Acids And Bases Properties Of Acids

Slide 46 / 174Autoionization of Water· As we have seen, water is amphoteric, meaning that itcan act as either an acid or a base.· In pure water, a few molecules act as bases and a fewact as acids, in a process referred to as autoionization.HOH HOHOH OH-HH· The double headed arrow indicates that both theforward and reverse reactions occur simultaneously.H2O (l) H2O (l) H3O (aq) OH- (aq)Autoionization of WaterSlide 47 / 174H2O (l) H2O (l) H3O (aq) OH- (aq)· When there is an equilibrium state, the ratio ofproducts to reactants yields a constant.· This value is known as the equilibrium constant, Kand will be discussed in more depth later in thisunit.· All concentrations are in M, molarity, asdesignated by brackets, [ ].K [H3O ] x [OH-][H2O] x [H2O]Ion-Product Constant· In most dilute acid and base solutions, the concentrationof undissociated water, remains more or less a constant.We can thus disregard the denominator in the equilibriumexpression.· So,K [H3O ] x [OH-][H2O] x [H2O]becomesKw [H3O ] x [OH-]Slide 48 / 174

Slide 49 / 174Ion-Product ConstantKw [H3O ] x [OH-]· This special equilibrium constant, Kw is referred to asthe ion-product constant for water.· At 25 C, Kw 1.0 x 10-14. Since this is such a smallnumber, we conclude that pure water contains relativelyvery few ions.20The magnitude of Kw indicatesthatA21Slide 50 / 174water ionizes to a very small extentBthe autoionization of water is exothermicCwater ionizes very quicklyDwater ionizes very slowlyThe ion-product constant forwater, Kw is represented byABCD[H2O]2[H3O ] x [OH-][H3O ] [OH-][H3O ] - [OH-]Slide 51 / 174

Slide 52 / 174pH· It is a measure of hydrogen ion concentration, [H ]in a solution, where the concentration is measured inmoles H per liter, or molarity.· The pH scale ranges from 0-14.· pH is defined as the negative base-10 logarithm ofthe concentration of hydronium ion.pH -log [H3O ]Slide 53 / 174pH· pH is defined as the negative base-10 logarithm of theconcentration of hydronium ion.pH -log [H3O ]Hydrogen ionconcentration, [H ]in moles/LiterpH1.0 x 10-11-22-10101.0 x 101.0 x 10Is the relationship between [H ] and pH a direct or an inverse one?pHBecause of the base-10 logarithm, each 1.0-point valueon the pH scale differs by a value of ten.A solution with pH 9 has a hydrogen ionconcentration, [H ], that is ten times more than a pH 10 solution.A solution with pH 8 has a hydrogen ionconcentration, [H ], that is 102 or 100 times more thana pH 10 solution.A solution with pH 7 has a hydrogen ionconcentration, [H ], that is 103 or 1000 times more thana pH 10 solution.Slide 54 / 174

pHSlide 55 / 174· Recall that in pure water, the ion-product isKw 1.0 10-14· In pure water, the hydronium ion concentration andhydroxide ion concentrations are equal:[H3O ] [OH-]· Therefore, in pure water,[H3O ] 1.0 10-14 1.0 x 10-7 Mand[OH-] 1.0 10-14 1.0 x 10-7 MSlide 56 / 17422The molar concentration ofhydronium ion, [H3O ], in purewater at 25 C is .A0B1C7D10-7E10-1423A solution with pH 3 has ahydrogen ion concentration thatis than a solutionwith pH 5.A2x moreB2x lessC100x more100x lessDSlide 57 / 174

24Slide 58 / 174A solution with pH 14 has ahydrogen ion concentration thatis than a solutionwith pH 11.ABCD3x more3x less1000x more1000x lessSlide 59 / 174pH· Therefore, in pure water,pH -log [H3O ] 7.00pH -log (1.0 10-7) 7.00· An acid has a higher [H3O ] than pure water, so its pH is 7.· A base has a lower [H3O ] than pure water, so its pH is 7.Solution typeAcidicNeutralBasic[H ](M)[OH-] (M) 1.0x10-7-7 1.0x10 1.0x10-7 1.0x10-7-7 1.0x10 1.0x10-7pH value 7.00 7.00 7.00Slide 60 / 174pHACIDBASE[H ] [OH-]There are excesshydrogen ions insolution.[H ] [OH-]There are excesshydroxide ions insolution.Solution typeAcidicNeutralBasic[H ](M)-7 1.0x10 1.0x10-7 1.0x10-7[OH-] (M)-7 1.0x10 1.0x10-7 1.0x10-7pH value 7.00 7.00 7.00

2526For a basic solution, thehydrogen ion concentration isthan thehydroxide ion concentration.Agreater thanBless thanCequal toDNot enough information.For an acidic solution, thehydroxide ion concentration isthan thehydrogen ion concentration.ABCD27Slide 62 / 174greater thanless thanequal toNot enough information.Which solution below hasthe highest concentrationof hydroxide ions?ABCDSlide 61 / 174pH 3.21pH 7.00pH 8.93pH 12.6Slide 63 / 174

28Slide 64 / 174Which solution below hasthe lowest concentration ofhydrogen ions?ABCDpH 11.4pH 8.53pH 5.91pH 1.98These are thepH values forseveral commonsubstances.More acidicSlide 65 / 174pHBattery acidgastric fluidlemon juicepure rain or watercarbonatedbeveragesvinegarorange juicebeercoffeeegg yolksmilkdistilled watersea waterbaking sodabloodmilk of magnesiaMore basichousehold ammonia29household bleachhousehold lyeFor a 1.0-M solution of a weakbase, a reasonable pH wouldbe .A2B6C7D9E13Slide 66 / 174

30For a 1.0-M solution of a strongacid, a reasonable pH wouldbe .A2B6C7D9E13Slide 67 / 174Slide 68 / 17431A solution with the pH of 5.0A is basicBhas a hydrogen ion concentration of 5.0MC is neutralD has a hydroxide-ion concentration of 1x10-9Slide 69 / 17432The pH of a solution with a concentration of 0.01Mhydrochloric acid isA 10-2B12C 2D 10-12

Slide 70 / 174How Do We Measure pH?For less accurate measurements, one can use Litmus paper· “Red” litmus paper turns blue above pH 8· “Blue” litmus paper turns red below pH 5Or an indicator (usually an organic dye) such as one of the following:pH range for color change02648101214Methyl violetThymol blueMethyl orangeMethyl redBromothymol bluePhenolphthaleinAlizarin yellow RHow Do We Measure pH?Slide 71 / 174For more accuratemeasurements, oneuses a pH meter, whichmeasures the voltage inthe solution.How Do We Calculate pH?Recall that pH is defined as the negative base-10logarithm of the concentration of hydronium ion (orhydrogen ion).pH -log [H3O ]orpH -log [H ]Slide 72 / 174

How Do We Calculate pH?Slide 73 / 174What is the pH of the solution with hydrogen ionconcentration of 5.67 x 10-8 M (molar)?pH -log [H ]First, take the log of 5.67 x 10-8 -7.246Now, change the sign from - to Answer: pH 7.246If you take the log of -5.67 x 10-8, you will end upwith an incorrect answer.The order of operations: 1. Take the log2. Switch the signSlide 74 / 17433What is the pH of a solution with a hydrogen ionconcentration of 1 x 10-5 M?A1 x 10-5B-5C5D9Slide 75 / 17434What is the pH of a solution with a hydrogen ionconcentration of 1 x 10-12 M?A1 x 10-12B12C2D-12

35What is the pH of an aqueous solutionat 25.0 C in which [H ] is 0.0025 M?ABCDE3.42.6-2.6-3.42.2536 What is the pH of an aqueoussolution at 25.0 C in which [H ] is0.025 M?ABCDESlide 76 / 174Slide 77 / 174 1.60-1.60 12.4-12.4-1.25Additional pH calculationsIf you are given the pH and asked to find the [H ](or [H3O ]) in a solution, use the inverse log.Since pH -log [H ], then[H ] 10-pHWhat is the hydrogen ion concentration (M) in asolution of Milk of Magnesia whose pH 9.8?[H ] 10-9.8[H ] 1.58 x 10-10 M or mol/LiterSlide 78 / 174

3738What is the pH of a solutionwhose hydronium ionconcentration is 7.14 x 10-3 M?What is the pH of a solutionwhose hydronium ionconcentration is 1.92 x 10-9 M?Slide 79 / 174Slide 80 / 174Slide 81 / 17439What is the hydronium ion concentrationin a solution whose pH 4.29?

Slide 82 / 1744041What is the hydroxide ion concentrationin a solution whose pH 4.29?The pH of an aqueous solutionis 11.58. What is the molarity ofthe hydrogen ion, H ?Slide 83 / 174Answer2.63x 10-12 MOther “p” Scales· The “p” in pH tells us to take the negative base-10logarithm of the quantity (in this case, hydronium ions).Some similar examples are· pOH -log [OH-]· pKw -log Kw· pKa -log KaSlide 84 / 174

Relationship between pH and pOHBecauseSlide 85 / 174[H3O ] [OH-] Kw 1.0 x 10-14,we know that-log [H3O ] -log [OH-] -log Kw 14.00or, in other words,pH pOH pKw 14.00Slide 86 / 17442 An aqueous solution of an acid has a hydrogen ionconcentration of 2.5x10-4. What is the OH- ionconcentration of this solution?A 4.0x10-11B5.0x10-11C 4.5x10-8D 7.5x10-11E4.0x10-7Slide 87 / 17443 An aqueous solution has a hydrogen ionconcentration of 1.5x10-12. What is the pH of thissolution?Report your answer to 3 significant figures.

Acid Dissociation ConstantsSlide 88 / 174HA (aq) H2O (l) A- (aq) H3O (aq)· For a generalized acid dissociation, the equilibrium expression would beKc, AKA Ka [H3O ] [A-][HA]· This equilibrium constant is called the acid-dissociation constant, Ka.Ka [H3O ] [A-][HA]Acid Dissociation ConstantsSlide 89 / 174The greater the value of Ka, the stronger is the acid.44The acid dissociation constant (Ka) of HF is 6.7 x 10-4.Which of the following is true of a 0.1M solution of HF?A [HF] is greater than [H ][F-]B[HF] is less than [H ][F-]C [HF] is equal to [H ][F-]D [HF] is equal to [H-][F ]Ka [H3O ] [A-][HA]Slide 90 / 174

Calculating Ka from the pHSlide 91 / 174The pH of a 0.10 M solution of formic acid,HCOOH, at 25 C is 2.38. Calculate Ka for formicacid at this temperature.The dissociation equation for formic acid may bewritten as a reaction with waterHCOOH H2O HCOO- H3O or, without waterHCOOH HCOO- H Calculating Ka from the pHSlide 92 / 174HCOOH H2O HCOO- H3O From this dissociation equation, wecan obtain the Ka expression:Ka [H3O ][HCOO-][HCOOH]Weak Acids:Calculating Ka from the pHThe pH of a 0.10 M solution of formic acid,HCOOH, at 25 C is 2.38. Calculate Ka for formicacid at this temperature.To calculate Ka, we need the equilibriumconcentrations of all three things.We can find [H3O ], which is the same as[HCOO-], from the pH.Slide 93 / 174

Weak Acids:Calculating Ka from the pHSlide 94 / 174pH -log [H3O ]2.38 -log [H3O ]-2.38 log [H3O ]10-2.38 10log [H3O ] [H3O ]4.2 x 10-3 M [H3O ] [HCOO-]Note that this is a monoprotic acid, so[acid] [conjugate base]Weak Acids:Calculating Ka from the pHSlide 95 / 174Now, we substitute values into the Ka expression and solve:Ka Ka Ka[H3O ][HCOO-][HCOOH][4.2 10-3] [4.2 10-3][0.10] 1.8 10-4Calculating Percent IonizationOne way to compare the strength of two acids is by theextent to which each one ionizes. This is done bycalculating percent ionization, or the ratio of [H ] ionsthat are produced, compared to the original acidconcentration.Percent Ionization [H3O ]eq[HA]initial 100Slide 96 / 174

Calculating Percent IonizationPercent Ionization [H3O ]eq[HA]initialSlide 97 / 174 100In this example[H3O ]eq 4.2 10-3 M[HCOOH]initial 0.10 MPercent Ionization 4.2 x 10-30.10 1004.2 %Calculating Percent IonizationSlide 98 / 174What would be the analogous formula tocalculate percent ionization for a base?Percent Ionization [OH-]eq[Base]initial 100Slide 99 / 174Calculating pH from KaCalculate the pH of a 0.30 M solution of acetic acid,HC2H3O2, at 25 C. Ka for acetic acid at 25 C is 1.8 x 10-5.First, we write the dissociation equation for acetic acidHC2H3O2 (aq) H2O (l) H3O (aq) C2H3O2- (aq)

Slide 100 / 174Calculating pH from KaCalculate the pH of a 0.30 M solution of acetic acid,HC2H3O2, at 25 C. Ka for acetic acid at 25 C is 1.8 x 10-5.From the dissociation equation, we obtainthe equilibrium constant expression:Ka [H3O ][C2H3O2-][HC2H3O2]Slide 101 / 174Calculating pH from KaCalculate the pH of a 0.30 M solution of acetic acid, HC2H3O2,at 25 C. Ka for acetic acid at 25 C is 1.8 x 10-5.We next set up an ICE chart.[H3O ], M[HC2H3O2], MInitialChangeEquilibrium[C2H3O2-], M0.30 M00-x x xabout 0.30 MxxWe are assuming that x will be very small comparedto 0.30 and can, therefore, be ignored.Calculating pH from KaCalculate the pH of a 0.30 M solution of acetic acid,HC2H3O2, at 25 C. Ka for acetic acid at 25 C is 1.8 x 10-5.Now, substituting values from the ICE chart into the Kaexpression yields1.8 10-5 (x)2(0.30)(1.8 10-5) (0.30) x25.4 x 10-6 x22.3 x 10-3 xRemember whatyour "x" is !In this case, it's[H3O ], but othertimes it's [OH-].Slide 102 / 174

Calculating pH from KaSlide 103 / 174Calculate the pH of a 0.30 M solution of acetic acid,HC2H3O2, at 25 C. Ka for acetic acid at 25 C is 1.8 x 10-5.pH -log [H3O ]pH -log (2.3 x 10-3)pH 2.64Significant figure rules for pH on the AP exam:· The calculated pH value should have as many DECIMAL places asthe [H ] has sig figs.· So if the [H ] has 2 sig figs, report the pH to the 0.01 place value.· If the [H ] has 3 sig figs, report the pH to the 0.001 place value.Slide 104 / 17445What is the hydrogen ion concentration if the aciddissociation constant is 1 x 10-6 and the acidconcentration is 0.01M?A 10-6B10-5C 10-4D 10-3Ka [H3O ] [A-][HA]Slide 105 / 17446What is the concentration of the acid if the pH is 4 andthe Ka is 1 x 10-7?A 10-7B10-5C 10-3D 10-1Ka [H3O ] [A-][HA]

Polyprotic Acids Slide 106 / 174Polyprotic acids are characterized byhaving more than one acidic proton.Here are some examples:Sulfuric acidH2SO4Phosphoric acidH3PO4Carbonic acidH2CO3Oxalic acidH 2C 2O 4Polyprotic AcidsSlide 107 / 174Polyprotic acids have a Ka value for each protonthat can be removed.For example, consider carbonic acid, H2CO3.The first ionization equation for carbonic acid isH2CO3 H2O -- -- HCO3- H3O Write the Ka expression for this equation. This isreferred to as Ka1.Polyprotic AcidsThe second ionization equation for carbonic acid isHCO3- H2O -- -- CO32- H3O Write the Ka expression for this equation. This isreferred to as Ka2.Slide 108 / 174

Polyprotic AcidsSlide 109 / 174Now, we examine both dissociation constants.H2CO3 H2O -- -- HCO3- H3O Ka1 HCO3- H2O -- -- CO32- H3O [HCO3-][H3O ]Ka2 [H2CO3][CO32-][H3O ][HCO3-]Polyprotic AcidsSlide 110 / 174Notice that the bicarbonate ion, HCO3-, appears ineach expression; in the numerator for Ka1 and in thedenominator for Ka2.Ka1 x Ka2 [HCO3-][H3O ] [CO32-][H3O ]Ka1 x Ka2 [H2CO3][HCO3-][HCO3-][H3O ] [CO32-][H3O ][H2CO3][HCO3-]Polyprotic AcidsThe equation for the complete ionization of carbonic acid isH2CO3 H2O -- -- CO32- 2 H3O and the Ka expression for this reaction isK [CO32-][H3O ]2Ka1 x Ka2 [H2CO3][HCO3-][H3O ] [CO32-][H3O ][H2CO3][HCO3-]Ka1 x Ka2 overall KSo, the product of Ka1 x Ka2 for a diprotic acid yields theoverall K for complete dissociation.Slide 111 / 174

Slide 112 / 174Polyprotic AcidsGenerally, the pH of polyprotic acids dependsonly on the removal of the first proton.This holds true when the difference betweenthe Ka1 and Ka2 values is at least 103.Slide 113 / 17447The Ka of carbonic acid is 4.3 x 10H2CO3 -- H HCO3--7This means that H2CO3 is a .A good hydrogen-ion acceptorBgood hydrogen-ion donorC poor hydrogen-ion acceptorD poor hydrogen-ion donorSlide 114 / 17448A diprotic acid, H2X, has the followingdissdiprotic ociation constants:Ka1 2.0 x 10-4Ka2 3.0 x 10-6What is the overall K value for this acid?A 5.0 X 10-10B6.0 X 10-10C 5.0 X 10-24D 6.0 x 10-24E6.0 x 1024

Weak BasesSlide 115 / 174Bases react with water to produce hydroxide ion.Even though NH3 does not have the hydroxide ion, OH-, in itsformula, note that it is a base according to both the Arrenhiusand Bronsted-Lowry definitions.Weak BasesSlide 116 / 174B- H2O HB OH-The equilibrium constant expression for thisreaction isKb [HB][OH-][B-]where Kb is the base-dissociation constant.Just as for Ka, the stronger a base is, it will have a higher Kbvalue. In fact, since the strong bases dissociate 100%, theirKb values are referred to as "very large".Weak BasesKb can be used to find [OH-] and, ultimately, pH.Slide 117 / 174

Slide 118 / 17449Which base has the smallest base dissociationconstant, Kb?A potassium hydroxideBsodium hydroxideC calcium hydroxideD ammoniaSlide 119 / 17450A base has a dissociation constant, Kb 2.5 x 10-11.Which of the following statements is true?A This is a concentrated base.BThis base ionizes slightly in aqueous solution.C This is a strong base.D An aqueous solution of this would be acidic.51A substance with a Ka of 1x10-5 would be classified asa .ABstrong acidweak acidC strong baseD weak baseSlide 120 / 174

Slide 121 / 174Weak BasesMost problems involving weak bases requireyou to calculate either· pHor· the base-dissociation constant, Kb.pH of Basic SolutionsSlide 122 / 174What is the pH of a 0.15 M solution of NH3?NH3 (aq) H2O (l) NH4 (aq) OH- (aq)As with weak acids, first write the equilibrium expressionfor the dissociation equation. Obtain the Kb value from anearlier page.Kb [NH4 ][OH-] 1.8 x 10-5[NH3]pH of Basic SolutionsWhat is the pH of a 0.15 M solution of NH3?NH3 (aq) H2O (l) NH4 (aq) OH- (aq)Tabulate the data[NH3], M[NH4 ], M[OH-], MInitially0.1500Change-x x xxxAt015 - x Equilibrium0.15Slide 123 / 174

pH of Basic Solutions1.8 10-5 Slide 124 / 174(x)2(0.15)(1.8 10-5) (0.15) x22.7 x 10-6 x21.6 x 10-3 xAgain, remember what your "x" is !pH of Basic SolutionsSlide 125 / 174In this case, "x" is [OH-].Therefore,[OH-] 1.6 x 10-3 MpOH -log (1.6 x 10-3)pOH 2.80So, now solving for pH:pH 14.00 - 2.80pH 11.20Ka and KbFor a conjugate acid-base pair, Ka and Kb are relatedin a special way.Write the ionization equations for the following:1) reaction of ammonia (NH3) and water2) reaction of ammonium ion (NH4 ) and waterSlide 126 / 174

Slide 127 / 174Ka and KbNH3 H2O NH4 OH-NH4 H2O NH3 H3O Write the corresponding equilibrium constant expressionfor each of these equations.Which of these expressions is referred to as "Ka"?Which is referred to as "Kb"?Slide 128 / 174Ka and KbNH3 H2O NH4 OH-Kb [NH4 ][OH-][NH3]NH4 H2O NH3 H3O Ka [NH3][H3O ][NH4 ]What do these expressions have in common?Ka and KbKb x Ka [NH4 ][OH-] [NH3][H3O ][NH3][NH4 ]Kb x Ka [NH4 ][OH-] [NH3][H3O ][NH4 ][NH3]Kb x Ka [OH-][H3O ] KwSo, the product of Ka x Kb for any conjugate acid-base pairyields the ion-product constant, Kw.Slide 129 / 174

Slide 130 / 174Ka and KbFor a specific conjugate acid-base pair, Ka and Kbare related in this way:Ka x Kb KwTherefore, if you know the value of one of them, youcan calculate the other.Slide 131 / 17452For the acid HCN, what is the equation on which the Kaexpression is based?A HCN -- OH - HCNBHCN -- OH - CN-C HCN H2O -- CN- H3O D HCN H2O -- OH - CN-Slide 1

Dec 06, 2011 · Arrhenius Acids and Bases A definition of acids and bases from the 1800's Considered obsolete now since it only relates to reactions in water, aqueous solutions. He defined acids and bases thi