Acid-Base-Equilibria-and-Solubility-Equilibria酸碱平衡与溶解度平衡共28页课件.ppt

1、Acid-Base EquilibriaChapter 17Copyright The McGraw-Hill Companies,Inc.Permission required for reproduction or display.Chapter 17:Acid-Base EquilibriaBuffer CompositionpH of Buffer SolutionspH after small amounts of acid/base addedDesigning Buffer SolutionsAcid-Base TitrationsIndicatorA buffer soluti

2、on is a solution of:A weak acid and its conjugate baseor1.A weak base and it conjugate acid A buffer solution has the ability to resist large changes in pH upon the addition of small amounts of either acid or base.16.3Note:If either the acid or base is a negativeor positive ion;it will be found in t

3、he form of a salt.Note:It is important that the acid and base have the conjugate relationship.Six Strong AcidsHClH2SO4HBrHClO4HIHNO3Which of the following are buffer systems?(a)KF/HF(b)KBr/HBr,(c)Na2CO3/NaHCO3F-is a weak base and HF is its weak conjugate acidbuffer solution(b)HBr is a strong acidnot

4、 a buffer solution(c)CO32-is a weak base and HCO3-is it conjugate acidbuffer solution16.3How a Buffer Withstands Large Changes in pH(CH3COO)H/Na(CH3COO-)Consider an equal molar mixture of CH3COOH and CH3COONaAdd strong acidH+(aq)+CH3COO-(aq)CH3COOH(aq)Add strong baseOH-(aq)+CH3COOH(aq)CH3COO-(aq)+H2

5、O(l)How a Buffer Withstands Large Changes in pH(CH3COO)H/Na(CH3COO-)Base of buffer removes excess H+Acid of buffer removes excess OH-How a Buffer Withstands Large Changes in pH(CH3COO)H/Na(CH3COO-)Introductory Chemistry 2/e by N Tro,Prentice Hall,2019,pg 495A buffer solution is the most effective if

6、.1)there are large amounts of acid/conjugate base2)the amounts of acid and conjugate base are about equalTo find pH of buffer made of;HF/F-HF(aq)H+(aq)+F-(aq)Ka=H+F-HFH+=Ka HF F-If the ratio(HA/A-)stays about same;pH will not change dramatically!A buffer solution is the most effective if.1)there are

7、 large amounts of acid/conjugate base2)the amounts of acid and conjugate base are about equalHFF-Add H+HFF-Add OH-HFF-H+(aq)+F-(aq)HF(aq)Free H+reacts with/removesbase(F-)of buffer and producesmore HF.OH-(aq)+HF(aq)F-(aq)+H2O(l)Free(OH)-reacts with/removesacid(HF)of buffer and producesmore F-.A buff

8、er solution is the most effective if.1)there are large amounts of acid/conjugate base2)the amounts of acid and conjugate base are about equalHFF-Add H+HFF-Add OH-HFF-5000=150005002 =1.000849984998 =0.99950025=157=2.33333=0.42867Determining the pH of Buffer Solutions The calculations are very similar

9、 to determining the pH of weak acid solutions the only difference is that initially there are both some reactants and products present.An easier way to determine pH of Buffer solutionsHenderson-Hasselbalch equationConsider mixture of salt NaA and weak acid HA.HA(aq)H+(aq)+A-(aq)Ka=H+A-HAH+=Ka HAA-lo

10、g H+=-log Ka HAA-pH=pKa+logA-HAHenderson-Hasselbalch equation-log H+=-log Ka-logHAA-conjugate basepH=pKa+logweak acidpH=pKa+logA-HAInsignificant ChangeApproximation is AssumedIn This Equation!What is the pH of a solution containing 0.30 M HCOOH and 0.52 M HCOOK?HCOOH(aq)H+(aq)+HCOO-(aq)Initial(M)Cha

11、nge(M)Equilibrium(M)0.300.00-x+x0.30-x0.52+xx0.52+xCommon ion effect0.30 x 0.300.52+x 0.52pH=pKa+logHCOO-HCOOHHCOOH pKa=3.77pH=3.77+log0.520.30=4.0116.2Mixture of weak acid and conjugate base!=9.20Calculate the pH of the 0.30 M NH3/0.36 M NH4Cl buffer system.What is the pH after the addition of 20.0

12、 mL of 0.050 M NaOH to 80.0 mL of the buffer solution?NH4+(aq)H+(aq)+NH3(aq)pH=pKa+logNH3NH4+pKa=9.25pH=9.25+log0.300.36=9.17NH4+(aq)+OH-(aq)H2O(l)+NH3(aq)start(moles)end(moles)0.0290.0010.0240.0280.00.025pH=9.25+log0.250.28NH4+=0.0280.10final volume=80.0 mL+20.0 mL=100 mLNH3=0.0250.1016.3Designing

13、Buffer SolutionspH=pKa+log X-/HX Buffers are most effective if there are equal and large amounts of weak acid and conjugate base.X-=HX pH=pKa+log(1)pH=pKapKa of Weak AcidsWeak AcidpKaHydrofluoric Acid3.15Benzoic Acid4.19Carbonic Acid6.38Hydrocyanic Acid9.31TitrationsIn a titration a solution of accu

14、rately known concentration is added gradually added to another solution of unknown concentration until the chemical reaction between the two solutions is complete.Equivalence point the point at which the reaction is completeIndicator substance that changes color at(or near)the equivalence point Slow

15、ly add baseto unknown acidUNTILThe indicatorchanges color(pink)4.7Acid-Base TitrationsIntroductory Chemistry 2/e by N Tro,Prentice Hall,2019,pg 480At endpoint/equivalence pointmoles H+=moles(OH)-MV(acid)=MV(base)Two ways to get endpoint/equivalence pointColor changeMid-point of steep rise of acid/ba

16、se titration curveStrong Acid-Strong Base TitrationsNaOH(aq)+HCl(aq)H2O(l)+NaCl(aq)0.10 M NaOH added to 25 mL of 0.10 M HCl16.4neutral saltWeak Acid-Strong Base TitrationsCH3COOH(aq)+NaOH(aq)CH3COONa(aq)+H2O(l)At equivalence point(pH 7):16.4Basic SaltStrong Acid-Weak Base TitrationsHCl(aq)+NH3(aq)NH4Cl(aq)At equivalence point(pH 7Use cresol red or phenolphthalein16.5