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1、Copyright Cengage Learning.All rights reserved,2,Models of Acids and Bases,Arrhenius:Acids produce H+ions in solution,bases produce OH-ions.BrnstedLowry:Acids are proton(H+)donors,bases are proton acceptors.HCl+H2O Cl-+H3O+acid base,BrnstedLowry Reaction,Copyright Cengage Learning.All rights reserve
2、d,3,Copyright Cengage Learning.All rights reserved,4,Acid in Water,HA(aq)+H2O(l)H3O+(aq)+A-(aq)Conjugate base is everything that remains of the acid molecule after a proton is lost.Conjugate acid is formed when the proton is transferred to the base.,Acid Ionization Equilibrium,Copyright Cengage Lear
3、ning.All rights reserved,5,Strong acid:Ionization equilibrium lies far to the right.Yields a weak conjugate base.Weak acid:Ionization equilibrium lies far to the left.Weaker the acid,stronger its conjugate base.,Copyright Cengage Learning.All rights reserved,6,Copyright Cengage Learning.All rights r
4、eserved,7,Various Ways to Describe Acid Strength,Copyright Cengage Learning.All rights reserved,8,Water as an Acid and a Base,Water is amphoteric:Behaves either as an acid or as a base.At 25C:Kw=H+OH=1.0 1014No matter what the solution contains,the product of H+and OH must always equal 1.0 1014 at 2
5、5C.,Copyright Cengage Learning.All rights reserved,9,Three Possible Situations,H+=OH;neutral solutionH+OH;acidic solutionOH H+;basic solution,Copyright Cengage Learning.All rights reserved,10,Self-Ionization of Water,Copyright Cengage Learning.All rights reserved,11,HA(aq)+H2O(l)H3O+(aq)+A-(aq)acid
6、base conjugate conjugate acid baseWhat is the equilibrium constant expression for an acid acting in water?,Copyright Cengage Learning.All rights reserved,12,CONCEPT CHECK!,If the equilibrium lies to the right,the value for Ka is _.large(or 1)If the equilibrium lies to the left,the value for Ka is _.
7、small(or 1),Copyright Cengage Learning.All rights reserved,13,CONCEPT CHECK!,HA(aq)+H2O(l)H3O+(aq)+A(aq)If water is a better base than A,do products or reactants dominate at equilibrium?Does this mean HA is a strong or weak acid?Is the value for Ka greater or less than 1?,Copyright Cengage Learning.
8、All rights reserved,14,CONCEPT CHECK!,Consider a 1.0 M solution of HCl.Order the following from strongest to weakest base and explain:H2O(l)A(aq)(from weak acid HA)Cl(aq),Copyright Cengage Learning.All rights reserved,15,CONCEPT CHECK!,Lets Think About It,How good is Cl(aq)as a base?Is A(aq)a good b
9、ase?The bases from strongest to weakest are:A,H2O,Cl,Copyright Cengage Learning.All rights reserved,16,Consider a solution of NaA where A is the anion from weak acid HA:A(aq)+H2O(l)HA(aq)+OH(aq)base acid conjugate conjugate acid baseWhich way will equilibrium lie?left,Copyright Cengage Learning.All
10、rights reserved,17,CONCEPT CHECK!,Consider a solution of NaA where A is the anion from weak acid HA:A(aq)+H2O(l)HA(aq)+OH(aq)base acid conjugate conjugate acid baseb)Is the value for Kb greater than or less than 1?less than 1,Copyright Cengage Learning.All rights reserved,18,CONCEPT CHECK!,Consider
11、a solution of NaA where A is the anion from weak acid HA:A(aq)+H2O(l)HA(aq)+OH(aq)base acid conjugate conjugate acid basec)Does this mean A is a strong or weak base?strong base,Copyright Cengage Learning.All rights reserved,19,CONCEPT CHECK!,Acetic acid(HC2H3O2)and HCN are both weak acids.Acetic aci
12、d is a stronger acid than HCN.Arrange these bases from weakest to strongest and explain your answer:H2O Cl CN C2H3O2,Copyright Cengage Learning.All rights reserved,20,CONCEPT CHECK!,Lets Think About It,H2O(l)+H2O(l)H3O+(aq)+OH(aq)acid base conjugate conjugate acid baseAt 25C,Kw=1.0 1014The bases fro
13、m weakest to strongest are:Cl,H2O,C2H3O2,CN,Copyright Cengage Learning.All rights reserved,21,Discuss whether the value of K for the reaction:HCN(aq)+F(aq)CN(aq)+HF(aq)is 11=1(Ka for HCN is 6.21010;Ka for HF is 7.2104.)Explain your answer.,Copyright Cengage Learning.All rights reserved,22,CONCEPT CH
14、ECK!,Calculate the value for K for the reaction:HCN(aq)+F(aq)CN(aq)+HF(aq)(Ka for HCN is 6.21010;Ka for HF is 7.2104.)K=8.6 107,Copyright Cengage Learning.All rights reserved,23,CONCEPT CHECK!,pH=logH+pH changes by 1 for every power of 10 change in H+.A compact way to represent solution acidity.pH d
15、ecreases as H+increases.Significant figures:The number of decimal places in the log is equal to the number of significant figures in the original number.,Copyright Cengage Learning.All rights reserved,24,pH Range,pH=7;neutralpH 7;basicHigher the pH,more basic.pH 7;acidicLower the pH,more acidic.,Cop
16、yright Cengage Learning.All rights reserved,25,The pH Scale and pH Values of Some Common Substances,Copyright Cengage Learning.All rights reserved,26,Calculate the pH for each of the following solutions.1.0 104 M H+pH=4.00b)0.040 M OH pH=12.60,Copyright Cengage Learning.All rights reserved,27,EXERCI
17、SE!,The pH of a solution is 5.85.What is the H+for this solution?H+=1.4 106 M,Copyright Cengage Learning.All rights reserved,28,EXERCISE!,pH and pOH,Recall:Kw=H+OHlog Kw=logH+logOHpKw=pH+pOH14.00=pH+pOH,Copyright Cengage Learning.All rights reserved,29,Calculate the pOH for each of the following sol
18、utions.1.0 104 M H+pOH=10.00b)0.040 M OH pOH=1.40,Copyright Cengage Learning.All rights reserved,30,EXERCISE!,The pH of a solution is 5.85.What is the OH for this solution?OH=7.1 109 M,Copyright Cengage Learning.All rights reserved,31,EXERCISE!,Thinking About AcidBase Problems,What are the major spe
19、cies in solution?What is the dominant reaction that will take place?Is it an equilibrium reaction or a reaction that will go essentially to completion?React all major species until you are left with an equilibrium reaction.Solve for the pH if needed.,Copyright Cengage Learning.All rights reserved,32
20、,Consider an aqueous solution of 2.0 103 M HCl.What are the major species in solution?H+,Cl,H2OWhat is the pH?pH=2.70,Copyright Cengage Learning.All rights reserved,33,CONCEPT CHECK!,Calculate the pH of a 1.5 1011 M solution of HCl.pH=7.00,Copyright Cengage Learning.All rights reserved,34,CONCEPT CH
21、ECK!,Calculate the pH of a 1.5 102 M solution of HNO3.,Copyright Cengage Learning.All rights reserved,35,CONCEPT CHECK!,Lets Think About It,When HNO3 is added to water,a reaction takes place immediately:HNO3+H2O H3O+NO3,Copyright Cengage Learning.All rights reserved,36,Lets Think About It,Why is thi
22、s reaction not likely?NO3(aq)+H2O(l)HNO3(aq)+OH(aq),Copyright Cengage Learning.All rights reserved,37,Lets Think About It,What reaction controls the pH?H2O(l)+H2O(l)H3O+(aq)+OH(aq)In aqueous solutions,this reaction is always taking place.But is water the major contributor of H+(H3O+)?pH=1.82,Copyrig
23、ht Cengage Learning.All rights reserved,38,Solving Weak Acid Equilibrium Problems,List the major species in the solution.Choose the species that can produce H+,and write balanced equations for the reactions producing H+.Using the values of the equilibrium constants for the reactions you have written
24、,decide which equilibrium will dominate in producing H+.Write the equilibrium expression for the dominant equilibrium.,Copyright Cengage Learning.All rights reserved,39,Solving Weak Acid Equilibrium Problems,List the initial concentrations of the species participating in the dominant equilibrium.Def
25、ine the change needed to achieve equilibrium;that is,define x.Write the equilibrium concentrations in terms of x.Substitute the equilibrium concentrations into the equilibrium expression.,Copyright Cengage Learning.All rights reserved,40,Solving Weak Acid Equilibrium Problems,Solve for x the“easy”wa
26、y,that is,by assuming that HA0 x about equals HA0.Use the 5%rule to verify whether the approximation is valid.Calculate H+and pH.,Copyright Cengage Learning.All rights reserved,41,Consider a 0.80 M aqueous solution of the weak acid HCN(Ka=6.2 1010).What are the major species in solution?HCN,H2O,Copy
27、right Cengage Learning.All rights reserved,42,CONCEPT CHECK!,Lets Think About It,Why arent H+or CN major species?,Copyright Cengage Learning.All rights reserved,43,Consider This,HCN(aq)+H2O(l)H3O+(aq)+CN(aq)Ka=6.2 10-10H2O(l)+H2O(l)H3O+(aq)+OH(aq)Kw=1.0 10-14Which reaction controls the pH?Explain.,C
28、opyright Cengage Learning.All rights reserved,44,Calculate the pH of a 0.50 M aqueous solution of the weak acid HF.(Ka=7.2 104),Copyright Cengage Learning.All rights reserved,45,EXERCISE!,Lets Think About It,What are the major species in solution?HF,H2OWhy arent H+and F major species?,Copyright Ceng
29、age Learning.All rights reserved,46,Lets Think About It,What are the possibilities for the dominant reaction?HF(aq)+H2O(l)H3O+(aq)+F(aq)Ka=7.2 10-4 H2O(l)+H2O(l)H3O+(aq)+OH(aq)Kw=1.0 10-14Which reaction controls the pH?Why?,Copyright Cengage Learning.All rights reserved,47,Steps Toward Solving for p
30、H,Ka=7.2 104pH=1.72,Copyright Cengage Learning.All rights reserved,48,Percent Dissociation(Ionization),For a given weak acid,the percent dissociation increases as the acid becomes more dilute.,Copyright Cengage Learning.All rights reserved,49,A solution of 8.00 M formic acid(HCHO2)is 0.47%ionized in
31、 water.Calculate the Ka value for formic acid.Ka=1.8 104,Copyright Cengage Learning.All rights reserved,50,EXERCISE!,Calculate the pH of an 8.00 M solution of formic acid.Use the data from the previous slide to help you solve this problem.pH=1.42,Copyright Cengage Learning.All rights reserved,51,EXE
32、RCISE!,The value of Ka for a 4.00 M formic acid solution should be:higher than lower thanthe same as the value of Ka of an 8.00 M formic acid solution.Explain.,Copyright Cengage Learning.All rights reserved,52,EXERCISE!,The percent ionization of a 4.00 M formic acid solution should be:higher than lo
33、wer thanthe same as the percent ionization of an 8.00 M formic acid solution.Explain.,Copyright Cengage Learning.All rights reserved,53,CONCEPT CHECK!,The pH of a 4.00 M formic acid solution should be:higher than lower thanthe same as the pH of an 8.00 M formic acid solution.Explain.,Copyright Cenga
34、ge Learning.All rights reserved,54,CONCEPT CHECK!,Calculate the percent ionization of a 4.00 M formic acid solution in water.%Ionization=0.67%,Copyright Cengage Learning.All rights reserved,55,EXERCISE!,Calculate the pH of a 4.00 M solution of formic acid.pH=1.57,Copyright Cengage Learning.All right
35、s reserved,56,EXERCISE!,Arrhenius:bases produce OH ions.BrnstedLowry:bases are proton acceptors.In a basic solution at 25C,pH 7.Ionic compounds containing OH-are generally considered strong bases.LiOH,NaOH,KOH,Ca(OH)2pOH=logOH pH=14.00 pOH,Copyright Cengage Learning.All rights reserved,57,Calculate
36、the pH of a 1.0 103 M solution of sodium hydroxide.pH=11.00,Copyright Cengage Learning.All rights reserved,58,CONCEPT CHECK!,Calculate the pH of a 1.0 103 M solution of calcium hydroxide.pH=11.30,Copyright Cengage Learning.All rights reserved,59,CONCEPT CHECK!,Equilibrium expression for weak bases u
37、ses Kb.CN(aq)+H2O(l)HCN(aq)+OH(aq),Copyright Cengage Learning.All rights reserved,60,pH calculations for solutions of weak bases are very similar to those for weak acids.Kw=H+OH=1.0 1014pOH=logOH pH=14.00 pOH,Copyright Cengage Learning.All rights reserved,61,Calculate the pH of a 2.0 M solution of a
38、mmonia(NH3).(Kb=1.8 105)pH=11.78,Copyright Cengage Learning.All rights reserved,62,CONCEPT CHECK!,Acids that can furnish more than one proton.Always dissociates in a stepwise manner,one proton at a time.The conjugate base of the first dissociation equilibrium becomes the acid in the second step.For
39、a typical weak polyprotic acid:Ka1 Ka2 Ka3For a typical polyprotic acid in water,only the first dissociation step is important to pH.,Copyright Cengage Learning.All rights reserved,63,Calculate the pH of a 1.00 M solution of H3PO4.Ka1=7.5 10-3Ka2=6.2 10-8Ka3=4.8 10-13 pH=1.08,Copyright Cengage Learn
40、ing.All rights reserved,64,EXERCISE!,Calculate the equilibrium concentration of PO43-in a 1.00 M solution of H3PO4.Ka1=7.5 10-3Ka2=6.2 10-8Ka3=4.8 10-13PO43-=3.6 10-19 M,Copyright Cengage Learning.All rights reserved,65,CONCEPT CHECK!,Salts,Ionic compounds.When dissolved in water,break up into its i
41、ons(which can behave as acids or bases).,Copyright Cengage Learning.All rights reserved,66,Salts,The salt of a strong acid and a strong base gives a neutral solution.KCl,NaNO3,Copyright Cengage Learning.All rights reserved,67,Salts,A basic solution is formed if the anion of the salt is the conjugate
42、 base of a weak acid.NaF,KC2H3O2Kw=Ka KbUse Kb when starting with base.,Copyright Cengage Learning.All rights reserved,68,Salts,An acidic solution is formed if the cation of the salt is the conjugate acid of a weak base.NH4ClKw=Ka KbUse Ka when starting with acid.,Copyright Cengage Learning.All righ
43、ts reserved,69,Copyright Cengage Learning.All rights reserved,70,Qualitative Prediction of pH of Salt Solutions(from Weak Parents),Copyright Cengage Learning.All rights reserved,71,HC2H3O2 Ka=1.8 10-5 HCN Ka=6.2 10-10Calculate the Kb values for:C2H3O2 and CNKb(C2H3O2-)=5.6 10-10Kb(CN-)=1.6 10-5,Copy
44、right Cengage Learning.All rights reserved,EXERCISE!,Arrange the following 1.0 M solutions from lowest to highest pH.HBr NaOH NH4Cl NaCN NH3 HCN NaCl HFJustify your answer.HBr,HF,HCN,NH4Cl,NaCl,NaCN,NH3,NaOH,Copyright Cengage Learning.All rights reserved,73,CONCEPT CHECK!,Consider a 0.30 M solution
45、of NaF.The Ka for HF is 7.2 10-4.What are the major species?Na+,F-,H2O,Copyright Cengage Learning.All rights reserved,74,CONCEPT CHECK!,Lets Think About It,Why isnt NaF considered a major species?What are the possibilities for the dominant reactions?,Copyright Cengage Learning.All rights reserved,75
46、,Lets Think About It,The possibilities for the dominant reactions are:F(aq)+H2O(l)HF(aq)+OH(aq)H2O(l)+H2O(l)H3O+(aq)+OH(aq)Na+(aq)+H2O(l)NaOH+H+(aq)Na+(aq)+F(aq)NaF,Copyright Cengage Learning.All rights reserved,76,Lets Think About It,How do we decide which reaction controls the pH?F(aq)+H2O(l)HF(aq
47、)+OH(aq)H2O(l)+H2O(l)H3O+(aq)+OH(aq)Determine the equilibrium constant for each reaction.,Copyright Cengage Learning.All rights reserved,77,Calculate the pH of a 0.75 M aqueous solution of NaCN.Ka for HCN is 6.2 1010.,Copyright Cengage Learning.All rights reserved,78,EXERCISE!,Lets Think About It,Wh
48、at are the major species in solution?Na+,CN,H2OWhy isnt NaCN considered a major species?,Copyright Cengage Learning.All rights reserved,79,Lets Think About It,What are all possibilities for the dominant reaction?The possibilities for the dominant reaction are:CN(aq)+H2O(l)HCN(aq)+OH(aq)H2O(l)+H2O(l)
49、H3O+(aq)+OH(aq)Na+(aq)+H2O(l)NaOH+H+(aq)Na+(aq)+CN(aq)NaCNWhich of these reactions really occur?,Copyright Cengage Learning.All rights reserved,80,Lets Think About It,How do we decide which reaction controls the pH?CN(aq)+H2O(l)HCN(aq)+OH(aq)H2O(l)+H2O(l)H3O+(aq)+OH(aq),Copyright Cengage Learning.Al
50、l rights reserved,81,Steps Toward Solving for pH,Kb=1.6 105 pH=11.54,Models of Acids and Bases,Two factors for acidity in binary compounds:Bond Polarity(high is good)Bond Strength(low is good),Copyright Cengage Learning.All rights reserved,83,Bond Strengths and Acid Strengths for Hydrogen Halides,Co
