log (8.3 10 16 ) 15.08; pOH 14.00 15.08 1.08c. pH log (12) 1.08; pOH 14.00 ( 1.08) 15.08d. pH log (5.4 10 5 ) 4.27; pOH 14.00 4.27 9.73Note that pH is less than zero when [H ] is greater than 1.0 M (an extremely acidic solution).For Exercise 13.38:a. pOH log [OH ] log (1.5) 0.18; pH 14.00 pOH 14.00 ( 0.18) 14.18b. pOH log (3.6 10 15 ) 14.44; pH 14.00 14.44 0.44c. pOH log (1.0 10 7 ) 7.00; pH 14
CHAPTER 14 ACIDS AND BASES 487 Weak acids are only partially dissociated in water. We say that the equilibrium lies far to the left, thus giving values for K a 1. (We have mostly reactants at equilibrium and few products present). The conjugate bases of weak acids are better bases than water. When we have a solution
2. Describe the common properties of acids and bases 3. Identify acids and bases using indicators, pH papers 4. Name some common lab acids and bases, acids at and bases at home 5. Describe reactions of acids with metals, bases and carbonates 6. Describe the application of acids, bases and p
_7. Which statement describes an alternate theory of acids and bases? (1) Acids and bases are both H acceptors. (2) Acids and bases are both H donors. (3) Acids are H acceptors, and bases are H donors. (4) Acids are H donors, and bases are H acceptors. _8. Which substance is the
Properties of Acids and Bases Return to the Table of contents Slide 5 / 208 What is an Acid? Acids release hydrogen ions into solutions Acids neutralize bases in a neutralization reaction. Acids corrode active metals. Acids turn blue litmus to red. Acids taste sour. Properties of Acids Slide 6 / 208 Properties
Lecture Notes for Chapter 16: Acids and Bases I. Acids and Bases a. There are several ways to define acids and bases. Perhaps the easiest way to start is to list some of the properties of acids and bases. b. The table below summarizes some properties that will be helpful
Acids, Bases, and pH The hydrohalic acids (HX (aq)), where X represents a halogen) include HF, HCl, HBr, and HI. Only HF is a weak acid. The rest are strong acids. What factors account for this difference? 8.1 Explaining the Properties of Acids and Bases 8.2 The Equilibrium of Weak Acids and Bases 8.3
properties of acids and bases. 5. Describe the colors that form in acidic and basic solutions with litmus paper and phenolphthalein. 6. Explain the difference between strong acids or bases and weak acids or bases. 7. Memorize the strong acids and bases. 8. Define the terms polyprotic and amphiprotic. 9. Perform calculations using the following .
Unit 12 Acids and Bases- Funsheets Part A: Name and write the formula for the following acids and bases. 1) Carbonic acid _ . Part E: Using your knowledge of acids and bases, answer the following questions. 1) Fill in the following Venn diagram about properties of acids and bases. You must fill in at least 4 facts in each.
ABR ¼ American Board of Radiology; ARRS ¼ American Roentgen Ray Society; RSNA ¼ Radiological Society of North America. Table 2 Designing an emergency radiology facility for today Determine location of radiology in the emergency department Review imaging statistics and trends to determine type and volume of examinations in emergency radiology Prepare a comprehensive architectural program .
