化学专业英语第六课仪器分析英文课件.ppt

1、Volumetric ANALYSIS,Introduction,Analytical Chemistry: determining the chemical composition of samples of matter. Qualitative analysis: identify of functional groups, or atomic, molecular structure of analyte ( what?) Quantitative analysis: amount of analyte ( how much?),3,定性分析 Qualitative analysis

2、物质的组成 定量分析 Quantitative analysis 成分的含量 结构分析 Structure analysis 物质的结构 DNA测序（DNA Sequencing) 形态分析 Species analysis 物质的形态 能态分析 Energy-state analysis 物质的能态,分析方法的分类,Classical methods (Chemical analysis),Qualitative analysis: Analytes,Products,recognized,yield,treated with reagents,Colors Boiling (melting

3、) points Solubilities Odors Optical activities Refractive indexes,Quantitative analysis: gravimetric; titrimetric,Instrumental methods (Instrumental analysis),Early in 20th century,Measurements of physical (chemical) properties of analytes: -conductivity; electrode potential; light absorption (emiss

4、ion); mass-to-charge ratio; fluorescence,Highly efficient chromatographic and electrophoretic techniques,replaced,Distillation, extraction, precipitation,a. Development of instruments and computer,b. Development of separation methods,c. Classification of instrumental analysis,Optical Analysis (spect

5、rometry); Electrochemical Analysis; Chromatography,General principles of volumetric analysis,Chemical analyses can be made by determining how much of a solution of known concentration is needed to react fully with an unknown test sample.,通过测定需要多少已知浓度的溶液与未知样品彻底反应来做化学定量分析。,The method is generally refe

6、rred to as volumetric analysis and consists of titrating the unknown solution with one of known concentration (a standard solution).,General principles of volumetric analysis,这个方法一般称为容量分析，由已知浓度（标准溶液）的溶液滴定未知浓度的溶液。,By titration, you can determine exactly how much of a reagent is required to bring abou

7、t complete reaction of the test solution.,General principles of volumetric analysis,通过滴定法，你可以准确测定需要多少试剂可完成实验溶液的完全反应。,Usually, completion of the reaction is indicated by a sudden, visible change in the reaction system that coincides with the stoichiometric relationship between moles or equivalents of

8、 the reagent solution and the reactant in the test solution.,General principles of volumetric analysis,通常，反应体系里完全完成的反应有一个可见的，突然的变化来预示；而这与试剂溶液及反应溶液中的反应物之间的摩尔或当量之化学计量关系是吻合的。,A drop or two of an appropriate indicator solution produces a color change at the point where the reaction is complete - referre

9、d to as the end point.,General principles of volumetric analysis,一到两滴合适的指示剂溶液在反应完成的那一点产生颜色的变化-称为终点 。,The normality of an acid or base of unknown concentration may be determined by titration. The advantage of using normality rather than molarity is that equal volumes of solutions of equal moralities

10、have identical capacities for neutralization, because they contain the same number of equivalent weights.,General principles of volumetric analysis,酸或碱的未知当量浓度可由滴定法来确定。这里使用当量浓度而不是摩尔浓度的优点是相同摩尔数的相同体积的溶液有相同的中和能力，因为它们所含的当量重量相同。,In a titration, we compare equivalent weights of acid and base. The number of

11、 equivalents of acid is equal to the product of the volume of the acid solution and its normality:,General principles of volumetric analysis,滴定中我们比较酸,碱的当量。酸的当量数等于酸溶液产品的体积和其当量浓度: Va X Na =equivalents of acid,Selecting an analytical method,What accuracy is required?-Accuracy/Bias How much sample is av

12、ailable?-sensitivity What is the concentration range of the analyte?-Dynamic range What components of the ample will cause interference?-Selectivity What are the physical and chemical properties of the sample matrix? -analytical methods How many samples are to be analyzed?-economic standpoint,Defini

13、ng the problem:,Precision and accuracy,15,精密度(precision)：在相同条件下，多次测定结果相互接近的程度。 偏差(diviation)：表示精密度的大小，偏差越小，测定结果的精密度越高。,精密度与偏差,所有滴定步骤都必须谨慎操作,Procedure of volumetric analysis,Care must be exercised throughout the titration procedure.,Titration of Vinegar According to the equation One molecule of NaOH

14、neutralizes one molecule of acetic acid, or one gram-molecule weight of NaOH neutralizes one gram-molecular weight of acetic acid. (gram-molecular weight, amount of a molecular substance whose weight, in grams, is numerically equal to the molecular weightof that substance.),Procedure of volumetric a

15、nalysis,Calculate the amount of acetic acid present in the vinegar. Report this amount as the percentage of acetic acid,Procedure of volumetric analysis,计算乙酸在食醋中的含量。 用乙酸的百分比报告这一含量,If pH meter is available, repeat the above process using a pH meter for constantly determining the pH. When the endpoint

16、 is reached, continue adding the base to expand the curve further. Make a graph for this titration.,Procedure of volumetric analysis,如果有pH计，那么重复上述过程，用酸度计持续不断测定pH值。当到达终点时，继续加碱使曲线进一步延伸。给这个滴定过程做图。,Calculate the percentage of acetic acid in vinegar.,Questions to consider,计算醋里乙酸的百分比。,What is the pH range for phenolphthalein?,Questions to consider,酚酞pH范围是什么（多少）？,Why should the solution in the flask constantly be stirred?,Questions to consider,为什么烧瓶中的溶液要不断的搅拌？,Consider a hypothetical experiment in which you weighted out 2.0g of oxalic acid and titrated it with 43ml of 1.5N NaO