单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,Chapter,3,Fundamentals of Titrimetric Analysis,3.1,General Principles,3.2,Standard Solutions,3.3,Expressing Concentration,of Standard Solutions,3.4,Calculations in Titrimetric,Analysis,2024/11/18,Chapter 3 Fundamentals of Tit,1,3.1,General Principles,3.1.1,Some General Aspect,In,a titration,the test substance(analyte)reacts with a reagent added as a solution of known concentration-refered to as a standard solution,and it is generally added from a buret.,The,added solution is called titrant.The volume of the titrant required just to completely react with the analyte is measured.From the required volume and the concentration of the standard solution,the amount of analyte can be calculated.,The,analytical techniques of this kind are called titrimetric analysis or volumetric analysis.,moving,2024/11/18,3.1 General Principles3.1.1,1.,Standard solution,A,reagent added as a solution of known concentration-refered to as a standard solution.,2.,Stoichiometric point(equivalence point),T,he point at which the titrant added just completely reacts with the analyte.,3.,End point,T,he point at which the color of the indicator changes and the titration is stopped.,2024/11/18,1.Standard solution A reag,4.,Indicator,The material used to indicate the end point.,5.,Titration error,The difference between the end point and the equivalence point.,moving,2024/11/18,4.Indicator The material u,3.1.2,Classification of Titration Methods,1.,Acid-base titrations,These methods are based on the proton transferring reactions.Both acids and bases can be titrated.The involved reactions may essentially be expressed as:,H,+,+A,-,=HA,where A,-,is a Brosted base.The titrant used are generally standard solutions of strong electrolytes,such as hydrochloric acid and sodium hydroxide.,moving,2024/11/18,3.1.2 Classification of Titr,2.,Precipitation titrations,Some of the precipitation reactions can be used in titrimetric procedures,such as,Ag,+,+X,-,=AgX,where X,-,can be chloride,bromide,iodide or thiocyanide(,-,SNC).,2024/11/18,2.Precipitation titrations,3.,Complexometric titrations,The commonly used complexing agent in complexometric titrations is sodium salt of ethylenediaminetetraacetic acid(EDTA),which reacts with a number of metal ions,forming stable complexes:,M,2+,+Y,4-,=MY,2-,where M,2+,is the bivalent metal ions,and Y,4-,represents the EDTA anion.,2024/11/18,3.Complexometric titrations,4.,Oxidation-reduction(redox)titrations,Chemical reactions involving oxidation-reduction are widely used in titrimetric analysis.For example,iron,in the+2 oxidation state,can be titrated with standard KMnO,4,solution under acidic condition.,2,MnO,4,-,+5 C,2,O,4,2-,+16 H,+,=2 Mn,2+,+10 CO,2,+8 H,2,O,2024/11/18,4.Oxidation-reduction(redox),3.1.3,Requirements for Reactions Used in Titrimetric Analysis,1.,The reaction must proceed according to a definite chemical equation without side reaction,which means that the reaction follow the definite stoichiometric relationship.,2.,The reaction must proceed to virtual completion at the equivalence point.The equilibrium constant of the reaction should be very large,（,K,MY,high;,K,Sp,low).,The above two will provide a basis for stoichiometric calculation.,3.,Some means must be available for determining when the equivalence point is reached,such as an indicator or some instrumental methods to tell the end point.,4.,The reaction should be rapid.,2024/11/18,3.1.3 Requirements for Reacti,3.2,Standard Solutions,A standard solution,is a solution,with known concentration;it can sometimes be prepared by dissolving an accurately weighed quantity of a highly pure material called primary standard and diluting to an accurately known volume in a volumetric flask.,2024/11/18,3.2 Standard SolutionsA stand,A primary standard should fulfill:,(1),It should be,sufficiently pure,to meet the demand for accuracy in a quantitative procedure.In general,the total amount of impurities should not exceed 0.01 to 0.02%.,(2),It should have a,definite composition,just as shown in its formula.,(3),It should be,stable,.The reagent should not be so hygroscopic that it takes up water during weighing and should not react with O,2,or CO,2,.,(4),High molar mass,in order to minimize the consequence of errors in weighing.,2024/11/18,A primary standard should fulf,Only a few chemical reagents,can meet these requirements like,K,2,Cr,2,O,7,;Na,2,C,2,O,4,;H,2,C,2,O,4,2H,2,O Na,2,B,4,O,7,10H,2,O;CaCO,3,;NaCl;Na,2,CO,3,.,More commonly,a solution with approximately desired concentration is prepared,then it is standardized by titrating a weighed portion of a primary standard.,For example,in acid-base titrations,solutions of hydrochloric acid and sodium hydroxide are so prepared,and it is customary to standardize one of them against a secondary standard to obtain the concentration of the other solution.,2024/11/18,Only a few chemical reagents c,3.3,Ways of Expressing Concentration of Standard Solution,3.3.1,Concentration of Amo