The main types of chemical reactions in analytical chemistry. Questions for the analytical chemistry exam
Introduction
Subject of analytical chemistry, its structure; place in the system of sciences, connection with practice. Main analytical problems: lower detection limit; improving accuracy and selectivity; ensuring expressness; non-destructive analysis; local analysis; remote analysis. Types of analysis: isotopic, elemental, structural-group (functional), molecular, real, phase. Chemical, physical and biological methods of analysis. Macro-, micro- and ultramicroanalysis.
The main stages in the development of analytical chemistry. Current state and development trends of analytical chemistry: instrumentalization, automation, mathematization, miniaturization, increase in the share of physical methods, transition to multicomponent analysis, creation of sensors and test methods. Scientific chemical-analytical literature.
Metrological foundations of chemical analysis
The main stages of chemical analysis. Choice of analysis method and drawing up analysis schemes. Basic metrological concepts and representations: measurement, methods and means of measurement, errors. Analytical signal and interference. Methods for determining the content according to analytical measurements.
The main characteristics of the method and methodology of analysis: correctness and reproducibility, sensitivity coefficient, detection limit, lower and upper limits of the determined contents.
Classification of analysis errors. Systematic and random errors. Errors of individual stages of chemical analysis. Methods for evaluating the correctness: the use of standard samples, the method of additions, the method of varying weights, comparison with other methods. Statistical processing of measurement results. The law of normal distribution of random errors, t- and F-distribution. Mean, variance, standard deviation. Testing the hypothesis of normality, hypothesis of homogeneity of measurement results. Comparison of variance and means of two methods of analysis. Regression analysis.
Requirements for the metrological characteristics of methods and techniques depending on the object and purpose of the analysis. Ways to improve the reproducibility and correctness of the analysis
Types of chemical reactions and processes in analytical chemistry
The main types of chemical reactions in analytical chemistry: acid-base, complex formation, oxidation-reduction. Equilibrium constants of reactions and processes. State of substances in ideal and real systems. Solvation, ionization, dissociation. Behavior of electrolytes and non-electrolytes in solutions. Debye-Hückel theory. Activity coefficients. concentration constants. Total and equilibrium concentrations. Conditional constants.
The rate of reactions in chemical analysis. Fast and slow reactions. Factors affecting speed. Catalysts, inhibitors. autocatalytic reactions. Induced and coupled reactions. The concept of inductor, actor, acceptor.
Acid-base reactions.
Modern concepts of acids and bases (Lewis theory). Bronsted-Lowry theory. Acidity and basicity constants. Acid and basic properties of solvents. Autoprotolysis constant. Influence of the nature of the solvent on the strength of the acid and base; leveling and differentiating effect of the solvent.
Buffer solutions and their properties. buffer capacity. Calculation of the pH of solutions of acids and bases, polybasic acids and bases, mixtures of acids and bases. The concept of the isoelectric point of amino acids and proteins.
Complex formation reactions
. Types of complex compounds used in analytical chemistry. Classification of complex compounds according to the nature of the interaction of the central ion (complexing agent) ─ ligand, according to the homogeneity of the ligand and the central ion: inner-sphere complexes and ion associates (outer-sphere complexes and ion pairs); homoligand and mixed ligand; polynuclear (heteropolynuclear and homopolynuclear). Properties of complex compounds of analytical significance: stability, solubility, color, volatility.
Stepwise complexation. Stepwise and general stability constants of complex compounds. Factors affecting complex formation: structure of the central atom and ligand, concentration of components, pH, ionic strength of the solution, temperature. Classification of complex compounds according to thermodynamic and kinetic stability.
Influence of complex formation on the solubility of compounds, acid-base balance, redox potential of systems, stabilization of various degrees of oxidation of elements. Methods for increasing the sensitivity and selectivity of analysis using complex compounds.
Organic reagents in chemical analysis. Influence of the general structure of organic reagents on their properties. Functional-analytical groups (FAGs). Influence of the nature, location of FAG, stereochemistry of reagent molecules on its interaction with inorganic ions. Using theories of analogies and "soft" and "hard" acids and bases to explain the action of organic reagents. The main types of compounds formed with the participation of organic reagents. Chelates, intercomplex compounds. Factors that determine the stability of chelates: the nature of the metal-ligand bond, the size of the cycle, the number of cycles.
The most important organic reagents used for the detection and determination of metal ions, for masking and unmasking, separation. Organic reagents most commonly used in biochemical methods of analysis.
Possibilities of using organic reagents in various methods of analysis.
Redox reactions
. Electrode potential. Nernst equation. Standard and formal potentials. Connection of the equilibrium constant with standard potentials. The direction of the oxidation and reduction reaction. Factors affecting the direction of redox reactions. The main inorganic and organic oxidizing and reducing agents used in the analysis. Methods of preliminary oxidation and recovery of the determined component.
Chromatographic methods of analysis
Definition of chromatography. The concept of mobile and stationary phases. Classification of methods according to the state of aggregation of the mobile and stationary phases, according to the separation mechanism, according to the execution technique. Methods for obtaining chromatograms (frontal, displacement, eluent). Basic parameters of the chromatogram. Basic equation of chromatography. Selectivity and efficiency of chromatographic separation. Theory of theoretical plates. Kinetic theory. Qualitative and quantitative chromatographic analysis.
Gas chromatography
. Gas-adsorption (gas-solid-phase) and gas-liquid chromatography
. Sorbents and carriers, requirements for them. separation mechanism. Columns. Detectors, their sensitivity and selectivity. Applications of gas chromatography.
Liquid chromatography
. Types of liquid chromatography: adsorption (normal-phase and reversed-phase variants), ion-exchange, size-exclusion. Benefits of High Performance Liquid Chromatography (HPLC). Features of stationary and mobile phases. separation mechanisms. Pumps, columns. Main types of detectors, their sensitivity and selectivity. Applications of liquid chromatography.
Planar chromatography
. General principles of division. Methods for obtaining planar chromatograms (ascending, descending, circular, two-dimensional). Reagents for the development of chromatograms. Paper chromatography. separation mechanisms. moving phases. Advantages and disadvantages. Thin layer chromatography. separation mechanisms. Sorbents and mobile phases. Areas of use.
Titrimetric methods of analysis
Methods of titrimetric analysis. Classification. Requirements for the reaction in titrimetric analysis. Types of titrimetric determinations: direct, reverse, indirect titration. Methods for expressing concentrations of solutions in titrimetry. Equivalent. Molar mass of the equivalent. Primary standards, requirements for them. Fixanals. secondary standards. Types of titration curves. Titration jump. Equivalence point and end point of the titration. Automatic titrators.
Acid-base titration
. Construction of titration curves. Influence of the value of acidity or basicity constants, concentration of acids or bases, temperature, ionic strength on the magnitude of the jump on the titration curve. Acid-base titration in non-aqueous media. Acid-base indicators. Titration errors in the determination of strong and weak acids and bases, mixtures of acids and bases.
Redox titration.
Construction of titration curves. Factors affecting the magnitude of the jump on the titration curve: the concentration of hydrogen ions, the formation of complexes and poorly soluble compounds, ionic strength, temperature. Methods for determining the end point of the titration; indicators. Titration errors.
Methods of redox titration. Permanganatometry. Iodometry and iodimetry. The iodine-iodide system as an oxidizing or reducing agent. Bichromatometry. Primary and secondary standard solutions, methods of fixing the end point of titration. Indicators.
complexometric titration.
The use of aminopolycarboxylic acids. Construction of titration curves. Metal-chromic indicators and requirements for them. The most important universal and specific metallochromic indicators. Methods of complexometric titration: direct, reverse, indirect. Selectivity of titration and ways to increase it. Titration errors.
Examples of practical application.
Electrochemical methods of analysis
General characteristics of electrochemical methods. Classification. electrochemical cells. Indicator electrode and reference electrode. Equilibrium and non-equilibrium electrochemical systems and their use in various electrochemical methods.
Potentiometry
Direct potentiometry . Potential measurement. Reversible and irreversible redox systems. indicator electrodes. Ionometry. Classification of ion-selective electrodes. Characteristics of ion-selective electrodes: electrode function, selectivity coefficient, response time.
Examples of practical application of ionometry.
Potentiometric titration . Change in electrode potential during titration. Methods for detecting the endpoint of a titration. The use of acid-base reactions, precipitation, complexation, redox.
Examples of practical application.
Spectroscopic methods of analysis
Spectrum of electromagnetic radiation (energy, ways of its expression; terms, symbols and units of radiation energy; radiation ranges, types of energy transitions). The main types of interaction of matter with radiation: emission (thermal, luminescence), absorption, scattering. Classification of spectroscopic methods by energy. Classification of spectroscopic methods based on the spectrum of electromagnetic radiation (atomic, molecular, absorption, emission spectroscopy).
Spectra of atoms. Ground and excited states of atoms, characteristics of states. Energy transitions. Selection rules. Laws of emission and absorption. Probabilities of electronic transitions and lifetimes of excited states. Characteristics of spectral lines: position in the spectrum, intensity, half-width.
Spectra of molecules; their features. Schemes of electronic levels of a molecule. The idea of the total energy of molecules as the sum of electronic, vibrational and rotational. Dependence of the types of the spectrum on the state of aggregation of matter.
Relationship between the analytical signal and the concentration of the analyte.
Equipment. Ways of monochromatization of radiant energy. Classification of spectral instruments. Instrumental interference.
Methods of atomic optical spectroscopy
Atomic emission
method
. Sources of atomization and excitation: electric discharges (arc, spark, reduced pressure), flames, inductively coupled plasma, lasers. Main characteristics of atomization sources: plasma temperature, flame composition, electron concentration. Physical and chemical processes in sources of atomization and excitation.
Qualitative and quantitative analysis. The Lomakin-Schaibe equation and the reasons for the deviation from the Boltzmann law. Spectral, chemical and physico-chemical interference, ways to eliminate them.
Methods of atomic emission spectroscopy. Flame emission photometry, inductively coupled plasma atomic emission spectroscopy, spark atomic emission spectroscopy and their comparison. Metrological characteristics and analytical capabilities.
Atomic fluorescence method.
The principle of the method; features and application.
Atomic absorption method
. Atomizers (flame and non-flame). Basic law of light absorption in atomic absorption spectroscopy. Radiation sources (hollow cathode lamps, continuous spectrum sources, lasers), their characteristics. Spectral and physico-chemical interference, ways to eliminate them. Possibilities, advantages and disadvantages of the method, its comparison with atomic emission methods (accuracy, selectivity, sensitivity, rapidity).
Examples of practical application of atomic emission and atomic absorption methods in biochemical methods of analysis.
Methods of molecular optical spectroscopy
Molecular absorption spectroscopy (spectrophotometry).
Relationship between the chemical structure of a compound and the absorption spectrum. Functional analysis on vibrational and electronic spectra.
The basic law of light absorption (Bouguer-Lambert-Beer). Deviations from the law, their causes (chemical, physico-chemical, instrumental). The concept of true and apparent molar absorption coefficient. Photometric reaction and photometric analytical reagents; requirements for them. Instruments in spectrophotometry. Methods for determining the concentration of substances. Analysis of multicomponent systems. Analytical possibilities and limitations of the method. The role of sample preparation in spectrophotometry. Examples of practical application of the method.
Molecular luminescent spectroscopy.
General classification of molecular luminescence. Yablonsky's scheme. Fluorescence and phosphorescence. Stokes-Lommel law. Levshin's mirror symmetry rule. Energy and quantum yield. Vavilov's law. Luminescence quenching. Luminescent qualitative and quantitative analysis. Advantages of luminescent spectroscopy in the identification and determination of organic compounds. Devices in luminescence. Metrological characteristics and analytical capabilities of the method.
Examples of practical application of the method in biochemical methods of analysis.
Sampling and sample preparation
representativeness of the sample; sample and object of analysis; sample and method of analysis. Methods for obtaining a representative sample of solid, liquid and gaseous substances. Sampling of homogeneous and heterogeneous composition. Devices and techniques used in sampling; primary processing and storage of samples. The main methods for converting a sample into the form required for a particular type of analysis are: dissolution in various media; sintering, fusion, decomposition under the action of high temperatures, pressure, high-frequency discharge; combination of various techniques; features of the decomposition of organic compounds. Features of sampling and preparation when working with biological samples. Methods for eliminating and accounting for contamination and loss of components during sample preparation.
- Fundamentals of analytical chemistry (under the editorship of Yu.A. Zolotov). In 2 books. General issues. Separation methods. Methods of chemical analysis. M.: Higher school. 2004. 361, 503 pp. Series "Classical university textbook".
- Fundamentals of analytical chemistry. Practical guide. Textbook for universities. Ed. Yu.A. Zolotova. M.: Higher school. 2001. 463 p.
- Fundamentals of analytical chemistry. Tasks and questions. Textbook for universities. Ed. Yu.A. Zolotova. M.: Higher school. 2004. 412 p.
Additional
- Zolotov Yu.A. Analytical chemistry: problems and achievements. M.: Nauka, 1992, 288 p.
- Vasiliev V.P. Analytical chemistry. In two books. Moscow: Bustard, Book. 1. 2004, Prince. 2. 2005.
- Dorohova E.N., Prokhorova G.V. Tasks and exercises in analytical chemistry. M.: Publishing House of Moscow. un-ta, 1984. 215 p.
- Otto M. Modern methods of analytical chemistry (in 2 volumes). / Per. with him. and ed. A.V. Garmash. T.1. M.: Technosfera, 2003. 412 p. T.2. M.: Technosfera, 2004. 281 p.
- Analytical chemistry. Problems and approaches. In 2 volumes. (Translated from English under the editorship of Yu.A. Zolotov) M .: Mir. 2004.
- Lurie Yu.Yu. Handbook of analytical chemistry. Moscow: Chemistry, 1989.
The program is drawn up
Assoc. Veselova I.A.
Editor Prof. Shekhovtsova T.N.
2.1. General questions of the theory of solutions
Solution as a medium for analytical reactions. Influence of physico-chemical characteristics of the solvent on the chemical-analytical properties of ions. Fundamentals of the theory of strong electrolytes. Activity, activity coefficient, ionic strength of solutions.
Main types of chemical reactions used in analytical chemistry
Acid-base balance. Equilibrium in aqueous solutions of acids, bases and ampholytes. Buffer solutions, their composition and properties. Calculation of the pH of protolytic systems based on the Brønsted–Lowry theory. Application of acid-base interaction reactions in analytical chemistry. Importance of buffer systems in chemical analysis.
Redox balance. Conjugated redox couple. Redox potential and factors influencing its value. Redox reactions, their equilibrium constant, direction and speed. Autocatalytic and induced reactions, their role in chemical analysis. Application of oxidation-reduction reactions in analytical chemistry.
Equilibrium of complexation. Structure and properties of complex compounds. Polydentate ligands, chelate complexes, chelate effect. Equilibria in solutions of complex compounds, stability constants of complex ions. Use of complex formation reactions in analytical chemistry.
Equilibrium in the precipitate–solution system. Heterogeneous chemical equilibrium in solutions of sparingly soluble electrolytes. The solubility product rule and its use in analytical chemistry. Solubility constant (product of activities). Factors affecting the solubility of poorly soluble compounds: salt effect, the influence of ions of the same name and competing reactions. Use of heterogeneous systems for analytical purposes.
Organic analytical reagents
Features of organic analytical reagents: high sensitivity and selectivity of action. The use of organic analytical reagents in the analysis.
CHEMICAL SEPARATION AND DETECTION METHODS
3.1. General questions of qualitative analysis
Goals and objectives of qualitative analysis. Classification of qualitative analysis methods depending on the size of the sample. Experimental technique: high-quality test-tube, drop and microcrystalloscopic reactions.
analytical effect. Analytical chemical reactions and conditions for their implementation. General, group and characteristic (selective and specific) reactions.
Analytical classifications of cations and anions. Analytical groups of ions and the Periodic law of D. I. Mendeleev. Systematic and fractional qualitative analysis.
Use of precipitation, complex formation, acid-base and redox reactions in qualitative analysis. Organic analytical reagents, their advantages and applications in qualitative analysis.
Methods for the separation and detection of ions of greatest importance in chemical technology
I analytical group of cations. General characteristics. Characteristic reactions of Na + , K + , NH 4 + and Mg 2+ ions. Methods of decomposition and removal of ammonium salts. Systematic analysis of a mixture of group I cations.
II analytical group of cations. General characteristics, group reagent. Characteristic reactions of Ca 2+ and Ba 2+ ions. Optimal conditions for precipitation of group II cations. Systematic analysis of a mixture of group II cations and a mixture of group I–II cations.
III analytical group of cations. General characteristics, group reagent. Characteristic reactions of Al 3+ , Cr 3+ , Fe 3+ , Fe 2+ , Mn 2+ and Zn 2+ ions. Optimal conditions for precipitation of group III cations. Systematic analysis of a mixture of group III cations and a mixture of group I–III cations.
I analytical group of anions. General characteristics, group reagent. Characteristic reactions of ions CO 3 2– , SO 4 2– , PO 4 3– .
II analytical group of anions. General characteristics, group reagent. Characteristic reactions of ions Cl - , I - .
III analytical group of anions. General characteristics. Typical reactions of NO 2 - , NO 3 - ions. Analysis of a mixture of anions of groups I–III.
Analysis of an unknown substance
The main stages of qualitative chemical analysis are: preparation of a substance for analysis, taking an average sample, dissolving solids, preliminary tests, analysis of cations and anions.
Description of the presentation on individual slides:
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Analytical reactions in solutions Analytical reactions in solutions, reversible and irreversible Chemical equilibrium Law of mass action, chemical equilibrium constant Factors influencing the equilibrium shift of analytical reactions
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Types of chemical reactions in analytical chemistry acid-base reactions - reactions with H+ proton transfer redox reactions (ORR) - reactions with electron transfer ē complex formation reactions - reactions with electron pair transfer and formation of bonds according to the donor-acceptor mechanism Precipitation reactions - heterogeneous reactions in solution
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In quantitative analysis, reversible reactions are widely used, i.e. proceeding simultaneously in two opposite directions: aA + cB ↔ cC + dD The reaction proceeding towards the formation of reaction products is called direct aA + cB → sC + dD , all reactions occurring in nature are reversible, but in cases where the reverse reaction is very weak, the reactions are considered practically irreversible. These usually include those reactions during which one of the products formed leaves the reaction sphere, i.e. precipitate, are released in the form of a gas, a poorly dissociated substance (for example, water) is formed, the reaction is accompanied by the release of a large amount of heat.
4 slide
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The state of chemical equilibrium is typical only for reversible processes. In reversible reactions, the rate of the direct reaction initially has a maximum value, and then decreases due to a decrease in the concentration of the initial substances consumed to form the reaction products. The reverse reaction at the initial moment has a minimum rate, which increases with increasing concentrations of the reaction products. Thus, there comes a moment when the rates of the forward and reverse reactions become equal. This state of the system is called chemical equilibrium
5 slide
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In 1864 - 1867, the Norwegian scientists Guldberg and Waage established the law of mass action (under the effective masses they meant concentrations. Then the term concentration was not yet known, it was introduced later by van't Hoff): the rate of a chemical reaction is directly proportional to the product of the concentrations of reacting substances in powers, equal to the corresponding stoichiometric coefficients. For a reversible reaction of the type aA + vB = cC + dD, according to the law of action of masses, the rates of the forward and reverse reactions are respectively equal: vreq = kreq[A]a[B]v, vrev = krev[C]c[D]d. If vrev = vorev, then krev[A]a[B]v = korev[C]c[D]d, whence K = karev / krev = [C]c[D]d / [A]a[B]v . Thus, the equilibrium constant is the ratio of the product of the concentrations of the reaction products to the product of the concentrations of the starting substances. The equilibrium constant is a dimensionless quantity, since depends on the concentration and amount of substances.
6 slide
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The value of K, which characterizes the constancy of the ratios of equilibrium concentrations of reagents at a constant temperature, was called by van't Hoff the equilibrium constant. The equilibrium constant is one of the quantitative characteristics of the state of chemical equilibrium. Task: write an expression for the equilibrium constant of the following reactions: H2+I2 ↔ 2HI ; K= 2 / N2+3H2 ↔ 2NH3; K=2 / 3
7 slide
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The direction of the shift of chemical equilibrium with changes in concentration, temperature and pressure is determined by the principle of Le - Chatelier: if the system in equilibrium is affected (change in concentration, temperature, pressure), then the equilibrium in the system shifts in the direction of weakening this effect LE CHATELIER Henri Louis
8 slide
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For the reaction A + B ↔ C + D Concentration change If the concentration of the starting substances increases, then the equilibrium shifts towards the formation of reaction products, i.e. to the right A + B → C + D, if the concentration of the starting substances decreases, then the equilibrium shifts towards the starting substances, i.e. to the left A + B ← C + D if the concentration of reaction products increases, then the equilibrium shifts towards the formation of the starting substances, i.e. to the left A + B ← C + D, if the concentration of reaction products decreases, then the equilibrium shifts towards the formation of reaction products, i.e. right, A+B → C+D
9 slide
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For the reaction A + B ↔ C + D to the right A + B → C + D, if the temperature increases, then the equilibrium shifts towards the starting substances, i.e. to the left A + B ← C + D in an endothermic process (positive value of the reaction) - if the temperature increases, then the equilibrium shifts towards the formation of reaction products, i.e. to the right A + B → C + D, if the temperature decreases, then the equilibrium shifts towards the formation of the starting substances, i.e. left A+B ← C+D
Analytical reactions and analytical reagents are often (usually) subdivided into specific(specific, characteristic) , selective(electoral) and group.
Specific reagents and reactions make it possible to detect a given substance or a given ion in the presence of other substances or ions.
So, for example, if the solution contains molecular iodine I 2 , (more precisely, a more complex compound - triiodide ion I 3 -), then when a freshly prepared aqueous solution of starch is added, the initial solution turns blue. The process is reversible; when molecular iodine disappears in a solution (for example, when it is reduced to iodide ions I -), the blue color also disappears and the solution becomes colorless. This reaction is widely used in qualitative and quantitative chemical analysis. It was first described in 1815 by the German chemist F. Stromeyer.
The blue coloration of a starch solution in the presence of iodine (namely, triiodide ions, since pure molecular iodine I 2 does not stain starch even in the absence of iodide ions I) is explained by the formation of an adsorption complex between colloidal macromolecules of starch (fractions of unbranched amylose) and triiodide- ions.
A specific reagent for NO 2 nitrite ions is the Griess reagent - Iloshvay (Ilosvaya), which is a mixture of α-naphthylamine C 10 H 7 NH 2 and sulfanilic acid HO 3 SC 6 H 4 NH 2), with which the nitrite ion (usually in the presence of acetic acid) forms an azo dye HO 3 SC 6 H 4 N \u003d NC 10 H 6 NH 2 red:
BUT 3 SC 6 H 4 NH 2 + HNO 2 + C 10 H 7 NH 2 → BUT 3 SC 6 H 4 N \u003d NC 10 H 6 NH 2 + 2H 2 0
A mixture of α-naphthylamine with sulfanilic acid as a specific reagent for nitrites was first proposed in 1879 by the German chemist P. Griss. Later, this reaction was studied by the Hungarian chemist L. Iloshvay (Ilosvay). In modern analytical chemistry, this mixture is usually called the "Griess-Ilosvay reagent (reagent)" or simply "Griess reagent", and the corresponding reaction is called the "Griess-Ilosvay reaction" or "Griess reaction". Instead of α-naphthylamine, naphthols are also used.
Chugaev’s reagent, dimethylglyoxime, is often used as a specific reagent for nickel ions Ni 2+, which, in the presence of Ni 2+ cations in an ammonia medium, forms a red complex, poorly soluble in water, nickel bisdimethylglyoximate (II), which is traditionally called nickeldimethylglyoxime:
Dimethylglyoxime as a specific and very sensitive reagent for nickel ions Ni 2+ was first proposed by the Russian chemist L.A. Chugaev in 1905 and later named after him ("Chugaev's reagent").
Very few specific analytical reagents and reactions are known.
selective reagents and reactions make it possible to detect ( simultaneously !) several substances or ions (for example, crystallographic reactions, when several types of crystals are simultaneously visible under a microscope). Much more such reagents and reactions are known than specific ones.
Group reagents and reactions (a special case of selective ones) make it possible to detect all ions of a certain analytical group (but at the same time their analytical effects are summed up).
So, for example, hydrochloric acid HCl and water-soluble chlorides (NaCl, KCl, NH 4 Cl, etc.) are group reagents for a group of cations consisting of monovalent silver ions Ag +, "univalent" mercury Hg 2 2+ and divalent lead Pb 2+ More precisely, chloride ions Cl - act here as a group reagent, forming with the indicated metal cations white precipitates of the chlorides of these cations that are slightly soluble in water:
Ag + + Сl -- → AgCl ↓
Hg 2 2+ + 2Cl -- → Hg 2 Cl 2 ↓
Pb 2+ +2Cl -- → PbCl 2 ↓
Similarly, sulfuric acid H 2 SO 4 and soluble sulfates (Na 2 SO 4, K 2 SO 4, (NH 4) 2 SO 4, etc.) are group reagents for the group of divalent calcium cations Ca 2+ , strontium Sr 2+ and barium Ba 2+. With the indicated cations, the sulfate anion SO 4 2-- (actually a group reagent) gives sulfates that are slightly soluble in water and precipitate as white precipitates:
Ca 2+ + SO 4 2-- → CaSO 4 ↓
Sr 2+ + SO 4 2-- → SrSO 4 ↓
Ba 2+ + SO 4 2-- → BaSO 4 ↓
There are group reagents for other groups of cations and anions, as well as organic compounds that have the same functional group in their structure (for example, an amino group, a hydroxy group, etc.).
The main types of chemical reactions in analytical chemistry: acid-base, complex formation, oxidation-reduction. Used processes: precipitation-dissolution, extraction, sorption. Equilibrium constants of reactions and processes. State of substances in ideal and real systems. Structure of solvents and solution. Solvation, ionization, dissociation. Behavior of electrolytes and non-electrolytes in solutions. Debye-Hückel theory. Activity coefficients. concentration constants. Description of complex equilibria. Total and equilibrium concentrations. Conditional constants.
The rate of reactions in chemical analysis. Elementary steps of the reaction. Kinetic equations. Factors affecting speed. Catalysts, inhibitors. autocatalytic reactions. Induced and coupled reactions. inductive factor. Examples of acceleration and deceleration of reactions and processes used in chemical analysis.
Acid-base reactions . Modern concepts of acids and bases. Bronsted-Lowry theory. Equilibrium in the system acid - conjugate base and solvent. Acidity and basicity constants. Acid and basic properties of solvents. Autoprotolysis constant. Influence of the nature of the solvent on the strength of acids and bases. Leveling and differentiating effect of the solvent.
Acid-base balance in multicomponent systems. Buffer solutions and their properties. buffer capacity. Calculation of the pH of solutions of uncharged and charged acids and bases, polybasic acids and bases, mixtures of acids and bases.
Complex formation reactions. Types of complex compounds used in analytical chemistry. Classification of complex compounds according to the nature of the metal-ligand interaction, according to the homogeneity of the ligand and the central ion (complexing agent). Properties of complex compounds of analytical significance: stability, solubility, color, volatility.
Stepwise complexation. Quantitative characteristics of complex compounds: stability constants (gradual and general), formation function (average ligand number), complexation function, degree of complex formation. Factors affecting complex formation: structure of the central atom and ligand, concentration of components, pH, ionic strength of the solution, temperature. Thermodynamic and kinetic stability of complex compounds.
Influence of complex formation on the solubility of compounds, acid-base balance, redox potential of systems, stabilization of various degrees of oxidation of elements. Methods for increasing the sensitivity and selectivity of analysis using complex compounds.
Theoretical foundations of the interaction of organic reagents with inorganic ions. Influence of their nature, arrangement of functional-analytical groups, stereochemistry of reagent molecules on its interaction with inorganic ions. Theory of analogies of the interaction of metal ions with inorganic reagents such as H 2 O, NH 3 and H 2 S and oxygen-, nitrogen-, sulfur-containing organic reagents. The main types of compounds formed with the participation of organic reagents. Chelates, intercomplex compounds. Factors that determine the stability of chelates The most important organic reagents used in the analysis for the separation, detection, determination of metal ions, for masking and unmasking. Organic reagents for organic analysis. Possibilities of using complex compounds and organic reagents in various methods of analysis.
Redox reactions. Electrode potential. Nernst equation. Standard and formal potentials. Connection of the equilibrium constant with standard potentials. The direction of the oxidation and reduction reaction. Factors affecting the direction of redox reactions. The concept of mixed potentials. Mechanisms of redox reactions.
The main inorganic and organic oxidizing and reducing agents used in the analysis. Methods of preliminary oxidation and reduction of the determined element.
Precipitation and co-precipitation processes . Equilibrium in the solution-precipitate system. Precipitation and their properties. Scheme of sediment formation. Crystalline and amorphous sediments. Dependence of the sediment structure on its individual properties and conditions of sedimentation. Dependence of the precipitate shape on the rate of formation and growth of primary particles. Factors affecting the solubility of precipitates: temperature, ionic strength, action of the ion of the same name, reactions of protonization, complexation, redox, structure and particle size. Conditions for obtaining crystalline precipitates. Homogeneous precipitation. Sediment aging. Causes of sludge pollution. Classification of different types of co-precipitation. Positive and negative value of the co-precipitation phenomenon in the analysis. Features of the formation of colloid-dispersed systems. The use of colloidal systems in chemical analysis.
