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1、Analytical chemistry2024/9/201Introduction to Analytical Chemistry22024/9/2032024/9/20 Analytical chemistry involves separating, identifying, and determining the relative amounts of the components making up a sample of matter. 分析化学分析化学包括包括样品分离、定性以及确定品分离、定性以及确定组成成分的成成分的相相对含量含量三方面内容三方面内容。 Qualitative
2、analysis reveals the chemical identity of the analytes. 定性分析定性分析是确定是确定被分析物被分析物(待待测物物)的化学的化学组成。成。42024/9/20 Quantitative analysis tells us the relative amounts of one or more of these analytes in numerical terms. 定量分析是确定一种或多种不同形式的被分析物的相定量分析是确定一种或多种不同形式的被分析物的相对含量。含量。 Qualitative information is require
3、d before a quantitative analysis can be undertaken. 在在进行定量分析之前需要先行定量分析之前需要先进行定性分析。行定性分析。 A separation step is usually a necessary part of both qualitative and qualitative analysis. 通常情况下，通常情况下，样品的品的预先分离是先分离是进行定性和定量分析行定性和定量分析之前必不可少的步之前必不可少的步骤。The role of analytical chemistry in the sciencenAnalytical
4、 chemistry, or the art of recognizing different substances and determined their constituents, takes a prominent position among the applications of science, since the questions which it enables us to answer arise whenever chemical processes are employed for scientific or technical purpose. n分析化学是一分析化
5、学是一门确定不同物确定不同物质组成及其含量的学科，成及其含量的学科，在科学在科学应用中用中处于主于主导地位。地位。这是由于分析化学可以是由于分析化学可以帮助我帮助我们解决所有利用化工能解决的科学和技解决所有利用化工能解决的科学和技术所所产生的生的问题。52024/9/20nIts supreme importance has caused it to be assiduously cultivated from a very early period in the history of chemistry, and its records comprise a large part of th
6、e quantitative work which is spread over the whole domain of science. n分析化学的重要性使其在化学分析化学的重要性使其在化学历史的最初期就得到史的最初期就得到了全面了全面发展，同展，同时分析化学分析化学记录包含了大部分的定包含了大部分的定量分析工作，并在整个科学量分析工作，并在整个科学领域得到广泛域得到广泛传播。播。62024/9/20nQuantitative analytical measurement also play a vital role in many research areas in chemistry,
7、 biochemistry, biology, geology, and the other sciences. n定量分析定量分析测量也在化学、生物化学、生物学、量也在化学、生物化学、生物学、地理学以及其他科学的地理学以及其他科学的许多研究多研究领域扮演者重域扮演者重要的角色。要的角色。72024/9/20nFor example, chemists unravel the mechanisms of chemical reactions through reaction-rate studies, the rate at which reactants are consumed or pr
8、oducts formed in a chemical reaction can be calculated from quantitative measurements made at equal time intervals. n比如，化学家通比如，化学家通过研究反研究反应速率来速率来阐明化学反明化学反应机理。机理。而化学反而化学反应中反中反应物的消耗速率或物的消耗速率或产物的生成速率可物的生成速率可以通以通过在相同在相同时间间隔下隔下进行定量行定量测计算得到。算得到。82024/9/20nQuantitative analysis for potassium, calcium, and
9、sodium ions in the body fluids of animals permit physiologists to study the role these ions play in nerve-signal conduction and muscle contraction and relaxation.n生理学家通生理学家通过对动物体液内物体液内钾离子、离子、钙离子和离子和钠离子的定量分析，来研究离子的定量分析，来研究这些离子在神些离子在神经信号信号传导和肌肉收和肌肉收缩和松弛中的作用。和松弛中的作用。92024/9/20nMaterials scientists rely
10、 heavily upon quantitative analysis of crystalline germanium and silicon in their studies of the behavior of semiconductor devices. n材料学家主要依材料学家主要依赖对晶体晶体锗和硅的定量分析来研究他和硅的定量分析来研究他们作作为半半导体元件的性能。体元件的性能。nImpurities in these devices are in the concentrations range 1*10-6 to 1*10-10 percent. n这些元件中的些元件中的杂质含
11、量在百分之含量在百分之1*10-6 到到 1*10-10 的的范范围内。内。 102024/9/20nArchaeologists identify the source of volcanic glasses by measuring the concentrations of minor elements in samples taken from various locations. n考古学家通考古学家通过测量从不同位置采集的量从不同位置采集的样品中的微量元品中的微量元素的素的浓度来确定火山玻璃岩的来源。度来确定火山玻璃岩的来源。nThis knowledge in turn make
12、s it possible to trace prehistoric trade routes for tools and weapons fashioned from obsidian. n以此以此类推，推，这种方法也有望用于史前流行的黑曜石工种方法也有望用于史前流行的黑曜石工具和武器的交易路具和武器的交易路线的追踪研究。的追踪研究。112024/9/20A classification of quantitative methods of analysisnWe compute the results of a typical quantitative analysis from two
13、productive amounts of the components making up a sample of matter. n典型的定量分析典型的定量分析结果是通果是通过计算算组成成样品的两种大品的两种大量成分的含量得到的。量成分的含量得到的。nQualitative analysis reveals the chemical measurements. n定性分析是指化学定性分析是指化学测量。量。122024/9/20nOne is the weight or volume of sample to be analyzed. n第一步是分析第一步是分析样品的重量或体品的重量或体积。
14、nThe second is the measurement of some quantity that is proportional to the amount of analyte in that sample. n第二步是第二步是测量与量与样品中被分析物相当的物品中被分析物相当的物质的量。的量。nThis seconds step normally completes the analysis. n第二步通常是完成分析的步第二步通常是完成分析的步骤。132024/9/20nChemists classify analytical methods according to the nat
15、ure of this final measurement. n化学家根据最后一步化学家根据最后一步测量的性量的性质对分析方法分析方法进行行分分类。nIn a gravimetric method, the mass of the analyte or of some compounds chemically related to it is determined.n 重量分析法是用来确定被分析物或其他一些化学重量分析法是用来确定被分析物或其他一些化学相关的物相关的物质的的质量。量。142024/9/20nIn a volumetric method, the volume of a solu
16、tion containing sufficient reagent to react completely with the analyzer is measured. n容量法是指用含有容量法是指用含有过量量试剂的溶液与被分析物完全反的溶液与被分析物完全反应，并，并测量反量反应的溶液的体的溶液的体积的方法。的方法。nElectro-analytical methods involve the measurement of such electrical properties as potential, current, resistance, and quantity of electri
17、city.n电化学分析法是化学分析法是测量量电化学性化学性质的方法，如的方法，如测量量电压、电流、流、电阻及阻及电量等。量等。152024/9/20nSpectroscopic methods are based upon measurements of the interaction between electromagnetic radiation and analyte atoms or molecules or upon the production of such radiation by analytes. n光光谱分析法是基于分析法是基于测量被分析物原子或分子与量被分析物原子或分
18、子与电磁磁辐射之射之间的相互作用，或的相互作用，或测量被分析物量被分析物产生的生的辐射的方射的方法。法。nFinally, a group of miscellaneous methods should be mentioned. n最后，最后，还应介介绍一一组不同种不同种类的分析方法。的分析方法。162024/9/20nThese include the measurement of such properties as mass-to-charge ratio (mass spectrometry), rate of radioactive decay, heat of reaction,
19、 rate of reaction, thermal conductivity, optical activity, and refractive index.n这些分析方法些分析方法测量被分析物的一些其他性量被分析物的一些其他性质，包括，包括荷荷质比（比（质谱），放射性衰），放射性衰变速率，反速率，反应热、反、反应速率、速率、导热性、光学活性（旋光度）以及折射率。性、光学活性（旋光度）以及折射率。172024/9/20Step in a typical quantitative analysisnSelecting a methodnSelecting which method to use
20、 to solve an analytical problem is a vital first step in any quantitative analysis. n在任何定量分析中在任何定量分析中选择分析方法是解决分析方法是解决问题至关重至关重要的第一步。要的第一步。nThe choice is sometimes difficult, an important consideration in selection is the accuracy required. n有有时很很难选择到合适的分析方法，其中一个至关重到合适的分析方法，其中一个至关重要的考要的考虑因素就是分析因素就是分析对
21、精确度的要求。精确度的要求。182024/9/20nUnfortunately, high reliability nearly always required a large investment of time. n但是，要但是，要获得高可信度一般需要花得高可信度一般需要花费大量的大量的时间进行分析。行分析。nThe chosen method is most often a compromise between accuracy and economics.n分析方法的分析方法的选择往往是往往是综合考合考虑了精确度和了精确度和经济性性两方面因素。两方面因素。 192024/9/20nSa
22、mplingnTo produce meaningful information, an analysis must be performed on a sample whose composition faithfully represents that of the bulk of material from which the sample was taken. n为了了获得有价得有价值的信息，分析所使用的的信息，分析所使用的样品必品必须能能够如如实地代表大部分被分析物的地代表大部分被分析物的组成。成。nWhere the bulk is large and inhomogeneous,
23、 great effort is required to get a representative sample.n当待当待测物物质是体是体积庞大并且大并且组成不均匀的成不均匀的样品品时，想要想要获得具有代表性的得具有代表性的样品并不容易。品并不容易。202024/9/20nConsider, for example, a railroad car containing 25 tons of silver ore. n例如，例如，试想有一想有一辆装有装有15吨吨银矿石的有石的有轨电车。nBuyer and seller must agree on the value of the shipme
24、nt based primarily its silver content. n买家和家和卖家家对这批批货物的价物的价值达成共达成共识，主要是依，主要是依据据货物中物中银的含量。的含量。nThe ore is inherently heterogeneous, consisting of productive amounts of the components making up a sample of matter.n矿石是内部均匀的，由大量的石是内部均匀的，由大量的组分构成的分构成的样品。品。 212024/9/20nPreparing a laboratory samplenAfter
25、sampling, solid materials frequently are ground to decrease particle size, mixed to ensure homogently, and stored for various lengths of time before the analysis begins. n取取样后，固体材料通常需要研磨成更小的后，固体材料通常需要研磨成更小的颗粒，并粒，并混合均匀，在分析之前需要混合均匀，在分析之前需要进过不同不同时间的的贮藏。藏。nDuring each of these steps, absorption or desor
26、ption of water may occur, depending upon the humidity of the environment.n在在这些步些步骤中，可能会中，可能会发生生样品的吸水和脱水，品的吸水和脱水，这主要取决于主要取决于环境的湿度。境的湿度。 222024/9/20nBecause any loss or gain of water changes the chemical composition of a solid, it is a good idea to carefully dry samples at the start of an analysis. n由
27、于任何水分的缺失或由于任何水分的缺失或获得都会引起固体得都会引起固体样品化学品化学组成的成的变化，因此，在化，因此，在对样品分析之前最好先品分析之前最好先进行行严格的干燥格的干燥处理。理。nAlternatively, the moisture content of the sample can be determined at time of the analysis in a separate analytical procedure.n另一种方法，另一种方法，样品中的水分含量可以在品中的水分含量可以在进行分析的行分析的同同时，通，通过单独的分析步独的分析步骤进行行测定。定。232024/
28、9/20nDefining replicate samplesnMost chemical analysis are performed on replicate samples whose weight or volumes have been determined by careful measurement with an analytical balance or with a precise volumetric device. n大部分的化学分析都是在随机抽大部分的化学分析都是在随机抽样样品上品上进行的，行的，这些些样品的重量和体品的重量和体积已已经通通过分析天平或精密体分析天平或
29、精密体积测量量设备测量量给出。出。nObtaining replicate data on samples improves the quality of the results and provides a measure of their reliability.n样品随机抽品随机抽样数据的数据的获得提高了分析得提高了分析结果的果的质量，并量，并可以可以测验其分析的可信度。其分析的可信度。 242024/9/20nPrepare solution of the samplenMost analysis are performed on solution of the sample. n大多
30、数的分析都是大多数的分析都是针对溶液溶液样品品进行的。行的。nIdeally, the solvent should dissolve the entire sample rapidly. n最理想的情况是最理想的情况是样品可以在溶品可以在溶剂中快速完全溶解。中快速完全溶解。nThe conditions of dissolution should be sufficient mild so that loss of the analyte can not occur.n应尽量避免待尽量避免待测物物质的分解，以减少由此造成的的分解，以减少由此造成的损失。失。252024/9/20nUnfort
31、unately, many materials that must be analyzed are insoluble in common solvents. n但是，但是，许多需要分析的待多需要分析的待测物物质在常在常规溶溶剂中很中很难溶解。溶解。nExamples include silicate minerals, high-molecule-weight polymers, and specimens of animal tissue. n这些物些物质包括硅包括硅矿石，高聚物以及石，高聚物以及动物物组织标本。本。nConversion of the analyte in such ma
32、terials to be a soluble form can be a difficult and time-consuming task. n将上述物将上述物质转变成可溶物形式成可溶物形式进行分析，是一行分析，是一项极极其困其困难又耗又耗时的工作。的工作。262024/9/20nCalibration an measurementnQualitative analysis reveals the chemical many lumps that vary in size as well as in silver content. n定性分析是分析定性分析是分析许多不同尺寸及多不同尺寸及银
33、含量的化学含量的化学块状状物。物。nThe analysis to have significance, this small sample must have a composition that is representative of the 25 tons ore in the shipment. n这种小的种小的样品必品必须能能够代表代表这批批25吨吨银矿石石货物的物的组成，成，这样定性分析才有意定性分析才有意义。272024/9/20nThe task is to isolate 1g of material that accurately reflects the average
34、 composition of the nearly 23000000g bulk sample. n取取样工作就是从待分析物中取出工作就是从待分析物中取出1g样品，并使其可品，并使其可以充分代表将近以充分代表将近23000000g样品的平均品的平均组成。成。nObtaining such a representative sample is a difficult undertaking that requires a careful, systematic manipulation of the entire shipment. n要想要想获得得这样具有代表性的具有代表性的样品相当不容易，
35、它需品相当不容易，它需要要对整个整个样品品进行仔行仔细的，系的，系统的的处理。理。282024/9/20Acids and basesnKey theory: Bronsted-Lowry theory of acids and bases: Acid-base reactions are ones in which protons are given and taken. Acids are proton donors, bases are proton acceptors.292024/9/20HF + H2O H3O+ + F H2O + NH3 NH4+ + OHAcid base C
36、onjugate Conjugate acid baseto be able to give protons, and acid must have a hydrogen atom which can be lost.to be a base, a substance must have a lone pair which can become a sigma pair as it accepts a proton.Conjugate pairs Every acid has what is called a conjugate base. This is the particle left
37、when the acid has given away its proton. In the same way, every base has a conjugate acid, which is the particle made when proton has arrived. So the conjugate base of HCl is Cl- - and the conjugate acid of ammonia is NH4+. Familiar conjugate pairs:302024/9/20- -AcHAc - - -2442HPOPOH- - -3424POHPO+
38、+34NHNHAmpholytesnThe water in the first reaction above is acting as a base, one of its lone pairs accepts a protons.nIn the second reaction the water is being an acid, giving one of its protons to ammonia. nSubstances like water, with hydrogens that can be lost and lone pairs that can be protoned,
39、are called ampholytes. They can be either acids or bases depending on what they react with. 312024/9/20HF + H2O H3O+ + F H2O + NH3 NH4+ + OHExercisenWhich are the conjugate pairs in the below? 322024/9/20 NH3、OH、Na+、NH2、NH4+、Cl、H+ 。nIs there any ampholyte? NH3NH2&NH4+NH3&NH3 IndicatorsnIndicators ar
40、e substances which change colour as the pH changes. An indicator is a weak acid whose conjugate base is a different colour. HInH3O+ + In- - colour A colour BnIn acid there will be a lot of H3O+ and so the equilibrium will lie to the left. The colour seen will be colour A. nIn alkaline conditions, al
41、l the H3O+ ions will be uesd up and the equilibrium will move to the right. The colour seen will be colour B. 332024/9/20 IndicatorsnWhen there are equal amounts of the two colours, HIn will equal In- - and the colour will be a mixture of A and B. This happens when pH=pKHIn as shown below. 1 HIn=In-
42、 -, so pH=pKHInnThe sudden change in colour seen in a titration is called the end-point. Some people are colour blind, but most people can detect a change in colour when the ratio of A to B is 1:10 or 10:1. This means most indicators have a useful pH change range of about 2 pH units. 342024/9/20=H+K
43、HInHInIn-Equivalence pointnThe equivalence point of the titration, when amounts of acid and base exactly balance, and the end point will be very close to each other if the correct indicator has been chosen. 352024/9/20Indicator structurenIndicator structure are quite complicated molecules whose elec
44、tronic structure changes as they are protonated or deprotonated. This change in electronic structure results in a change in electronic energy levels and so a change in colour. 362024/9/20H+ OH-red 3.1orange 4.0yellow 4.4pKa=3.4372024/9/20IndicatorPKInUseful pH rangeColour changeMethyl orange3.73.1-4
45、.4red to yellowBromophenol blue4.03.0-4.6yellow to blueMethyl red5.14.2-6.3red to yellow Bromothymol blue7.06.0-7.6yellow to bluePhenolphthalein9.38.0-9.6colourless to red382024/9/203.1 4.44.04.2 6.35.08.0 9.69.0Methyl orange MOMethyl red MRPhenolphthalein PPBuffer solutionsnBuffer solutions resist
46、changes in pH on addition of acid or alkali.nBuffer solutions tend to resist changes in pH when small amounts of acid or base are added and their pH is not affected by dilution.392024/9/20Buffer solutionsnAcid buffers are made of a solution of a weak acid and its conjugate base, e.g. a solution of e
47、thanoic acid and sodium ethanoate.nBasic buffers are made of a solution of a weak base and its conjugate acid, e.g. a solution of ammonia and ammonium chloride.402024/9/20How buffers work?nWe have seen that a buffer contains particles which can react with either any acid or any base which is added.4
48、12024/9/20CH3COOH + H2O CH3COO- - + H3O+nLots of spare acid molecules because ethanoic acid is a weak acid.nLots of spare conjugate base because sodium ethanoate has been added to the acid solution.Addition of a basenAny base that is added reacts with the hydroxonium ions, H3O+, and uses them up. Th
49、is means that there is no back reaction in the equilibrium, but the forward reaction goes on with more ethanoic acid molecules protonating water and replacing most of the hydroxonium ions that were removed by the base. So the pH hardly changes at all.422024/9/20CH3COOH + H2O CH3COO- - + H3O+Addition
50、 of a acidnAdding acid, that is more hydroxonium ions, H3O+, increases the rate of the back reaction as ethanoate ions collide more often with acid ions until most of the extra ones are removed. Once again the pH hardly changes.432024/9/20CH3COOH + H2O CH3COO- - + H3O+ExercisenChemical analyses can
51、be made by determining how much of a solution of known concentration is needed to react fully with an unknown test sample. The method is generally referred to as volumetric analysis and consists of titrating the unknown solution with the one of known concentration (a standard solution). By titration
52、, you can determine exactly how much of a regent is required to bring about complete reaction of the test solution. 442024/9/20nUsually, completion of the reaction is indicated by a sudden, visible change in the reaction system that coincides with the stoichimetric relationship between moles or equivalents of the regent solution and the reactant in the test solution. A drop or two of an appropriate indicator solution produces a colour change at the point where the reaction is complete-referred to as the endpoint. 452024/9/20Thank you!462024/9/20
