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Acidsbase2

  1. 1. Chapter “Acids, Bases, and Salts”
  2. 2. Section 1Section 1 Acid-Base TheoriesAcid-Base Theories OBJECTIVES:OBJECTIVES: –Define the properties of acids and bases.
  3. 3. Section 19.1Section 19.1 Acid-Base TheoriesAcid-Base Theories OBJECTIVES:OBJECTIVES: –Compare and contrast acids and bases as defined by the theories of: a) Arrhenius, b) Brønsted-Lowry, and c) Lewis.
  4. 4. Properties of AcidsProperties of Acids They tasteThey taste soursour (don’t try this at home).(don’t try this at home). They canThey can conduct electricityconduct electricity.. –Can be strong or weak electrolytes in aqueous solution React with metalsReact with metals to form Hto form H22 gas.gas. Change the colorChange the color of indicatorsof indicators (for example: blue litmus turns to red).(for example: blue litmus turns to red). React with basesReact with bases (metallic hydroxides)(metallic hydroxides) to form water and a salt.to form water and a salt.
  5. 5. Properties of AcidsProperties of Acids They have aThey have a pH of less than 7pH of less than 7 (more(more on this concept of pH in a later lesson)on this concept of pH in a later lesson) TheyThey react with carbonates andreact with carbonates and bicarbonatesbicarbonates to produce a salt, water,to produce a salt, water, and carbon dioxide gasand carbon dioxide gas How do you know if a chemical is anHow do you know if a chemical is an acid?acid? – It usually starts with Hydrogen. – HCl, H2SO4, HNO3, etc. (but not water!)
  6. 6. Acids Affect Indicators, byAcids Affect Indicators, by changing their colorchanging their color Blue litmus paper turns red in contact with an acid (and red paper stays red).
  7. 7. AcidsAcids have ahave a pHpH lessless than 7than 7
  8. 8. Acids React with Active MetalsAcids React with Active Metals Acids react with active metals to form salts and hydrogen gas: HCl(aq) + Mg(s) → MgCl2(aq) + H2(g) This is a single-replacement reaction
  9. 9. Acids React with CarbonatesAcids React with Carbonates and Bicarbonatesand Bicarbonates HCl + NaHCO3 NaCl + H2O + CO2 Hydrochloric acid + sodium bicarbonate salt + water + carbon dioxide An old-time home remedy for relieving an upset stomach
  10. 10. Effects ofEffects of Acid RainAcid Rain on Marbleon Marble (marble is calcium(marble is calcium carbonatecarbonate)) George Washington: BEFORE acid rain George Washington: AFTER acid rain
  11. 11. AcidsAcids NeutralizeNeutralize BasesBases HCl + NaOH → NaCl + H2O -Neutralization reactions ALWAYS produce a salt (which is an ionic compound) and water. -Of course, it takes the right proportion of acid and base to produce a neutral salt
  12. 12. Sulfuric AcidSulfuric Acid = H= H22SOSO44 Highest volumeHighest volume production ofproduction of anyany chemical in the U.S.chemical in the U.S. (approximately 60 billion pounds/year)(approximately 60 billion pounds/year) Used in the productionUsed in the production of paperof paper Used in production ofUsed in production of fertilizersfertilizers Used in petroleumUsed in petroleum refining; auto batteriesrefining; auto batteries
  13. 13. Nitric AcidNitric Acid = HNO= HNO33 Used in the productionUsed in the production of fertilizersof fertilizers Used in the productionUsed in the production of explosivesof explosives Nitric acid is aNitric acid is a volatilevolatile acid – its reactiveacid – its reactive components evaporatecomponents evaporate easilyeasily Stains proteins yellowStains proteins yellow (including skin!)(including skin!)
  14. 14. Hydrochloric AcidHydrochloric Acid = HCl= HCl Used in the “pickling”Used in the “pickling” of steelof steel Used to purifyUsed to purify magnesium from seamagnesium from sea waterwater Part of gastric juice, itPart of gastric juice, it aids in the digestion ofaids in the digestion of proteinsproteins Sold commercially asSold commercially as Muriatic acidMuriatic acid
  15. 15. Phosphoric AcidPhosphoric Acid = H= H33POPO44 A flavoring agent inA flavoring agent in sodas (adds “tart”)sodas (adds “tart”) Used in theUsed in the manufacture ofmanufacture of detergentsdetergents Used in theUsed in the manufacture ofmanufacture of fertilizersfertilizers NotNot a commona common laboratory reagentlaboratory reagent
  16. 16. Acetic AcidAcetic Acid = HC= HC22HH33OO22 (also called Ethanoic Acid, CH(also called Ethanoic Acid, CH33COOH)COOH) Used in theUsed in the manufacture of plasticsmanufacture of plastics Used in makingUsed in making pharmaceuticalspharmaceuticals Acetic acid is the acidAcetic acid is the acid that is present inthat is present in householdhousehold vinegarvinegar
  17. 17. Properties of BasesProperties of Bases (metallic hydroxides)(metallic hydroxides) React with acidsReact with acids to form waterto form water and a salt.and a salt. TasteTaste bitterbitter.. Feel slipperyFeel slippery (don’t try this either).(don’t try this either). Can be strong or weakCan be strong or weak electrolyteselectrolytes in aqueous solutionin aqueous solution Change the colorChange the color of indicatorsof indicators (red litmus turns blue).(red litmus turns blue).
  18. 18. Examples of BasesExamples of Bases (metallic hydroxides)(metallic hydroxides)  Sodium hydroxide,Sodium hydroxide, NaOHNaOH ((lye for drain cleaner; soaplye for drain cleaner; soap))  Potassium hydroxide,Potassium hydroxide, KOHKOH ((alkaline batteriesalkaline batteries))  Magnesium hydroxide,Magnesium hydroxide, Mg(OH)Mg(OH)22 ((Milk of MagnesiaMilk of Magnesia))  Calcium hydroxide,Calcium hydroxide, Ca(OH)Ca(OH)22 ((limelime;; masonrymasonry))
  19. 19. Bases Affect IndicatorsBases Affect Indicators Red litmus paper turns blue in contact with a base (and blue paper stays blue). Phenolphthalein turns purple in a base.
  20. 20. BasesBases have ahave a pHpH greatergreater than 7than 7
  21. 21. Bases Neutralize AcidsBases Neutralize Acids Milk of Magnesia contains magnesium hydroxide, Mg(OH)2, which neutralizes stomach acid, HCl. 2 HCl + Mg(OH)2 MgCl2 + 2 H2O Magnesium salts can cause diarrhea (thus they are used as a laxative) and may also cause kidney stones.
  22. 22. Acid-Base TheoriesAcid-Base Theories
  23. 23. Svante ArrheniusSvante Arrhenius He was a Swedish chemist (1859-He was a Swedish chemist (1859- 1927), and a Nobel prize winner in1927), and a Nobel prize winner in chemistry (1903)chemistry (1903) one of the first chemists to explainone of the first chemists to explain the chemical theory of the behaviorthe chemical theory of the behavior of acids and basesof acids and bases Dr. Hubert Alyea (professor emeritusDr. Hubert Alyea (professor emeritus at Princeton University) was the lastat Princeton University) was the last graduate student of Arrhenius.graduate student of Arrhenius.
  24. 24. Hubert N. Alyea (1903-1996)Hubert N. Alyea (1903-1996)
  25. 25. 1. Arrhenius Definition - 18871. Arrhenius Definition - 1887 AcidsAcids produce hydrogen ions (Hproduce hydrogen ions (H1+1+ )) inin aqueous solutionaqueous solution (HCl(HCl →→ HH1+1+ + Cl+ Cl1-1- )) BasesBases produce hydroxide ionsproduce hydroxide ions (OH(OH1-1- ) when dissolved) when dissolved in waterin water.. (NaOH → Na1+ + OH1- ) Limited toLimited to aqueous solutionsaqueous solutions.. Only one kind of base (hydroxides)Only one kind of base (hydroxides) NHNH33 (ammonia) could not be an(ammonia) could not be an Arrhenius base: no OHArrhenius base: no OH1-1- produced.produced.
  26. 26. Svante Arrhenius (1859-1927)Svante Arrhenius (1859-1927)
  27. 27. Polyprotic Acids?Polyprotic Acids? Some compounds haveSome compounds have more thanmore than one ionizable hydrogenone ionizable hydrogen to releaseto release HNOHNO33 nitric acid -nitric acid - monomonoproticprotic HH22SOSO44 sulfuric acid -sulfuric acid - didiprotic - 2 Hprotic - 2 H++ HH33POPO44 phosphoric acid -phosphoric acid - tritriprotic - 3protic - 3 HH++ Having more than one ionizableHaving more than one ionizable hydrogen doeshydrogen does notnot mean stronger!mean stronger!
  28. 28. AcidsAcids Not all compounds that haveNot all compounds that have hydrogen are acids. Water?hydrogen are acids. Water? Also, not all the hydrogen in anAlso, not all the hydrogen in an acid may be released as ionsacid may be released as ions –only those that have very polar bonds are ionizable - this is when the hydrogen is joined to a very electronegative element
  29. 29. Arrhenius examples...Arrhenius examples... Consider HCl = it is an acid!Consider HCl = it is an acid! What about CHWhat about CH44 (methane)?(methane)? CHCH33COOH (ethanoic acid, alsoCOOH (ethanoic acid, also called acetic acid) - it has 4called acetic acid) - it has 4 hydrogens just like methanehydrogens just like methane does…?does…? Table 19.2, p. 589 for bases,Table 19.2, p. 589 for bases, which are metallic hydroxideswhich are metallic hydroxides
  30. 30. Organic AcidsOrganic Acids (those with carbon)(those with carbon) Organic acids all contain the carboxyl group, (-COOH), sometimes several of them. CH3COOH – of the 4 hydrogen, only 1 ionizable The carboxyl group is a poor proton donor, so ALL organic acids are weak acids. (due to being bonded to the highly electronegative Oxygen)
  31. 31. 2. Brønsted-Lowry - 19232. Brønsted-Lowry - 1923 A broader definition than ArrheniusA broader definition than Arrhenius AcidAcid is hydrogen-ion donor (His hydrogen-ion donor (H++ oror proton);proton); basebase is hydrogen-ion acceptor.is hydrogen-ion acceptor. Acids and bases always come in pairs.Acids and bases always come in pairs. HCl is an acid.HCl is an acid. –When it dissolves in water, it gives it’s proton to water. HClHCl(g)(g) + H+ H22OO(l)(l) ↔↔ HH33OO++ (aq)(aq) + Cl+ Cl-- (aq)(aq) Water is a base; makes hydronium ion.Water is a base; makes hydronium ion.
  32. 32. Johannes Brønsted Thomas LowryJohannes Brønsted Thomas Lowry (1879-1947) (1874-1936)(1879-1947) (1874-1936) DenmarkDenmark EnglandEngland
  33. 33. Why Ammonia is a BaseWhy Ammonia is a Base Ammonia can be explained as aAmmonia can be explained as a base by using Brønsted-Lowry:base by using Brønsted-Lowry: NHNH3(aq)3(aq) + H+ H22OO(l)(l) ↔ NH↔ NH44 1+1+ (aq)(aq) + OH+ OH1-1- (aq)(aq) Ammonia is the hydrogen ionAmmonia is the hydrogen ion acceptor (acceptor (basebase), and water is the), and water is the hydrogen ion donor (hydrogen ion donor (acidacid).). This causes the OHThis causes the OH1-1- concentration toconcentration to be greater than in pure water, andbe greater than in pure water, and the ammonia solution isthe ammonia solution is basicbasic
  34. 34. Acids and bases come inAcids and bases come in pairspairsA “A “conjugate baseconjugate base”” is the remainder ofis the remainder of the original acid, after itthe original acid, after it donatesdonates it’sit’s hydrogen ionhydrogen ion A “A “conjugate acidconjugate acid”” is the particleis the particle formed when the original baseformed when the original base gainsgains aa hydrogen ionhydrogen ion Thus, a conjugate acid-base pair is related byThus, a conjugate acid-base pair is related by thethe loss or gainloss or gain of aof a single hydrogen ionsingle hydrogen ion.. Chemical IndicatorsChemical Indicators?? They are weakThey are weak acids or bases that have a differentacids or bases that have a different color from their original acid and basecolor from their original acid and base
  35. 35. Acids and bases come inAcids and bases come in pairspairsGeneral equation is:General equation is: HAHA(aq)(aq) + H+ H22OO(l)(l) ↔↔ HH33OO++ (aq)(aq) + A+ A-- (aq)(aq) Acid + BaseAcid + Base ↔↔ Conjugate acid + Conjugate baseConjugate acid + Conjugate base NHNH33 + H+ H22OO ↔↔ NHNH44 1+1+ + OH+ OH1-1- basebase acidacid c.a. c.b.c.a. c.b. HCl + HHCl + H22OO ↔↔ HH33OO1+1+ + Cl+ Cl1-1- acidacid basebase c.a. c.b.c.a. c.b. AmphotericAmphoteric – a substance that can– a substance that can act asact as bothboth an acid and base- as water showsan acid and base- as water shows
  36. 36. 3. Lewis Acids and Bases3. Lewis Acids and Bases Gilbert Lewis focused on theGilbert Lewis focused on the donation or acceptance of a pair ofdonation or acceptance of a pair of electrons during a reactionelectrons during a reaction Lewis AcidLewis Acid - electron pair acceptor- electron pair acceptor Lewis BaseLewis Base - electron pair donor- electron pair donor Most general of all 3 definitions;Most general of all 3 definitions; acids don’t even need hydrogen!acids don’t even need hydrogen! SummarySummary: Table 19.4, page 592: Table 19.4, page 592
  37. 37. Gilbert Lewis (1875-1946)Gilbert Lewis (1875-1946)
  38. 38. - Page 593
  39. 39. Section 19.2Section 19.2 Hydrogen Ions and AcidityHydrogen Ions and Acidity OBJECTIVES:OBJECTIVES: –Describe how [H1+ ] and [OH1- ] are related in an aqueous solution.
  40. 40. Section 2Section 2 Hydrogen Ions and AcidityHydrogen Ions and Acidity OBJECTIVES:OBJECTIVES: –Classify a solution as neutral, acidic, or basic given the hydrogen-ion or hydroxide-ion concentration.
  41. 41. Section 19.2Section 19.2 Hydrogen Ions and AcidityHydrogen Ions and Acidity OBJECTIVES:OBJECTIVES: –Convert hydrogen-ion concentrations into pH values and hydroxide-ion concentrations into pOH values.
  42. 42. Section 19.2Section 19.2 Hydrogen Ions and AcidityHydrogen Ions and Acidity OBJECTIVES:OBJECTIVES: –Describe the purpose of an acid-base indicator.
  43. 43. Hydrogen Ions from WaterHydrogen Ions from Water Water ionizes, or falls apart into ions:Water ionizes, or falls apart into ions: H2O ↔ H1+ + OH1- Called the “Called the “self ionizationself ionization” of water” of water Occurs to aOccurs to a very smallvery small extentextent:: [H1+ ] = [OH1- ] = 1 x 10-7 M Since they are equal, aSince they are equal, a neutralneutral solutionsolution results from waterresults from water KKww = [H= [H1+1+ ] x [OH] x [OH1-1- ] = 1 x 10] = 1 x 10-14-14 MM22 KKww is called the “is called the “ion product constantion product constant” for water” for water
  44. 44. Ion Product ConstantIon Product Constant HH22OO ↔↔ HH1+1+ + OH+ OH1-1- KKww isis constantconstant in every aqueous solution:in every aqueous solution: [H[H++ ] x [OH] x [OH-- ] =] = 1 x 101 x 10-14-14 MM22 If [HIf [H++ ] > 10] > 10-7-7 then [OHthen [OH-- ] < 10] < 10-7-7 If [HIf [H++ ] < 10] < 10-7-7 then [OHthen [OH-- ] > 10] > 10-7-7 If we know one, other can be determinedIf we know one, other can be determined If [HIf [H++ ] > 10] > 10-7-7 , it is, it is acidicacidic and [OHand [OH-- ] < 10] < 10-7-7 If [HIf [H++ ] < 10] < 10-7-7 , it is, it is basicbasic and [OHand [OH-- ] > 10] > 10-7-7
  45. 45. - Page 596
  46. 46. The pH concept – from 0 to 14The pH concept – from 0 to 14 pH =pH = pouvoir hydrogenepouvoir hydrogene (Fr.)(Fr.) “hydrogen power”“hydrogen power” definition:definition: pH = -log[HpH = -log[H++ ]] inin neutralneutral pH = -log(1 x 10pH = -log(1 x 10-7-7 )) = 7= 7 inin acidicacidic solution [Hsolution [H++ ] > 10] > 10-7-7 pHpH << -log(10-log(10-7-7 )) – pH < 7 (from 0 to 7 is the acid range) – in base, pH > 7 (7 to 14 is base range)
  47. 47. Calculating pOHCalculating pOH pOH = -log [OHpOH = -log [OH-- ]] [H[H++ ] x [OH] x [OH-- ] = 1 x 10] = 1 x 10-14-14 MM22 pH + pOH = 14pH + pOH = 14 Thus, a solution with a pOHThus, a solution with a pOH less than 7 is basic; with aless than 7 is basic; with a pOH greater than 7 is an acidpOH greater than 7 is an acid Not greatly used like pH is.Not greatly used like pH is.
  48. 48. pH and Significant FigurespH and Significant Figures For pH calculations, the hydrogenFor pH calculations, the hydrogen ion concentration is usuallyion concentration is usually expressed in scientific notationexpressed in scientific notation [H[H1+1+ ] = 0.0010 M = 1.0 x 10] = 0.0010 M = 1.0 x 10-3-3 M, andM, and 0.000.001010 has 2 significant figureshas 2 significant figures the pH = 3.the pH = 3.0000, with the two, with the two numbers to the right of the decimalnumbers to the right of the decimal corresponding to the two significantcorresponding to the two significant figuresfigures
  49. 49. - Page 599
  50. 50. - Page 600
  51. 51. Measuring pHMeasuring pH Why measure pH?Why measure pH? Everyday solutions we use - everything from swimming pools, soil conditions for plants, medical diagnosis, soaps and shampoos, etc. Sometimes we can useSometimes we can use indicatorsindicators, other times, other times we might need awe might need a pHpH metermeter
  52. 52. How to measure pH with wide-range paperHow to measure pH with wide-range paper 1. Moisten the pH indicator paper strip with a few drops of solution, by using a stirring rod. 2.Compare the color to the chart on the vial – then read the pH value.
  53. 53. Some of theSome of the many pHmany pH IndicatorsIndicators and theirand their pH rangepH range
  54. 54. Acid-Base IndicatorsAcid-Base Indicators Although useful, there areAlthough useful, there are limitationslimitations to indicators:to indicators: –usually given for a certain temperature (25 o C), thus may change at different temperatures –what if the solution already has a color, like paint? – the ability of the human eye to distinguish colors is limited
  55. 55. Acid-Base IndicatorsAcid-Base Indicators AA pH meterpH meter may give more definitivemay give more definitive resultsresults –some are large, others portable –works by measuring the voltage between two electrodes; typically accurate to within 0.01 pH unit of the true pH –Instruments need to be calibrated –Fig. 19.15, p.603
  56. 56. Section 3Section 3 Strengths of Acids and BasesStrengths of Acids and Bases OBJECTIVES:OBJECTIVES: –Define strong acids and weak acids.
  57. 57. Section 3Section 3 Strengths of Acids and BasesStrengths of Acids and Bases OBJECTIVES:OBJECTIVES: –Describe how an acid’s strength is related to the value of its acid dissociation constant.
  58. 58. Section 3Section 3 Strengths of Acids and BasesStrengths of Acids and Bases OBJECTIVES:OBJECTIVES: –Calculate an acid dissociation constant (Ka) from concentration and pH measurements.
  59. 59. Section 3Section 3 Strengths of Acids and BasesStrengths of Acids and Bases OBJECTIVES:OBJECTIVES: –Order acids by strength according to their acid dissociation constants (Ka).
  60. 60. Section 3Section 3 Strengths of Acids and BasesStrengths of Acids and Bases OBJECTIVES:OBJECTIVES: –Order bases by strength according to their base dissociation constants (Kb).
  61. 61. StrengthStrength Acids and Bases are classified acordingAcids and Bases are classified acording to the degree to which they ionize into the degree to which they ionize in water:water: –Strong are completely ionized in aqueous solution; this means they ionize 100 % –Weak ionize only slightly in aqueous solution StrengthStrength is very different fromis very different from ConcentrationConcentration
  62. 62. StrengthStrength Strong – means it formsStrong – means it forms manymany ions when dissolved (100 %ions when dissolved (100 % ionization)ionization) Mg(OH)Mg(OH)22 is a strong base- it fallsis a strong base- it falls completely apart (nearly 100%completely apart (nearly 100% when dissolved).when dissolved). –But, not much dissolves- so it is not concentrated
  63. 63. Strong Acid DissociationStrong Acid Dissociation (makes 100 % ions)(makes 100 % ions)
  64. 64. Weak Acid DissociationWeak Acid Dissociation (only partially ionizes)(only partially ionizes)
  65. 65. Measuring strengthMeasuring strength Ionization is reversible:Ionization is reversible: HA + HHA + H22OO ↔↔ HH++ + A+ A-- This makes an equilibriumThis makes an equilibrium Acid dissociation constant = KAcid dissociation constant = Kaa KKaa = [H= [H++ ][A][A-- ]] [HA][HA] Stronger acidStronger acid = more products (ions),= more products (ions), thus athus a larger Klarger Kaa (Table 19.7, page 607)(Table 19.7, page 607) (Note that water is NOT shown, because its concentration is constant, and built into Ka) (Note that the arrow goes both directions.)
  66. 66. What about bases?What about bases? Strong bases dissociate completely.Strong bases dissociate completely. MOH + HMOH + H22OO ↔↔ MM++ + OH+ OH-- (M = a metal)(M = a metal) Base dissociation constant = KBase dissociation constant = Kbb KKbb = [M= [M++ ][OH][OH-- ]] [MOH][MOH] Stronger baseStronger base = more dissociated= more dissociated ions are produced, thus aions are produced, thus a larger Klarger Kbb..
  67. 67. Strength vs. ConcentrationStrength vs. Concentration The wordsThe words concentratedconcentrated andand dilutedilute telltell how much of an acid or base ishow much of an acid or base is dissolved in solution - refers to thedissolved in solution - refers to the number of moles of acid or base in anumber of moles of acid or base in a given volumegiven volume The wordsThe words strongstrong andand weakweak refer to therefer to the extent of ionization of an acid or baseextent of ionization of an acid or base Is aIs a concentrated, weakconcentrated, weak acid possible?acid possible?
  68. 68. PracticePractice Write the KWrite the Kaa expression for HNOexpression for HNO22 1) Equation: HNO2 ↔ H1+ + NO2 1- 2) Ka = [H1+ ] x [NO2 1- ] [HNO2] Write the KWrite the Kbb expression for NHexpression for NH33 (as NH(as NH44OH)OH)
  69. 69. - Page 610
  70. 70. Section 4Section 4 Neutralization ReactionsNeutralization Reactions OBJECTIVES:OBJECTIVES: –Define the products of an acid-base reaction.
  71. 71. Section 4Section 4 Neutralization ReactionsNeutralization Reactions OBJECTIVES:OBJECTIVES: –Explain how acid-base titration is used to calculate the concentration of an acid or a base.
  72. 72. Section 4Section 4 Neutralization ReactionsNeutralization Reactions OBJECTIVES:OBJECTIVES: –Explain the concept of equivalence in neutralization reactions.
  73. 73. Section 4Section 4 Neutralization ReactionsNeutralization Reactions OBJECTIVES:OBJECTIVES: –Describe the relationship between equivalence point and the end point of a titration.
  74. 74. Acid-Base ReactionsAcid-Base Reactions Acid + BaseAcid + Base  Water +Water + SaltSalt Properties related to every day:Properties related to every day: –antacids depend on neutralization –farmers adjust the soil pH –formation of cave stalactites –human body kidney stones from insoluble salts
  75. 75. Acid-Base ReactionsAcid-Base Reactions Neutralization ReactionNeutralization Reaction - a reaction- a reaction in which an acid and a base react inin which an acid and a base react in an aqueous solution to produce aan aqueous solution to produce a salt and water:salt and water: HClHCl(aq)(aq) + NaOH+ NaOH(aq)(aq)  NaClNaCl(aq)(aq) + H+ H22OO(l)(l) HH22SOSO4(aq)4(aq) + 2KOH+ 2KOH(aq)(aq)  KK22SOSO4(aq)4(aq) + 2H+ 2H22OO(l)(l) –Table 19.9, page 613 lists some salts
  76. 76. TitrationTitration TitrationTitration is the process of adding ais the process of adding a known amount of solution of knownknown amount of solution of known concentration to determine theconcentration to determine the concentration of another solutionconcentration of another solution Remember? - aRemember? - a balanced equationbalanced equation isis aa mole ratiomole ratio TheThe equivalence pointequivalence point is when the molesis when the moles of hydrogen ions isof hydrogen ions is equalequal to the molesto the moles of hydroxide ions (= neutralized!)of hydroxide ions (= neutralized!)
  77. 77. - Page 614
  78. 78. TitrationTitration The concentration of acid (or base)The concentration of acid (or base) in solution can be determined byin solution can be determined by performing a neutralization reactionperforming a neutralization reaction –An indicator is used to show when neutralization has occurred –Often we use phenolphthalein- because it is colorless in neutral and acid; turns pink in base
  79. 79. Steps - Neutralization reactionSteps - Neutralization reaction #1. A measured volume of acid of#1. A measured volume of acid of unknown concentration is added tounknown concentration is added to a flaska flask #2. Several drops of indicator added#2. Several drops of indicator added #3. A base of known concentration is#3. A base of known concentration is slowly added, until the indicatorslowly added, until the indicator changes color; measure thechanges color; measure the volumevolume –Figure 19.22, page 615
  80. 80. NeutralizationNeutralization The solution of knownThe solution of known concentration is called theconcentration is called the standard solutionstandard solution –added by using a buret Continue adding until theContinue adding until the indicatorindicator changes colorchanges color –called the “end point” of the titration –Sample Problem 19.7, page 616
  81. 81. Section 5Section 5 Salts in SolutionSalts in Solution OBJECTIVES:OBJECTIVES: –Describe when a solution of a salt is acidic or basic.
  82. 82. Section 5Section 5 Salts in SolutionSalts in Solution OBJECTIVES:OBJECTIVES: –Demonstrate with equations how buffers resist changes in pH.
  83. 83. Salt HydrolysisSalt Hydrolysis AA saltsalt is an ionic compound that:is an ionic compound that: –comes from the anion of an acid –comes from the cation of a base –is formed from a neutralization reaction –some neutral; others acidic or basic ““Salt hydrolysisSalt hydrolysis”” - a- a saltsalt that reactsthat reacts with water to produce an acid or basewith water to produce an acid or base
  84. 84. Salt HydrolysisSalt Hydrolysis Hydrolyzing salts usually come from:Hydrolyzing salts usually come from: 1. a strong acid + a weak base, or 2. a weak acid + a strong base Strong refers to theStrong refers to the degree ofdegree of ionizationionization A strong Acid + a strong Base = Neutral Salt How do youHow do you knowknow if it’s strong?if it’s strong? – Refer to the handout provided (downloadable from my web site)
  85. 85. Salt HydrolysisSalt Hydrolysis To see if the resulting salt isTo see if the resulting salt is acidic or basic, check theacidic or basic, check the “parent” acid and base“parent” acid and base thatthat formed it. Practice on these:formed it. Practice on these: HCl + NaOH H2SO4 + NH4OH CH3COOH + KOH NaCl, a neutral salt (NH4)2SO4, acidic salt CH3COOK, basic salt
  86. 86. BuffersBuffers BuffersBuffers are solutions in which theare solutions in which the pH remains relatively constant,pH remains relatively constant, even when small amounts of acideven when small amounts of acid or base are addedor base are added –made from a pair of chemicals: a weak acid and one of it’s salts; or a weak base and one of it’s salts
  87. 87. BuffersBuffers A buffer system is better able toA buffer system is better able to resist changes in pH than pure waterresist changes in pH than pure water Since it is aSince it is a pairpair of chemicals:of chemicals: –one chemical neutralizes any acid added, while the other chemical would neutralize any additional base –AND, they produce each other in the process!!!
  88. 88. BuffersBuffers Example: Ethanoic (acetic) acidExample: Ethanoic (acetic) acid and sodium ethanoate (alsoand sodium ethanoate (also called sodium acetate)called sodium acetate) Examples on page 621 of theseExamples on page 621 of these TheThe buffer capacitybuffer capacity is theis the amount of acid or base that canamount of acid or base that can be added before a significantbe added before a significant change in pHchange in pH
  89. 89. BuffersBuffers The two buffers that are crucial toThe two buffers that are crucial to maintain the pH of human blood are:maintain the pH of human blood are: 1. carbonic acid (H2CO3) & hydrogen carbonate (HCO3 1- ) 2. dihydrogen phosphate (H2PO4 1- ) & monohydrogen phoshate (HPO4 2- ) –Table 19.10, page 621 has some important buffer systems –Conceptual Problem 19.2, p. 622
  90. 90. Aspirin (which is a type of acid) sometimes causes stomach upset; thus by adding a “buffer”, it does not cause the acid irritation. Bufferin is one brand of a buffered aspirin that is sold in stores. What about the cost compared to plain aspirin?

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