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1、第十章电分析化学导论（Chapter x introduction to electrochemical analysis）The document comes from the network, it is my own collection organized, if have omitted, the error, still asks everyone to correct!Chapter x introduction to electrochemical analysisOne. Teaching content1. Basic concepts, classification an
2、d characteristics of electroanalytical chemistry2. Electrochemical battery, schematic and electromotive force3. Electrode and its classification and electrode potentialIi. Key points and difficulties1. The correct representation and related operation of the battery electromotive force2. The correct
3、expression of electrode potential and related operationIii. Teaching requirements1. Understand the classification clues and overall contents of electroanalytical chemistry2. Correctly master the battery electromotive force, electrode potential expression method and various related elements3. Master
4、the various classification methods of electrodes4. Schedule 3 hours in schoolElectroanalysis chemistry is an important branch of instrument analysis, is based on the electrochemical properties of solution of analysis method, or the use of material in the electrochemical properties of the solution an
5、d analyze the change rule of methodElectrochemical properties refer to the relationship between the electrical properties of the solution (such as conductance, electric quantity, current, etc.) and chemical properties (such as the composition, concentration, morphology and certain chemical changes o
6、f the solution)The classification and characteristics of electrochemical analysis1. Classification of electrochemical analysisThe relationship between the properties of electrochemical properties is divided into three categories: electroconductive analysis, potential analysis, electrolysis and coulo
7、mb analysis, polarography and volvo-analysis, etcAnd its usually divided into three types:1. The analysis method based on the direct relation between certain electrochemical parameters under certain experimental conditionsSuch as conductance method, potential method, coulomb method, polarography and
8、 voltammetry2. In the process of titration, the mutation of certain electrochemical parameters is used as the method to indicate the end point in titration analysis (note: no indicator), such as potentiometric titration, conductance titration, current titration, etc3. The electronic as precipitant,
9、a substance under test in the test solution through the electrode reaction is converted into solid deposition on the electrode, the electrode method, an analysis of the amount of deposits such as electrolytic method (also known as electric weight method)According to the recommendations of the IUPAC
10、(international federation of pure and applied chemistry) 1975See, divide into three categories:1. Neither the double layer nor the method of electrode reaction, such as conductance analysis and high frequency titration, are not involvedIt involves only two layers of electricity, but not the method o
11、f electrode reactions, such as surface tensiometry and non-faraday impedance measurements3. Methods of electrode reaction, such as potential analysis, electrolytic analysis, coulomb analysis, polarography and voltammetryThis course is about the third method2. Characteristics of electrochemical analy
12、sis1. The instruments used are simpler, smaller and cheaperBecause the parameters of measurement are electrical signals, convenient and easy to be automated and continuous;2. Determination of fast and simple;3. The sensitivity of some new methods is high, which can be used for trace or ultra trace a
13、nalysis, and the selectivity is better.Not only can the composition content be analyzed, it can also be used for price, morphological analysis, but also as a tool for scientific research in other fieldsComposition of chemical batteriesSimple chemical batteries consist of two groups of metal-electrol
14、yte solutionsThis metal - solution system called electrode (sometimes called a half cell), two electrode metal parts through wires connected to external circuit, two electrode solution part must communicate with each other, to form a loopIf two metals of the electrode are immersed in the same electr
15、olyte solution, the cell formed is called a non-liquid junction electrodeIf the two metals are immersed in different electrolytesThe two solutions are separated by sintered glassOr use a salt bridge to connectThe batteries formed are called liquid junction cellsWhen the battery is working, the curre
16、nt forms the loop through the inside and outside of the batteryThe external circuit is a metal conductor, and the electrons that are moving are negativeThe inside of the battery is an electrolyte solution, which moves the positive and negative ions respectivelyThe current is going to go through the
17、whole loop,The oxidation-reduction electrode reaction, which must occur on the metal/solution interface of the two electrodes, is that the ions take electrons from the electrodes or hand the electrons to the electrodesA diagram of the batteryThe battery can be expressed in a certain graphical formDa
18、niel (Danill) battery can be expressed as:The battery reaction shown in the graphic expression is:The battery schematic rules are:1. The left side of the equation is the electrode of the oxidation reaction, known as the Anode. Type on the right is the reduction reaction of electrode, known as the Ca
19、thode (Cathode)And two electrodes in the actual for the positive electrode potential is high, low electrode potential of the cathode (note: the galvanic anode to cathode, cathode to the anode; electrolytic cell anode for the anode, cathode to anode)2. The two phase interface or between two mutually
20、soluble solution in order to |, said the salt bridge between the two electrodes, have been eliminate liquid junction potential use | | or said3. The electrolyte solution that makes up the electrode must be clear and labeled, indicating activity (concentration); If the electrode reaction is involved
21、in gas, the degree of fugacity (pressure) and temperature should be indicated (the unlabeled is 1 atmosphere, 25oC).4. For electrode gas or homogeneous electrode reaction, do not in themselves as support the body of the electrode reaction substances, must be inert electrodes, also need to watch out,
22、 the most commonly used Pt electrode, such as the standard hydrogen electrode (SHE) : Pt, 2 (1 ATM) | H + H (1 mol/L)The electromotive force of the batteryThe cells electromotive force E is the electrical potential difference between the two electrodes of the batteryBy the batteryThe left-hand side
23、represents the anode and the cathode on the rightSo the battery electromotive forceThe relationship between delta G and cell electromotive force E is:(n is the electron transfer number of the reaction, F is Faraday constant)The formation and expression of electrode potentialThe formation of electrod
24、e potential is illustrated by the electric power of metal and its salt solutionWhen the electrode potential of an electrode is determined, the electrode and SHE will be composed of a primary battery:SHE | | for the electrodeThe electromotive force of the battery is the electrode potential of the ele
25、ctrode(note: in the potentiometer, SHE is generally used as the standard, and in the practical use of electrochemical analysis, the SCE of saturated calomel electrode is often standard.)The electrode reaction is called a semi-cell reaction, and the semi-reaction is usually written as a reduction rea
26、ction.Electrode potential is expressed as:Type: aoAR is the activity of the oxidation state and the original state material in the half reaction, the electron transfer number of the unit half reaction is n, and the phi o is aoAR is the electrode potential of 1 mol/l-1 (or 1), which is called the sta
27、ndard electrode potential of the electrodeR is the gas constant (8.314 J/mol K, F is the farad constant 96487C/mol), and K is the kelvin temperatureThe influence of ion strength is only considered as an example:A = gamma c gamma is the activity coefficient (depending on the ion intensity) c is the m
28、olar concentrationWhen CO = CR = 1 mole of l-1,So Nernst equation is:If other conditions exist, the logarithm of phi O type should also include other related constants, and C is the concentration of C in the Nernst equationClassification of electrodesThere are two types: electrodes based on electron
29、 exchange reaction and ion exchangeOr the spreading electrodeThere are five types of electrodes:1. The first type of electrodeThe electrode (reactive metal electrode) of metal and its ion solution system (reactive metal electrode) | | : silver, mercury, copper, lead, zinc, cadmium and other electrod
30、esSo phi is only associated with the activity of Mn plus.2. Type ii electrodesMetal and its insoluble salts (or complex ions) and anions (or coordination ions) of refractory salt (or coordination ion) are used to form the electrode of the system of the system of the two components: silver - chlorina
31、ted silver electrode (Ag/AgCl, Cl -).So:Similar and commonly used electrodes have the calomel electrode (Hg/Hg2Cl2)Cl -); Metal andIt is composed of complex ionsElectrodes such as silver - silver cyanide ion electrode (Ag/Ag (CN) 2 -CN -)The electrode potential of the second electrode depends on the
32、 activity of the anion.So you can use it as an indication electrode for the anion. Silver - chloride silver electrode and calomel electrode (especially saturated calomel electrode) are often used as secondary standard electrode in electrochemistryThe third type of electrodeMetals have the same anion
33、ic insoluble salts (or dissociation complexes) as well as the firstThe electrode of a system composed of two types of insoluble salts (or complexes)These two kinds of difficultIn the salt solution (or complex), the negative is the same, while the cationic is the gold that makes up the electrodeOf th
34、e ions, the other is the ionSuch as:Zero class electrodeThe inert metal is the electrode of the soluble oxidation state and the original solution (or gas)The inert electrode itself does not have an electrode reaction, only the dielectric effect of electron transfer, the most commonly used is Pt elec
35、trode| | : Pt | Fe3 + (a1), Fe2 + (a2), Pt | Ce4 + (a1), Ce3 + (a2), hydrogen electrode and so on5. Membrane electrodeWith sensitive membrane and produce membrane potential of electrode (electrode) based on ion exchange or diffusion sensitive film is about a kind of ion has sensitive response to the
36、 membrane, the membrane potential and the response of its ion activity obey the Nernst equation, the relationship between the whole membrane electrode electrode potential is also obey the Nernst equationIn addition, there are useful electrodes:6. Microelectrodes or ultra-micro electrodesThe electrod
37、e, made of Pt wire or glass carbon fiber, has many excellent properties for some special Microsystems, such as the study of life sciences7. Chemical modification electrode (CME)Pt or glass carbon electrode surfaces with covalent bonding or strong adsorption or high polymer coating methods, modify th
38、e group with a certain function on the surface of the electrode to make electrodes with special propertiesReference - work - auxiliary electrode1. Indicating electrodeTo indicate the activity of the electrode surface to be measured on the ion, in the process of measuring the body of the solutionThe
39、electrodes of a system where the concentration does not changeIf the electrode of potential measurement, the current in the measurement loop is almost zero, the electrode reaction is basically nonexistent, and the body concentration is almost constant2. Working electrodesThe electrode used to genera
40、te the required electrochemical reaction or response excitation signal in the process of measuring the change of the concentration of the solution bodySuch as cathode in electrolytic analysis3. Reference electrodeIt is used to provide the standard potential, which does not vary with the component an
41、d concentration of the measurement systemThe electrode must have good reversibility, reproducibility and stabilityThe common reference electrodes are SHE, Ag/AgCl, Hg/Hg2Cl2 electrode, especially for SCEThe phi of the Hg/Hg2Cl2 electrode depends on the aCl -At 25 ocCKCl (mol L 1)0.11.0saturatedPhi (
42、V)+ 0.3365+ 0.2828+ 0.24384. Auxiliary electrodes - or electrodesIn electrochemical analysis or research work, often using three electrode system, in addition to the working electrode and reference electrode, still need to the third electrode, the electrode of electrochemical reaction is not measure
43、d or institute needs, electrode only as the place of electron transfer to and working electrode current loop, this electrode is called auxiliary electrodes or the electrodesDepolarization and polarizing electrodes1. Depolarize the electrodeIn electrochemical measurements, the electrode potential doe
44、s not change with the applied voltage, orThe electrode potential changes from a very small current to a very large electrodeThe ion selection electrode in saturated calomel electrode and potential analysis is extremely polarizing electrode2. Polarizing electrodeIn electrochemical measurements, the e
45、lectrode potential changes with the addition of the applied voltage, or the electrode potential changes a lot of the current changes in the electrodeWhen polarized electrode is polarized, the electrode potential will deviate from the potential of the equilibrium system and the deviation value is cal
46、led overpotentialThe electrode in the working electrode and polarographic analysis in the analysis of electrolysis and in the analysis of the polarographic analysis are polarizable electrodesCauses of polarization (two main types)Concentration polarizationReversible and rapid surface of the electrod
47、e reaction electrode reactions to reduce the concentration of the ions in the liquid layer (or higher) - - the ontology and solution on the surface of the electrode reaction ion concentration, form a certain concentration gradient - generate fluid concentration polarization - electrode surface layer of ion concentration determines the potential of the electrode, the potential balance of deviation from the electrode potential, deviation value is called concentration overpotential2. Electrochemical polarizationElectrode reaction speed slower - whe