1、chapter03-Fundamentals-of-Titrimetric-Analysis分析化学课件3.1 General Principles3.1.1 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 i
2、s 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 volumetr
3、ic analysis.2022-10-51.Standard solution A reagent added as a solution of known concentration-refered to as a standard solution.2.Stoichiometric point(equivalence point)The point at which the titrant added just completely reacts with the analyte.3.End point The point at which the color of the indica
4、tor changes and the titration is stopped.2022-10-54.Indicator The material used to indicate the end point.5.Titration error The difference between the end point and the equivalence point.2022-10-53.1.2 Classification of Titration Methods2022-10-52.Precipitation titrations2022-10-53.Complexometric ti
5、trations2022-10-54.Oxidation-reduction(redox)titrations2022-10-53.1.3 Requirements for Reactions Used in Titrimetric Analysis2022-10-53.2 Standard Solutions2022-10-5A primary standard should fulfill:2022-10-5nOnly a few chemical reagents can meet these requirements like K2Cr2O7;Na2C2O4;H2C2O4 2H2O N
6、a2B4O7 10H2O;CaCO3;NaCl;Na2CO3.nMore commonly,a solution with approximately desired concentration is prepared,then it is standardized by titrating a weighed portion of a primary standard.nFor example,in acid-base titrations,solutions of hydrochloric acid and sodium hydroxide are so prepared,and it i
7、s customary to standardize one of them against a secondary standard to obtain the concentration of the other solution.2022-10-53.3 Ways of Expressing Concentration of Standard Solution2022-10-52022-10-5Example A H2SO4 liquid,density is 1.84 g/mL,content of H2SO4 is 95.0%.Calculate the molarity of th
8、e H2SO4.Solution:n of H2SO4 per liter:n=m/M=1.84 1000 0.950/98.08 =17.9 mol c=n/V=17.9 mol/L2022-10-53.3.2 Titer1.Usually expressed as Ta/b such as TFe/KMnO4,the unit is g/mL.2.TFe/KMnO4=0.005682 g/mL implies that 1 mL of the standard KMnO4 solution is equivalent to 0.005682 g of iron.That is,1 mL o
9、f this solution can oxidize 0.005682 g of Fe2+to Fe3+.3.It is convenient to obtain the mass of the analyte from titer according to the following relation:m=TV,where m is the mass of the analyte,and V is the volume of the standard solution required in titration.2022-10-54.c is the molar concentration
10、 of the titrant,mol/L;a is the coefficient of analyte,b is the coefficient of the titrant,M is the molar mass of the analyte,g/mol.310 MTabc310 cMbaTba2022-10-53.4 Calculations in Titrimetric Analysis2022-10-5Relationships in titrimetry2022-10-5Example 2022-10-5Solution:2022-10-52.Diluting a solutio
11、n(1)In diluting a solution,the amount of the solute keeps constant,the volume and concentration changes.(2)So:c1V1 =c2V22022-10-5 Example2022-10-5Example2022-10-53.4.2 Calculation of the Percentage of the Analyte2022-10-5Example 2022-10-5ProblemsnA 0.7546g sample of KHP required 34.79mL of NaOH solution Calculate the concentration of the solution.Ans.0.1.62 molL-12022-10-5Nextchapter2022-10-5
