ch17---acid-base-equilibrium-I.ppt

5/21/20245/21/20245/21/20245/21/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 21Chapter 17Acid-base Equilibrium I:The Basic Concepts17.1 Concept of Acid and Base 17.2 Dissociation of Water17.3 The pH Scale 17.4 Strength of Acids and Bases5/21/20245/21/20245/21/20245/21/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 2217.1 Concept of Acid and Base(SB p.128)Arrhenius Acid-base TheoryArrhenius Acid-base Theory suggested that 1)An acid is a substance which ionizes to give hydrogen ions(H+)and its corresponding negative ions when dissolved in water2)e.g.HCl(g)H2O H+(aq)+Cl-(aq)2)A base is a substance which gives hydroxide ions(OH-)and its corresponding positive ions when dissolved in water.3)e.g.NaOH(s)H2O Na+(aq)+OH-(aq)5/21/20245/21/20245/21/20245/21/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 23Acid -a proton(H+)donorBase-a proton(H+)acceptoracidbase17.1 Concept of Acid and Base(SB p.130)Bronsted-Lowry Acid-base TheoryHCl(aq)+H2O(l)H3O+(aq)+Cl-(aq)5/21/20245/21/20245/21/20245/21/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 24Acid -a proton(H+)donorBase-a proton(H+)acceptoracidbaseBronsted-Lowry Acid-base TheoryHCl(aq)+H2O(l)H3O+(aq)+Cl-(aq)17.1 Concept of Acid and Base(SB p.130)5/21/20245/21/20245/21/20245/21/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 25Acid -a proton(H+)donorBase-a proton(H+)acceptoracidbaseacidbase17.1 Concept of Acid and Base(SB p.131)Bronsted-Lowry Acid-base TheoryHCl(aq)+H2O(l)H3O+(aq)+Cl-(aq)5/21/20245/21/20245/21/20245/21/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 26acidbaseacidbaseconjugateacidconjugatebaseCl-is the conjugate base of the acid HCl.H3O+is the conjugate acid of the base H2O.17.1 Concept of Acid and Base(SB p.131)Bronsted-Lowry Acid-base TheoryHCl(aq)+H2O(l)H3O+(aq)+Cl-(aq)5/21/20245/21/20245/21/20245/21/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 27Other examples of conjugate acid-base pairsacidbaseconjugateacidconjugatebaseacidbaseconjugateacidconjugatebase17.1 Concept of Acid and Base(SB p.132)CH3COOH(aq)+H2O(l)H3O+(aq)+CH3COO-(aq)H2SO4(aq)+H2O(l)H3O+(aq)+HSO4-(aq)5/21/20245/21/20245/21/20245/21/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 28Other examples of conjugate acid-base pairsacidbaseconjugateacidconjugatebaseacidbaseconjugateacidconjugatebase17.1 Concept of Acid and Base(SB p.132)H2CO3(aq)+H2O(l)H3O+(aq)+HCO3-(aq)NH3(aq)+H2O(l)NH4+(aq)+OH-(aq)5/21/20245/21/20245/21/20245/21/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 29 Dissociation of WaterH2O(l)+H2O(l)H3O+(aq)+OH-(aq)Note that H2O(l)remains nearly constant.Thus we have:ionic product of waterDo you think Kw varies with temp?17.2 Dissociation of Water(SB p.133)Kw=H3O+(aq)OH-(aq)Or 2H2O(l)H3O+(aq)+OH-(aq)Kc=This equation holds for any aqueous solution.5/21/20245/21/20245/21/20245/21/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 210Dissociation of WaterThus the ionic product is represented as:Sometimes the above equation is simplified as:Kw=H+(aq)OH-(aq)H+Bare H+cannot exist in solution(charge/size )H(H2O)5+(solvated H3O+)H3O+(stabilized)17.2 Dissociation of Water(SB p.133)2H2O(l)H3O+(aq)+OH-(aq)H2O(l)H+(aq)+OH-(aq)5/21/20245/21/20245/21/20245/21/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 211The pH ScaleFor pure water at 250C,17.3 The pH Scale(SB p.134)pH=-logH3O+(aq)pOH=-logOH-(aq)At 25oC,H3O+(aq)=OH-(aq)=1 x 10-7 mol dm-3 pH=-log H3O+(aq)=-log(1 x 10-7)=75/21/20245/21/20245/21/20245/21/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 21217.3 The pH Scale(SB p.134)pH=-logH3O+(aq)pOH=-logOH-(aq)For acidic solutions at 25oC,H3O+(aq)OH-(aq)H3O+(aq)1 x 10-7 mol dm-3-log H3O+(aq)7 pH 75/21/20245/21/20245/21/20245/21/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 213pH=-logH3O+(aq)pOH=-logOH-(aq)For alkaline solutions at 25oC,H3O+(aq)OH-(aq)H3O+(aq)7 pH 717.3 The pH Scale(SB p.134)5/21/20245/21/20245/21/20245/21/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 21417.3 The pH Scale(SB p.135)5/21/20245/21/20245/21/20245/21/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 215Universal IndicatorUniversal indicator is a mixture of dyes which shows different colours at different pH.pH paper is a piece of filter paper soaked with universal indicator.17.3 The pH Scale(SB p.136)Measurement of pH5/21/20245/21/20245/21/20245/21/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 216pH meterpH meter is an instrument which can measure the pH values of solutions directly.The meter is connected to a glass electrode which is sensitive to H3O+together with a reference electrode.Measurement of pH17.3 The pH Scale(SB p.136)5/21/20245/21/20245/21/20245/21/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 217H2O(l)remains nearly constant.Dissociation constant17.4 Strength of Acids and Bases(SB p.138)Strong and Weak AcidsHA(aq)+H2O(l)H3O+(aq)+A-(aq)Kc=Ka=5/21/20245/21/20245/21/20245/21/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 218Remarks1.Ka is an equilibrium constant and is independent of concentration.Thus it can be used to describe the strength of the acid.(Note that pH varies with concentration.)17.4 Strength of Acids and Bases(SB p.138)2.Sometimes the Ka expression is simplified as follows:HA(aq)H+(aq)+A-(aq)Ka=5/21/20245/21/20245/21/20245/21/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 21917.4 Strength of Acids and Bases(SB p.139)5/21/20245/21/20245/21/20245/21/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 220pKa ValuespKa=-log KapKa strength of acid 17.4 Strength of Acids and Bases(SB p.139)AcidKa(mol dm-3)pKaRelative strengthHIHBrHNO3Citric acidH2O 3 x 1091 x 109287.5 x 10-51.8 x 10-16-9.48-9.00-1.454.1215.74Very strongVery strongStrongWeakVery weak5/21/20245/21/20245/21/20245/21/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 221H2O(l)remains nearly constant.Dissociation constant17.4 Strength of Acids and Bases(SB p.140)Strong and Weak BasesB(aq)+H2O(l)HB+(aq)+OH-(aq)Kb=5/21/20245/21/20245/21/20245/21/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 222pKb=-log KbpKb strength of base17.4 Strength of Acids and Bases(SB p.140)BaseKb(mol dm-3)pKbRelative strength(C2H5)2NHNH3C6H5NH29.55 x 10-41.74 x 10-54.27 x 10-103.024.769.37weakweakweakStrong and Weak Bases5/21/20245/21/20245/21/20245/21/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 22317.4 Strength of Acids and Bases(SB p.146)Polyprotic AcidsH2CO3(aq)+H2O(l)H3O+(aq)+HCO3-(aq)HCO3-(aq)+H2O(l)H3O+(aq)+CO32-(aq)H2CO3(aq)+2H2O(l)2H3O+(aq)+CO32-(aq)Ka=x5/21/20245/21/20245/21/20245/21/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 224RemarksEach successive dissociation constant is smaller than the previous one.(Increased difficulty of removing an hydrogen ion from the more negative species.)H2A =H+HA-HA-=H+A2-Ka1Ka217.4 Strength of Acids and Bases(SB p.147)AcidKa1(mol dm-3)Ka2(mol dm-3)Ka3(mol dm-3)Carbonic acid(H2CO3(aq)Selenious acid(H2SeO3(aq)Phosphoric acid(H3PO4(aq)4.5 x 10-73.0 x 10-31.1 x 10-24.7 x 10-115.0 x10-87.5 x 10-8-4.8 x 10-135/21/20245/21/20245/21/20245/21/2024H+H+H+OH-OH-OH-New Way Chemistry for Hong Kong A-Level Book 225