1、ChapterChapterChapter 3 3 3 Fundamentals ofFundamentals ofFundamentals of TitrimetricTitrimetricTitrimetric Analysis Analysis Analysis3.1 General Principles3.2 Standard Solutions3.3 Expressing Concentration of Standard Solutions3.4 Calculations in Titrimetric Analysis202220222022年年年101010月月月5 5 5日日日
2、121212时时时454545分分分3.13.13.1 General PrinciplesGeneral PrinciplesGeneral Principles3.1.1 3.1.1 3.1.1 Some General AspectSome General AspectSome General Aspect In In In a titration,the test substance(a titration,the test substance(a titration,the test substance(analyteanalyteanalyte)reacts with a)reac
3、ts with a)reacts with a reagent added as a solution of known concentration-reagent added as a solution of known concentration-reagent added as a solution of known concentration-referedreferedrefered to as a standard solution,and it is generally added from a to as a standard solution,and it is genera
4、lly added from a to as a standard solution,and it is generally added from a buretburetburet.TheTheThe added solution is called added solution is called added solution is called titranttitranttitrant.The.The.The volume of the volume of the volume of the titranttitranttitrant required just to complete
5、ly required just to completely required just to completely react with the react with the react with the analyteanalyteanalyte is measured.From the is measured.From the is measured.From the required volume and the concentration of the required volume and the concentration of the required volume and t
6、he concentration of the standard solution,the amount of standard solution,the amount of standard solution,the amount of analyteanalyteanalyte can be can be can be calculated.calculated.calculated.The The The analytical techniques of this kind are analytical techniques of this kind are analytical tec
7、hniques of this kind are called titrimetric analysis or volumetric analysis.called titrimetric analysis or volumetric analysis.called titrimetric analysis or volumetric analysis.movingmovingmoving202220222022年年年101010月月月5 5 5日日日121212时时时454545分分分1.1.1.Standard solutionStandard solutionStandard solut
8、ion A A A reagent added as a solution of known reagent added as a solution of known reagent added as a solution of known concentration-concentration-concentration-referedreferedrefered to as a standard solution.to as a standard solution.to as a standard solution.2.2.2.StoichiometricStoichiometricSto
9、ichiometric point(equivalence point)point(equivalence point)point(equivalence point)T T The point at which the he point at which the he point at which the titranttitranttitrant added just added just added just completely reacts with the completely reacts with the completely reacts with the analytean
10、alyteanalyte.3.3.3.End pointEnd pointEnd point T T The point at which the color he point at which the color he point at which the color of the indicator changes and the of the indicator changes and the of the indicator changes and the titration is stopped.titration is stopped.titration is stopped.20
11、2220222022年年年101010月月月5 5 5日日日121212时时时454545分分分4.4.4.IndicatorIndicatorIndicator The material used to The material used to The material used to indicate the end point.indicate the end point.indicate the end point.5.5.5.Titration errorTitration errorTitration error The difference between the end poi
12、nt and the The difference between the end point and the The difference between the end point and the equivalence point.equivalence point.equivalence point.movingmovingmoving202220222022年年年101010月月月5 5 5日日日121212时时时454545分分分3.1.2 3.1.2 3.1.2 Classification of Titration MethodsClassification of Titrat
13、ion MethodsClassification of Titration Methods1.1.1.Acid-base Acid-base Acid-base titrationstitrationstitrations These methods are based on the proton These methods are based on the proton These methods are based on the proton transferring reactions.Both acids and bases can be transferring reactions
14、.Both acids and bases can be transferring reactions.Both acids and bases can be titratedtitratedtitrated.The involved reactions may essentially be.The involved reactions may essentially be.The involved reactions may essentially be expressed as:expressed as:expressed as:H H H+A+A+A-=HA=HA=HA where Aw
15、here Awhere A-is a is a is a BrostedBrostedBrosted base.The base.The base.The titranttitranttitrant used are used are used are generally standard solutions of strong electrolytes,generally standard solutions of strong electrolytes,generally standard solutions of strong electrolytes,such as hydrochlo
16、ric acid and sodium hydroxide.such as hydrochloric acid and sodium hydroxide.such as hydrochloric acid and sodium hydroxide.movingmovingmoving202220222022年年年101010月月月5 5 5日日日121212时时时454545分分分2.2.2.Precipitation Precipitation Precipitation titrationstitrationstitrations Some of the precipitation rea
17、ctions can be used in Some of the precipitation reactions can be used in Some of the precipitation reactions can be used in titrimetric procedures,such astitrimetric procedures,such astitrimetric procedures,such as Ag Ag Ag+X +X +X-=AgXAgXAgX where X where X where X-can be chloride,bromide,iodide or
18、 can be chloride,bromide,iodide or can be chloride,bromide,iodide or thiocyanide(thiocyanide(thiocyanide(-SNC).SNC).SNC).202220222022年年年101010月月月5 5 5日日日121212时时时454545分分分3.3.3.Complexometric titrationsComplexometric titrationsComplexometric titrations The commonly used complexing agent in The commo
19、nly used complexing agent in The commonly used complexing agent in complexometric complexometric complexometric titrationstitrationstitrations is sodium salt of is sodium salt of is sodium salt of ethylenediaminetetraacetic acid(EDTA),which ethylenediaminetetraacetic acid(EDTA),which ethylenediamine
20、tetraacetic acid(EDTA),which reacts with a number of metal ions,forming stable reacts with a number of metal ions,forming stable reacts with a number of metal ions,forming stable complexes:complexes:complexes:MMM2+2+2+Y+Y+Y4-4-4-=MY=MY=MY2-2-2-where M where M where M2+2+2+is the bivalent metal ions,
21、and Y is the bivalent metal ions,and Y is the bivalent metal ions,and Y4-4-4-represents the EDTA anion.represents the EDTA anion.represents the EDTA anion.202220222022年年年101010月月月5 5 5日日日121212时时时454545分分分4.4.4.Oxidation-reduction(Oxidation-reduction(Oxidation-reduction(redoxredoxredox)titrationstit
22、rationstitrations Chemical reactions involving oxidation-reduction Chemical reactions involving oxidation-reduction Chemical reactions involving oxidation-reduction are widely used in titrimetric analysis.For example,are widely used in titrimetric analysis.For example,are widely used in titrimetric
23、analysis.For example,iron,in the+2 oxidation state,can be iron,in the+2 oxidation state,can be iron,in the+2 oxidation state,can be titratedtitratedtitrated with with with standard KMnOstandard KMnOstandard KMnO4 4 4 solution under acidic condition.solution under acidic condition.solution under acid
24、ic condition.2 2 2 MnOMnOMnO4 4 4-+5 C+5 C+5 C2 2 2O O O4 4 42-2-2-+16 H+16 H+16 H+=2 Mn=2 Mn=2 Mn2+2+2+10 CO+10 CO+10 CO2 2 2+8 H+8 H+8 H2 2 2O O O202220222022年年年101010月月月5 5 5日日日121212时时时454545分分分3.1.3 3.1.3 3.1.3 Requirements for Reactions Used Requirements for Reactions Used Requirements for Rea
25、ctions Used ininin Titrimetric Titrimetric Titrimetric Analysis Analysis Analysis1.1.1.The reaction must proceed according to a definite chemical equation The reaction must proceed according to a definite chemical equation The reaction must proceed according to a definite chemical equation without s
26、ide reaction,which means that the reaction follow the definite without side reaction,which means that the reaction follow the definite without side reaction,which means that the reaction follow the definite stoichiometricstoichiometricstoichiometric relationship.relationship.relationship.2.2.2.The r
27、eaction must proceed to virtual completion at the equivalence point.The reaction must proceed to virtual completion at the equivalence point.The reaction must proceed to virtual completion at the equivalence point.The equilibrium constant of the reaction should be very largeThe equilibrium constant
28、of the reaction should be very largeThe equilibrium constant of the reaction should be very large（K K K MYMYMY,high;high;high;K K KSpSpSp low).low).low).The above two will provide a basis for The above two will provide a basis for The above two will provide a basis for stoichiometricstoichiometricst
29、oichiometric calculation.calculation.calculation.3.3.3.Some means must be available for determining when the equivalence Some means must be available for determining when the equivalence Some means must be available for determining when the equivalence point is reached,such as an indicator or some i
30、nstrumental methods to tell point is reached,such as an indicator or some instrumental methods to tell point is reached,such as an indicator or some instrumental methods to tell the end point.the end point.the end point.4.4.4.The reaction should be rapid.The reaction should be rapid.The reaction sho
31、uld be rapid.202220222022年年年101010月月月5 5 5日日日121212时时时454545分分分3.2 3.2 3.2 Standard SolutionsStandard SolutionsStandard SolutionsA standard solution A standard solution A standard solution is a solutionis a solutionis a solution with known concentration;it can with known concentration;it can with kn
32、own concentration;it can sometimes be prepared by sometimes be prepared by sometimes be prepared by dissolving an accurately weighed dissolving an accurately weighed dissolving an accurately weighed quantity of a highly pure material quantity of a highly pure material quantity of a highly pure mater
33、ial called primary standard and called primary standard and called primary standard and diluting to an accurately known diluting to an accurately known diluting to an accurately known volume in a volumetric flask.volume in a volumetric flask.volume in a volumetric flask.202220222022年年年101010月月月5 5 5
34、日日日121212时时时454545分分分A primary standard should fulfill:A primary standard should fulfill:A primary standard should fulfill:(1)(1)(1)It should be It should be It should be sufficiently puresufficiently puresufficiently pure to meet the demand to meet the demand to meet the demand for accuracy in a qu
35、antitative procedure.In general,for accuracy in a quantitative procedure.In general,for accuracy in a quantitative procedure.In general,the total amount of impurities should not exceed 0.01 the total amount of impurities should not exceed 0.01 the total amount of impurities should not exceed 0.01 to
36、 0.02%.to 0.02%.to 0.02%.(2)(2)(2)It should have a It should have a It should have a definite compositiondefinite compositiondefinite composition,just as,just as,just as shown in its formula.shown in its formula.shown in its formula.(3)(3)(3)It should be It should be It should be stablestablestable.
37、The reagent should not be so.The reagent should not be so.The reagent should not be so hygroscopic that it takes up water during weighing hygroscopic that it takes up water during weighing hygroscopic that it takes up water during weighing and should not react with Oand should not react with Oand sh
38、ould not react with O2 2 2 or CO or CO or CO2 2 2.(4)(4)(4)High molar massHigh molar massHigh molar mass in order to minimize the in order to minimize the in order to minimize the consequence of errors in weighing.consequence of errors in weighing.consequence of errors in weighing.202220222022年年年101
39、010月月月5 5 5日日日121212时时时454545分分分n n nOnly a few chemical reagentsOnly a few chemical reagentsOnly a few chemical reagents can meet these can meet these can meet these requirements likerequirements likerequirements like K K K2 2 2CrCrCr2 2 2O O O7 7 7;Na;Na;Na2 2 2C C C2 2 2O O O4 4 4;H;H;H2 2 2C C C
40、2 2 2O O O4 4 4 2H 2H 2H2 2 2O O O NaNaNa2 2 2B B B4 4 4O O O7 7 7 10H 10H 10H2 2 2O;CaCOO;CaCOO;CaCO3 3 3;NaCl NaCl NaCl;Na;Na;Na2 2 2COCOCO3 3 3.n n nMore commonlyMore commonlyMore commonly,a solution with approximately,a solution with approximately,a solution with approximately desired concentrat
41、ion is prepared,then it is desired concentration is prepared,then it is desired concentration is prepared,then it is standardized by standardized by standardized by titratingtitratingtitrating a weighed portion of a a weighed portion of a a weighed portion of a primary standard.primary standard.prim
42、ary standard.n n nFor exampleFor exampleFor example,in acid-base,in acid-base,in acid-base titrationstitrationstitrations,solutions of,solutions of,solutions of hydrochloric acid and sodium hydroxide are so hydrochloric acid and sodium hydroxide are so hydrochloric acid and sodium hydroxide are so p
43、repared,and it is customary to standardize one of prepared,and it is customary to standardize one of prepared,and it is customary to standardize one of them against a secondary standard to obtain the them against a secondary standard to obtain the them against a secondary standard to obtain the conc
44、entration of the other solution.concentration of the other solution.concentration of the other solution.202220222022年年年101010月月月5 5 5日日日121212时时时454545分分分3.3 3.3 3.3 Ways of Expressing Concentration Ways of Expressing Concentration Ways of Expressing Concentration of Standard Solutionof Standard Sol
45、utionof Standard Solution3.3.13.3.13.3.1Concentration of Amount SubstanceConcentration of Amount SubstanceConcentration of Amount Substance the amount of substance in unit volumethe amount of substance in unit volumethe amount of substance in unit volume MolarityMolarityMolarity-a kind of concentrat
46、ion expression.If a kind of concentration expression.If a kind of concentration expression.If n n nB B B moles of moles of moles of substance substance substance B B B are contained in are contained in are contained in V V V liters of solution,the liters of solution,the liters of solution,the concen
47、tration of substance concentration of substance concentration of substance B B B is given by is given by is given by c c cB B B=n n nB B B/V V V,The,The,The commonly usedcommonly usedcommonly used unit is mol/L.unit is mol/L.unit is mol/L.The number of elemental unit of substance The number of eleme
48、ntal unit of substance The number of elemental unit of substance B B B contained in a contained in a contained in a one mole system equals to the atom number contained in 0.012 one mole system equals to the atom number contained in 0.012 one mole system equals to the atom number contained in 0.012 k
49、g of kg of kg of 121212C.C.C.n n nB B B is proportional to the number of elemental unit of is proportional to the number of elemental unit of is proportional to the number of elemental unit of substance substance substance B B B contained in the system(contained in the system(contained in the system
50、(N N NB B B).That is,).That is,).That is,n n nB B B N N NB B B.202220222022年年年101010月月月5 5 5日日日121212时时时454545分分分 When mole is used to express the amount of When mole is used to express the amount of When mole is used to express the amount of substance,substance,substance,the elemental unit must be
