ModuleII. Types of reactions and processes in analytical chemistry
Topic 4. "Main types of chemical reactions in analytical chemistry"
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.
4.1. Acid-base reactions. Modern ideas about 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. 4.2. 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 complex formation. 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 for 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. Chelate Stability Factors Critical organic reagents used in analysis for separation, detection, detection of metal ions, masking and unmasking. Organic reagents for organic analysis. Possibilities of using complex compounds and organic reagents in various methods of analysis. 4.3. 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. 4.4. 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. Module III. Detection and identification methods Topic 5. "Methods of detection and identification" 0.2 (8 hours) Tasks and selection of a method for the detection and identification of atoms, ions and chemical compounds. Fractional and systematic analysis. Physical methods for the detection and identification of inorganic and organic substances. Microcrystalloscopic analysis, pyrochemical analysis (flame coloring, sublimation, pearl formation). Drip analysis. Analysis by trituration of powders. Chromatographic methods of qualitative analysis. Express qualitative analysis in the factory and in the field. Examples of practical application of detection methods. ModuleIV. Methods for isolation, separation and concentration Topic 6. "Methods of isolation, separation and concentration" 0.1 (4 hours) The main methods of separation and concentration, their role in chemical analysis, selection and evaluation. Combination of separation and concentration methods with determination methods; hybrid methods. Single and multi-stage separation processes. Distribution constants. Distribution coefficient. Degree of extraction. Separation factor. concentration factor. 6.1. Extraction methods. Theoretical foundations of methods. Distribution law. Classification of extraction processes. extraction rate. Types of extraction systems. Extraction conditions for inorganic and organic compounds. Reextraction. Nature and characteristics of extractants. Separation and concentration of elements by extraction method. The main organic reagents used to separate elements by extraction. Selective separation of elements by selecting organic solvents, changing the pH of the aqueous phase, masking and unmasking. 6.2. Precipitation and co-precipitation methods. Application of inorganic and organic reagents for precipitation. Separation methods by precipitation or dissolution at various pH values, due to the formation of complex compounds and the use of redox reactions. Group reagents and their requirements. Characteristics of sparingly soluble compounds most commonly used in analysis. Concentration of trace elements by coprecipitation on inorganic and organic carriers (collectors). 6.3. Other Methods. Electrochemical methods. Distillation (distillation, sublimation). Zone melting. Topic 7. Chromatographic methods of analysis 0.2 (6 hours) 7.1. 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. Resolution as a factor in optimizing the chromatographic process. Qualitative and quantitative chromatographic analysis. 7.2. Gas chromatography. Gas-adsorption (gas-solid-phase) and gas-liquid chromatography. Sorbents and carriers, requirements for them. separation mechanism. Diagram of a gas chromatograph. Columns. Detectors, their sensitivity and selectivity. Applications of gas chromatography. 7.3. Liquid chromatography. Types of liquid chromatography. Benefits of High Performance Liquid Chromatography (HPLC). Scheme of a liquid chromatograph. Pumps, columns. Main types of detectors, their sensitivity and selectivity. 7.3.1. Adsorption liquid chromatography. Normal-phase and reversed-phase options. Polar and non-polar stationary phases and principles of their choice. Modified silica gels as sorbents. Mobile phases and principles of their choice. Applications of adsorption liquid chromatography. 7.4. Ion exchange chromatography. Structure and physico-chemical properties of ion exchangers. ion exchange equilibrium. Selectivity of ion exchange and factors determining it. Fields of application of ion-exchange chromatography. Ion chromatography as a variant of high performance ion exchange chromatography. Features of the structure and properties of sorbents for ion chromatography. One-column and two-column ion chromatography, their advantages and disadvantages. Ion chromatographic determination of cations and anions. Ion pair and ligand exchange chromatography. General principles. mobile and stationary phases. Areas of use. 7.5. size exclusion chromatography. General principles of the method. mobile and stationary phases. Features of the separation mechanism. Determined substances and areas of application of the method.7.6. Planar chromatography. General principles of division. Methods for obtaining planar chromatograms. Reagents for their manifestation. Paper chromatography. separation mechanisms. moving phases. Advantages and disadvantages. Thin layer chromatography. separation mechanisms. Sorbents and mobile phases. Areas of use.ModuleV. Chemical methods of analysis
Topic 8. "Chemical methods of analysis" 8.1. Gravimetric method of analysis. Essence of gravimetric analysis, advantages and disadvantages of the method. Direct and indirect methods of determination. The most important organic and inorganic precipitants. Errors in gravimetric analysis. General scheme of definitions. Requirements for precipitated and gravimetric forms. Changes in the composition of the precipitate during drying and calcination. Thermogravimetric analysis. Analytical balance. The sensitivity of the scales and its mathematical expression. Factors affecting weighing accuracy. Weighing technique. Examples of practical application of the gravimetric method of analysis. 8.2. Titrimetric methods of analysis. Methods of titrimetric analysis. Classification. Requirements for the reaction in titrimetric analysis. Types of titrimetric determinations. Methods for expressing concentrations of solutions in titrimetry. Equivalent, molar mass equivalent, molar concentration. Primary and secondary standards. Fixanals. Types of titration curves. Factors. affecting the nature of the titration curves and the magnitude of the titration jump in various methods. Equivalence point. Methods for determining the end point of titration in various methods.8.3. Acid-base titration. Construction of titration curves. Influence of the value of acidity or basicity constants, concentration of acids or bases, temperature on the character of titration curves. Acid-base titration in non-aqueous media. Acid-base indicators. Titration errors in the determination of strong and weak acids and bases, polybasic acids and bases.8.4. Redox Titration . Construction of titration curves. Influence of hydrogen ion concentration, complex formation, solution ionic strength on the character of titration curves. Methods for determining the end point of the titration. Titration errors. Methods of redox titration. Permanganatometry. Determination of iron(II), manganese(II), oxalates, hydrogen peroxide, nitrites. Iodometry and iodimetry. The iodine-iodide system as an oxidizing or reducing agent. Bromatometry, cerimetry, vanadatometry, titanometry, chromometry. Primary and secondary standards. Used indicators. Determination of inorganic and organic compounds. 8.5. Oprecipitation titration. Construction of titration curves. Methods for determining the end point of the titration; indicators. Titration errors. Application examples . 8.6. Complexometric titration. Inorganic and organic titrants in complexometry. The use of aminopolycarboxylic acids in complexometry. 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. Determination of calcium, magnesium, iron, aluminum, copper, zinc in solutions of pure salts and in the joint presence. 8.7 Other titrimetric methods of analysis. Thermometric, radiometric titration. Essence of methods. 8.8. Kinetic methods of analysis. Essence of methods. Catalytic and non-catalytic variants of kinetic methods; their sensitivity and selectivity. Types of catalytic and non-catalytic reactions used: oxidation-reduction, exchange of ligands in complexes, transformations of organic compounds, photochemical and enzymatic reactions. Methods for determining the concentration according to kinetic measurements. ModuleVI. Electrochemical methods of analysis Topic 9. Physico-chemical and physical methods of analysis. Electrochemical methods of analysis 9.1. Electrochemical methods of analysis. General characteristics of the methods. Classification. electrochemical cells. Indicator electrode and reference electrode. Equilibrium and non-equilibrium electrochemical systems. Phenomena arising from the flow of current (ohmic voltage drop, concentration and kinetic polarization). Polarization curves and their use in various electrochemical methods. 9.1.1. 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. Potentiometric titration. Change in electrode potential during titration. Methods for detecting the end point of titration in reactions: acid-base, complex formation, oxidation-reduction; precipitation processes. 9.2. Coulometry. Theoretical foundations of the method. Faraday's law. Methods for determining the amount of electricity. Direct coulometry and coulometric titration. Coulometry at constant current and constant potential. External and internal generation of coulometric titrant. Titration of electroactive and electrically inactive components. Determination of the end point of the titration. Advantages and limitations of the coulometric titration method compared to other titrimetric methods. 9.3. Voltammetry. indicator electrodes. Classification of voltammetric methods. Obtaining and characterization of the current-voltage curve. Limit diffusion current. Polarography. Ilkovich equation. Ilkovich-Heyrovsky polarographic wave equation. half wave potential. Identification and determination of inorganic and organic compounds. Modern types of voltammetry: direct and inversion, alternating current; linear sweep chronoamperometry (oscillography). Advantages and limitations compared to classical polarography. Amperometric titration . The essence of the method. indicator electrodes. Selection of the potential of the indicator electrode. Types of titration curves. 9.4. Other electrochemical methods of analysis. General characteristics of electrogravimetric methods. Electrical conductivity of solutions and principles of conductometry. Chronopotentiometry - voltammetry at direct current. Practical application of methods. Comparative characteristics of sensitivity and selectivity, areas of application of electrochemical methods.
ModuleVII. Spectroscopic methods of analysis
Topic 9. Physico-chemical and physical methods of analysis. Spectroscopic methods of analysis 9.15. Spectroscopic methods of analysis. The spectrum of electromagnetic radiation. 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. The basic laws of absorption of electromagnetic radiation (Bouguer) and the law of radiation (Lomakin-Sheibe). The relationship of the analytical signal with the concentration of the determined compound. Apparatus. Ways of monochromatization of radiant energy. Classification of spectral instruments and their characteristics. Radiation receivers. Instrumental interference. Noise and signal-to-noise ratio; evaluation of the minimum analytical signal. 9.16. Methods of atomic optical spectroscopy. Atomic emission method. Sources of atomization and excitation: electric discharges (arc, spark, reduced pressure), flames, plasma torches, inductively coupled plasma, lasers; their main characteristics. Physical and chemical processes in the sources of atomization and excitation. Spectrographic and spectrometric methods of analysis, their features, fields of application. Qualitative and quantitative analysis by flame emission spectrometry. Basic equipment: spectrographs, quantometers. Flame photometers and spectrophotometers. Metrological characteristics and analytical possibilities. Atomic fluorescent method. The principle of the method; features and application. Atomic absorption method. Atomizers (flame and non-flame). Radiation sources (hollow cathode lamps, continuous spectrum sources, lasers), their characteristics. Spectral and physico-chemical interference, ways to eliminate them. Metrological characteristics, possibilities, advantages and disadvantages of the method, its comparison with the atomic emission method. Examples of practical application of atomic emission and atomic absorption methods. 9.17. Methods of atomic x-ray spectroscopy X-ray spectra, their features. Methods of generation, monochromatization and registration of X-ray radiation. Types of X-ray spectroscopy: X-ray emission, X-ray absorption, X-ray fluorescence. Principle of X-ray emission spectroscopy; X-ray spectral microanalysis (electronic probe). Fundamentals of X-ray fluorescence spectroscopy; features and significance of the method (fast non-destructive multi-element analysis); examples of using. 9.18. Methods of molecular optical spectroscopy9.18.1. Molecular absorption spectroscopy (spectrophotometry). Relationship between the chemical structure of a compound and the absorption spectrum. Functional analysis on vibrational and electronic spectra. Communication of optical density with concentration. Basic law of light absorption. The main causes of deviation from the law (instrumental and physico-chemical). The concept of the true and apparent molar absorption coefficient. Methods for obtaining colored compounds. Photometric analytical reagents; requirements for them. Methods for determining the concentration of substances. Measurement of high, low optical densities (differential method). Analysis of multicomponent systems. Application of the method to study reactions in solutions (complex formation, protolytic, aggregation processes), accompanied by a change in absorption spectra. Metrological characteristics and analytical capabilities. Examples of practical application of the method. 9.18.2. Molecular luminescent spectroscopy. Classification of types of luminescence according to sources of excitation (chemiluminescence, bioluminescence, electroluminescence, photoluminescence, etc.), mechanism and duration of luminescence. Fluorescence and phosphorescence. Yablonsky's scheme. Stokes-Lommel law. Levshin's mirror symmetry rule. Factors affecting the luminescence intensity. Luminescence quenching. Spectral and physico-chemical interference. Quantitative analysis by luminescent method. Metrological characteristics and analytical capabilities of the method. Comparison of the possibilities of molecular absorption and luminescence spectroscopy in the determination of inorganic compounds. Advantages of luminescent spectroscopy in the identification and determination of organic compounds.
ModuleVIII. Analysis of specific objects
Topic 10. Analysis of objects10.1. The main objects of analysis Environmental objects: air, natural and waste water, precipitation, soil, bottom sediments, . Characteristic features and tasks of their analysis. Biological and medical objects. Analytical tasks in this area. Sanitary and hygienic control. Geological objects. Analysis of silicates, carbonates, iron, nickel-cobalt ores, polymetallic ores. Metals, alloys and other products of the metallurgical industry. Determination of ferrous, non-ferrous, rare, noble metals and analysis of their alloys. Analysis of non-metallic inclusions and determination of gas-forming impurities in metals. Control of metallurgical productions. Inorganic compounds. Substances of special purity (including semiconductor materials, high-temperature superconductivity materials); determination of impurity and alloying microelements in them. Layer-by-layer and local analysis of crystals and film materials. Natural and synthetic organic substances, polymers. Types of analysis of such objects and corresponding methods. Examples of solving problems of organic production control. As a result of studying the discipline, the student must: know: metrological foundations of chemical analysis, principles of sampling, types of chemical reactions and processes in analytical chemistry, basic methods of qualitative analysis, isolation, separation and concentration, selection of the appropriate method depending on the subsequent analysis, basic methods of quantitative analysis. be able to:
abstract a scientific text, calculate metrological characteristics, compare methods of analysis in terms of accuracy, selectivity, sensitivity and the minimum detectable content of a substance; select the minimum and representative sample, select the optimal process for analysis, conduct a qualitative chemical analysis of the sample, mask interfering ions, concentrate the analyte and separate mixtures, determine the quantitative composition by classical analysis methods, analyze the sample using modern electrochemical methods, including ion-selective sensors , to determine the qualitative and quantitative composition by modern optical methods, to analyze specific objects by the most optimal methods.own: methods of classical chemical analysis and modern physical and chemical analysis, skills in working with electrochemical, spectroscopic instruments, sample preparation for various analysis methods. Types of educational work: lectures, practical and laboratory classes, abstract, calculation tasks
The study of the discipline ends score and exam.
Discipline abstract
Analytical chemistry
The total labor intensity of studying the discipline is 18 credit units (648 hours)
The tasks of studying the discipline: the development of communicative and socio-cultural abilities and qualities; mastering the skills and abilities of self-improvement. Structure of the discipline (2)
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The tasks of studying the discipline: to acquire practical knowledge of the most important factors, events and phenomena from the history of Russia
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Tasks, principles, directions of development of gymnasium education at the present stage Kolesnikova V. I. director of the gymnasium No. 2
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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. Characteristic 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: preparation of a substance for analysis, taking an average sample, dissolving solids, preliminary tests, analysis of cations and anions.
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 - Iloshvaya (Iloshvaya), 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 that is 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 white precipitates of the chlorides of these cations that are sparingly soluble in water with the indicated metal cations:
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.).
Physico-chemical and physical methods used to detect elements. Answers the question - what substances are included in the object. The purpose of qualitative analysis is the detection of certain things or their components in the analyzed object. Reactions should be as selective as possible (with several components) and highly sensitive. Qualitative analysis in aqueous solutions is based on ionic reactions and allows the detection of cations or anions. If the object is new, nothing is known about it, then at the beginning a qualitative analysis is performed, and then a count. Precipitation of a white precipitate: . Main types of chemical reactions in analytical chemistry Key words: acid-base, complexation, redox. Analytical reactions- they are accompanied by ext. visual appearance (precipitation, coloration, outgassing). Formation of colored solutions: Fe (3+) + 3SCN (-) \u003d Fe (SCN) 3 (blood-red.) Objects can be in a solid state and liquid, i.e. "dry" and "wet" ways. Flame color: Na-yellow, K-violet, Rb-crimson, B-green, B-green, Pb-blue. "Wet" is more commonly used.
METHODS of qualitative analysis are divided into chemical, physico-chemical and physical. Physical Methods based on the study of physics. St. in the analyzed thing-va. These methods include spectral, etc. In physicochemical methods the course of the reaction is fixed by measuring a certain physical. Holy Island of the investigated r-ra. These methods include polarography, chromatography, etc. .To chemical methods include methods based on the use of chem. sv-in the investigated things-in. In chem. quality methods. analysis, only the analyte is used. reactions. Analytical reactions - they are accompanied by ext. visual appearance (precipitation, coloration, outgassing). Precipitation of a white precipitate: . Ways: objects can be in a solid state and liquid. "Dry" - coloration of the flame, the formation of free metals, etc. Flame color: Na-yellow, K-violet, Rb-crimson, B-green, Pb-blue. "Wet" is more commonly used. Depending on the number of objects n.:macroanalysis0,1, microanalysis
fractional method is based on the discovery of ions by specific reactions carried out in separate portions of the test solution. All cations are divided into 3 groups, including, respectively, s-, p- and d-elements. In fractional analysis, specific reactions are used that allow one ion to be detected in the presence of all other ions. There are few specific reactions. Systematic method- this is the sequential separation of ions and their discovery. It is based on the fact that, first, with the help of group reagents, a mixture of ions is divided into groups and subgroups, and then each ion is detected in these subgroups by special reactions. The fractional method is better than the systematic method in that it can save reagents and time. But since there are few specific reactions and the influence of interfering ions cannot be eliminated, then one turns to a systematic method of analysis.
The performance of each analytical reaction requires compliance with certain conditions for its implementation, the most important of which are: the concentration of the reactants, the medium of the solution, and the temperature. For example, in order for any precipitate to form, it is necessary, with the help of a certain reagent, to create conditions under which a supersaturated solution is obtained. In the presence of an excess of the reagent, the reaction may not be completed and continue. For example, when Hg2+ ions are detected using KI according to the reaction Hg(N03)2 + 2KI → 4HgI2 + 2KN03, in the case of an excess of the KI reagent, instead of a bright red precipitate of Hgl2, a pale yellow solution is formed: HgI2 + 2KI - + K2.
Sensitivity of a chemical reaction- the smallest amount of a substance that can be detected by this reaction or quantified by this method of analysis. Highly sensitive district-requires a small amount of in-in Insensitive reaction-p-tion requiring large contents. analysis. in-a. The reaction is called specific when it allows one ion to be detected in the presence of all the others. Specific, for example, for the ammonium ion is the reaction: NH4Cl + KOH → NH3 + KCl + H2O. The sensitivity of qualitative reactions is influenced by factors such as Ammonia is detected by the smell or by the blue color of a red litmus paper soaked in water and placed over a test tube. Selective reactions (selective) - reactions with multiple components.
Vreactions-change in concentration in-va in units. time (mol / l * sec) concentration continuously changes in time, then the rate continuously changes in time. Factors affecting the reaction rate: -1) the nature of the reactants; -2) The concentration of the reagents. Mass action law: the rate of a homogeneous reaction at each moment of time is proportional to the product of the concentration of the reacting substances raised to a certain power. V direct reaction = K [A] ^ a * [B] ^ b, where - ref. molar concentr. in-in., K-speed constant. Each reaction has its own rate constant. The reaction order can take arbitrary values..3) Dependence on temperature. The rate of most reactions increases with increasing temperature, because. the number of active particles increases.
Chemical equilibrium- the state of a chemical system in which one or more chemical reactions reversibly proceed, and the rates in each pair of forward-reverse reactions are equal to each other. For a system in chemical equilibrium, the concentrations of reagents, temperature, and other parameters of the system do not change with time. A2 + B2 ⇄ 2AB. Equilibrium constant shows how many times the speed is straight. reaction\u003e or 1-the direct line prevails if the Physical meaning is K: the reaction rate at a concentration of reacting in-in 1 mol / l. Depends on the nature of in-in and t. Does not depend on concentration. Straight*[A]^a*[B]^b=Cobr.[C]^c*[D]^d
Z. mass action shows how to change the reaction in the right direction. Need to enlarge. rate of forward reaction and reduce-reverse. FeCl3+NH4SCN↔Fe(SCN)3(blood red)+3NH4Cl.
10) EQUILIBRIUM CONSTANT, the ratio between the concentrations of reaction products and starting substances, which characterizes the CHEMICAL EQUILIBRIUM of a REVERSIBLE REACTION at a certain temperature. The type of K. equilibrium depends on the type of chemical. reactions. 1) acid-base reactions - acids and bases are used. K. equilibrium is used only for weak acids and bases. For weak to-t: HA=H^+ +A^- Kequal=[H]*[A]/ For strong acids: BOH=B+OH Keq=[B]*/ 2) sedimentation (heterogeneous systems) KA(precipitate, solid)=K^+ +A^-(saturation, liquid) Keq=[ K]*[A]/ 3) the formation of complex Comm. Keq=Kimage. complexes=
Kravn. r-tion = Knestability complex. For multi-stage chem. reactions n. track. balance: A+3B=AB3. 1st stage: A+B=AB Keq=[AB]/[A]*[B] 2nd stage: AB+B=AB2 Keq=/*[B] 3rd stage: AB2+B=AB1/3 Total balance K:: A + 3B \u003d AB2 K total. equal = / [A] *.
Conclusion: To the general equal chemical reaction = the product of steps. K.equal
11) Kravn. depends on t for the glass effect reaction. Exothermic - with the release of heat, when hanging t, the equilibrium shifts to the left, i.e. The coefficient of the direct reaction decreases. Endothermic - with absorption of heat from outside. environment, with an increase in t, the equilibrium shifts to the right, i.e. Direct response crev increased. For a reaction that does not go with a thermal effect, Cequiv does not depend on t.
12) The general equilibrium constant is equal to the product of step constants. General chem.reaction::A+3B↔AB3-multi-stage reaction.: 1) step A + B ↔ AB Equal \u003d / [A] * [B]. 2) step AB + B ↔ AB2 Equal \u003d / * [B]. 3) stage AB2+B↔AB1/3. General reaction: A+3B↔AB2. K total. equal = / [A] *. General Kravn allows you to determine the direction of the chemical. reactions. An example of the dissolution of Fe sulfide in acid: FeS+2H^+= Fe^2++H2O. Stage 1: FeS↔Fe^2++S^-. Kravn=*/. K1==* Stage 2: S^2++2H+↔H2S. Crav=/Kdis.H2S. Ktot.=K1*K2=PRFeS/Kdis.H2S. The greater the PR of the precipitate and the smaller the Kdis of the forming electron, the more complete the direct reaction (dissolution of the precipitate)
13) Electrolytes, in-va, in which ions are present in a noticeable concentration, causing the passage of email. current (ionic conductivity). Weak electrolytes include many organic acids and bases in aqueous and non-aqueous solvents. The degree of dissociation depends on the nature of the solvent, the concentration of the solution, temperature, and other factors. The same electrolyte at the same concentration, but in different solvents, forms solutions with different degrees of dissociation. Oswald's dilution law: with a decrease in the concentration of the solution, the degree of dissociation of a weak electrolyte increases.
14) Electrolytes, substances in which ions are present in a noticeable concentration, causing the passage of email. current (ionic conductivity). There are strong and weak ones. Strong electrolytes are almost completely dissociated into ions in dilute solutions. These include many inorganic salts, acids and bases that have a high dissociating ability. The concentration of ions in solutions of strong electrolytes is so high that interionic interaction forces begin to appear. Properties of the electrolyte, depending on the number of ions, are less pronounced in this case. The activity of an ion (denoted as a) is related to its concentration by the ratio: a = fC. where f is activity factor and she. Chem. the activity of each ion depends on the concentration of all ions and charges. The larger these values, the less chem. the activity of each ion. Coef. the activity of ions depends on the composition and concentration of the solution, on the charge and nature of the ion, and on a number of other conditions.
15) There is no general theory of acids and bases. For analytical purposes
use the Arrhenius theory of acids and bases. According to this theory, acids are cat substances. give away H cations, donars. Bases are substances cat attached., acceptors. In protolithic theory acids are proton donors, i.e. in-va, giving off protons. Acids are denoted by the letter a. CH3COOH ↔ H+ +CH3COO-. The foundations in this theory are denoted by the letter b. You are founded. can be neutral-HCl, H2SO4; anionic-HCO3.HSO3; cationic-NH4. Neutral-HCl, Y2SO4; Anionic-YCO3, HSO3 ; Cationic-NH4.
16) In the expression Ko \u003d, where Ko naz . thermodynamic equilibrium constant, for ideal and non-ideal systems depends on t, pressure and the nature of the solvent. When presenting instead of activities of equilibrium concentrations Kp=[C]*[D]/[A]*[B] or K'= we obtain concentration equilibrium constants. The values of concentration constants are influenced by many factors: Ko and K'-t, pressure, the nature of the solvent (K is the real concentration equilibrium constant, they characterize the equilibrium position, taking into account the influence of electrostatic interactions, K' is the conditional concentration equilibrium constant, they characterize taking into account the total influence of electrostatic and chemical interactions). The concentration constants can be calculated from the thermodynamic ones by first calculating the coefficients. activity.
17) Hydrogen indicator - a value that characterizes the activity or concentration of hydrogen ions in solutions. The hydrogen index is denoted by pH. Hydrogen index numerically \u003d negative decimal logarithm of the activity or concentration of hydrogen ions, expressed in moles per liter: pH \u003d -lg [ H + ] neutral solution pH \u003d 7, acidic solution pH 7. In water, the concentration of hydrogen ions is determined by the electrolytic dissociation of water according to the equation H2O=H++OH-. The dissociation constant at 22°C is: 
Ionic product of water- the product of the concentrations of hydrogen ions H+ and hydroxide ions OH− in water or in aqueous solutions Acidity scale of solutions:
| pH | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 |
| RON | 14 | 13 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
| Reaction environments | strongly acidic | slightly acidic | Neutra- linen | Weak-slit | Strongly alkaline |
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| sour | alkaline |
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18) Acid-base indicators- organic compounds that can change color in solution with a change in acidity (pH). Universal indicator - a mixture of several indicators, they are impregnated with strips of "indicator paper", with which you can quickly determine the acidity of the studied aqueous solutions. Indicators are widely used in titration in analytical chemistry and biochemistry. 
Indicators are usually used by adding a few drops of aqueous solution. Another way to use is to use strips of paper impregnated with an indicator solution (eg "Universal Indicator").
To determine the pH value of solutions several methods are widely used. 1) The use of a special device - a pH meter - allows you to measure pH in a wider range and more accurately (up to 0.01 pH units. 2) Analytical volumetric method - acid-base titration. A solution of known concentration (titrant) is added dropwise to the test solution. When they are mixed, a chemical reaction takes place. Equivalence point is the moment when the reaction ends. 3) Influence of temperature on pH values
19) Salt hydrolysis- this is the interaction of salt ions with water with the formation of low-dissociating particles. a) Salt is formed by a weak acid and a strong base: pH> 7
b) A salt is formed by a strong acid and a weak base: pH c) A salt is formed by a weak acid and a weak base:
Protolytic equilibrium during the hydrolysis of salts, it can be shifted to the right or to the left with a change in temperature, dilution of the solution. Types of hydrolysis: cation hydrolysis (only the cation reacts with water); anion hydrolysis (only anion reacts with water); joint hydrolysis (both cation and anion react with water).
20) Salt hydrolysis- this is the interaction of salt ions with water with the formation of low-dissociating particles. Factors affecting the hydrolysis of salts: -nature of salt; - salt concentration; -t (the more >t, the more >h); - pH of the medium. Hydrolysis of salts reduces their activity in a qualitative analysis. 1) (NH4) 2CO3-group reagent 2gr. cation
concentr. ammonium carbonate decreases and the activity of the reagent decreases. 2) (NH4) 2S-group reagent 3gr. cation
The activity of ammonium sulfide is reduced. Application:- detection of BiCL3+H2O ↔Bi(OH)2CL+HCL ions; Bi(OH)2CL →BiOCL+H2O. Types of hydrolysis: hydrolysis by cation (only cation reacts with water); anion hydrolysis (only anion reacts with water); joint hydrolysis (both cation and anion react with water).
21) Salt hydrolysis- this is the chemical interaction of salt ions with water ions, leading to the formation of a weak electrolyte. Hydrolysis can aid the reaction and sometimes interfere with the analysis. There are the following ways to suppress and enhance the hydrolysis of salts.1. The addition of another electrolyte to a salt solution, to-you or basic .. To enhance the hydrolysis of salts, bases are added to bind during the hydrolysis of H + ions. The equilibrium of the reaction shifts towards the hydrolysis of the salt. To suppress the hydrolysis of these salts, k-you are added to the solution, then: salt hydrolysis decreases.
22) Salt hydrolysis is a chem. the interaction of salt ions with water ions, leading to the formation of a weak electrolyte. Salt hydrolysis is a reversible chemical reaction. Its quantitative characteristics are the degree of hydrolysis (h) and the hydrolysis constant (Kg). h- shows what part of the salt has been hydrolyzed, i.e. turned into its components; measured in% or fractions of a unit. The degree of hydrolysis is not constant. Kg is the equilibrium constant of the reversible reaction. Depends on t, but does not depend on the concentration of the solution. Kg \u003d K (H2O) / K diss.k-you * K diss. Degree of hydrolysis is the ratio of the number of hydrolyzed molecules to the total number of dissolved molecules; h= (Сhydr/Сtot) 100%, where Сhydr is the number of moles of hydrolyzed salt, Сtot is the total number of moles of dissolved salt. The degree of salt hydrolysis is higher, the weaker the acid or base that forms it. Hydrogen index, pH- a measure of the activity of hydrogen ions in a solution, and quantitatively expressing its acidity, is calculated as a negative (taken with the opposite sign) decimal logarithm of the activity of hydrogen ions, expressed in moles per liter: pH \u003d -Lg
23) buffer systems called r-ry, preserved. Constant pH, when added to solution or when diluted with strong to-t or bases. The ability to maintain a constant pH value . buffer action. There are: a) acidic - from weak to-t and their salts (acetate); b) basic - from weak bases and their salts (ammonia). One component neutralizes the added to-that, the second - in the added alkali. Buffers can be acidic, alkaline or neutral, eg phosphate buffer, carbonate buffer. For an acidic buffer: pH = pKk-you-LgSk-you / Salt. For alkaline buffer: pH=14-pKosn+LgCosn/Salts. Buffers are two component systems. Buffer solutions are needed to create pH. Each buffer has a pH.
24) Each buffer has a pH depending on the concentration of the component and their volumes. pH(sour buffer.) = pKk-you-Lg * Nu to-you / Nu salt. pH (alkaline buffer) \u003d 14-pKosn. + Lg * Nu basic / Nu salt
Acetate buffer: CH3COOH ↔ CH3COO+H CH3COONa ↔ CH3COO+Na
1. Add a small amount of NaOH (strong alkali)
NaOH+CH3COOH → CH3COONa+H2O
2. Add a small amount of HCL (strong to-ta)
HCL+CH3COONa ↔ CH3COOH+HCL
3. Add a small amount of NaOH (alkali)
NaOH(strong)+NH4C(very weak)L→ NH4OH+NaCL
4. Add a small amount of HCL (strong acid)
HCL (strong) + NH4OH (salt) ↔ NH4CL + H2O. Buffers can be acidic, alkaline or neutral. Examples of buffers: 1) phosphate NaH2PO4 (weak acid) and Na2HPO4 (salt)
H2PO4 ↔ H+HPO4
Na2HPO4 → 2Na+HPO4 2) carbonate NaHCO3-weak acid and Na2CO3-salt
Each buffer has a certain capacity. When large amounts of acids and bases are added to a buffer, its pH may change. Buffer tank is the number (mol) of a strong acid or a strong base that must be added to 1 liter of buffer to change its pH by 1. The greater the concentration of the component, the greater the buffer capacity. The optimal ratio between the components is 1: 1
25) Buffers are two-component systems. The most common are acetate and ammonia. It is used to create and maintain substances. In addition, buffer solutions are widely used in chemical analysis and for the calibration of pH meters. Buffer solutions play a huge role in the life of organisms, ensuring the constancy of blood and lymph pH. .And in the quantitative analysis at opred. water hardness. (ammonia buffer) formula: W \u003d N * V1 / V
26) Chem. equilibrium- the state of the system in the cat. the rate of the forward reaction = the rate of the reverse. The displacement is based on the action of the masses. CH3COOH ↔ CH3COO+H (equivalent system)
We introduce a salt of acetic acid into the system
CH3COONa ↔CH3COO+Na(strong electrolyte)
After introduction into the salt solution, the concentration of acetate increases. The rate of the reverse reaction increases, the equilibrium shifts to the left, the dissociation of acetic acid decreases, and it becomes a weaker electrolyte.
27) Heterogeneous systems- heterogeneous, equal-phase systems, they consist of two phases. In qualitative analysis, heterogeneous systems consist of liquid (phase 1), solid (phase 2) and sediment. Phase- aggregate state (liquid, solid and gaseous). Heterogeneous are used in qualitative analysis for detection, for the separation of substances, and also in quantitative analysis. Applications for heterogeneous systems: 1) Precipitation and dissolution of precipitation 2) Evaporation and evaporation, distillation.
ETC.- the product of molar K ions of the precipitate in a saturated solution. Solubility product-constant of a heterogeneous process sol. The greater the solubility of the precipitate, the greater the product of the precipitate . Solubility(mol / l) - the concentration of a slightly soluble substance in a saturated solution under these conditions.
28) The purpose of qualitative analysis: detection of things-in. Most often they are besieged. Therefore, you need to know the condition for their precipitation: 1) the solubility of the in-in. The lower the solubility of the precipitate, the greater the completeness of the precipitation. , if the concentration does not exceed 10^-6 mol/l. 2) Quantity of precipitant. The greater the concentration of the precipitant, the greater the completeness of precipitation. 3). The degree of dissociation of the precipitant. It is advisable to use a strong electrolyte precipitant. He is more active. NH4-weak electrolyte and NaOH-strong electrolyte
Mg+NaOH → Mg(OH)2+2Na
The completeness of precipitation wakes up more.
NH4OH ↔ NH4+OH
NaOH ↔ Na+OH 4)pH-p-ra
Each precipitate falls at a certain pH-r-ra, this allows you to separate the ions. 5). The presence of foreign electrons in the solution. Foreign electrolytes-do not contain identical ions with precipitants and with a precipitated ion.
Example:
29) The solubility of a sparingly soluble compound. depends on the presence in the solution of strong electrolytes that do not have a common ion with the precipitate and have a common ion. The presence of a strong electrolyte that does not have an ion of the same name with the precipitate increases solubility by reducing the activity of ions in the solution. This phenomenon is called the salt effect. Salt effect- increasing the solubility of precipitation with an extraneous electrolyte. Example: The p-value of BaSO4 in 0.1 M KNO3 increases by 2.2 times.
30 ) To dissolve the precipitate, it is necessary to make a solution over the precipitate of unsaturated. This is achieved by: 1) diluting - adding water. This method is used for highly soluble precipitates. 2) gas evolution FeS ↓ + 2HCl → FeCl2 + H2S Keq. \u003d PR (FeS) / Kdiss. H2S >> 1-reaction proceeds 3) Formation of weak electrolytes 4) OVR (change in the charge of ions in the solution) To the balance of dissolution of the precipitate, if Krav.> 1, dissolution occurs.
31) Complexation is widely used in both qualitative and quantitative analysis, because they are colored.
Complex compounds is a complex group; noun. In the solution as a whole, differing in St. from the components that form it. The complex includes: center. Atom and legends. central atom- a particle around which the legends are located. Ligands-can be anions (chlorine, boron, iodine) the composition of the molecule can include organic and inorganic. comp. Example: ^2+ CI2 Donor ligands e.
32) Redox reactions are widely used in analytical chemistry in both qualitative and quantitative analysis. Oxidation is the donation of electrons. Recovery-application of electrons. The oxidizing agent accepts electrons and passes into the reducing form. The reducing agent, giving up electrons, passes into the oxidizing form, therefore, for each oxidizing agent, respectively. conjugate reducing agent or vice versa.
Types of OVR: 1) Intermolecular - reactions in which oxidizing and reducing atoms are in molecules of different substances, for example: H2S + Cl2 → S + 2HCl 2) Intramolecular - reactions in which oxidizing and reducing atoms are in molecules of the same substance , for example: NH4NO3 → N2O + 2H2O. The stronger the oxidizing agent, the weaker the conjugated reducing agent. They are used in chemical. analysis method.
33) Sorption processes- based on absorption by a solid or liquid from a solution or from a gas. Things that absorb other things called. sorbent .(substance) Sorption is subdivided into: - adsorption - absorption of a substance on the surface; - absorption - absorption of a substance by the volume of the sorbent. The greater the concentration of the substance, the greater the sorption. Sorbents are divided into molecular (absorb molecules) and ion-exchange (absorb ions). The extraction efficiency determines the coefficient. distribution. K distribution = C in-va (in the organic phase) / C in-va (in the aqueous phase) Extraction- absorption, dissolution of one component. It can be used to separate and concentrate cations and anions.
1) The task of the number of analysis is the determination of the content of the analyzed thing in the object. The content can be expressed in terms of: 1) for solids - w (in-va) in the object, g / t, mg / kg; 2) for liquids - w (in-va) in solution, mol / l, g / l, etc.
The task of analytics chemistry, including the number of analysis in determining the things that include one or another element, this is phase analysis. For example: Si can be in the form of SiO2, AI2O3*SiO3.
Methods: chemical (based on chemical reactions), physical (on the study of the physical properties of substances depending on their composition.), chemical-physical (on the study of the physical properties of substances obtained in a chemical reaction).
2) There are: systematic, random, misses. Systematic can be provided:
Methodical (errors depending on the instruments and the frequency of reagents)
Operational Errors – Do not perform the analysis in a timely manner.
Random errors - no pattern, cannot be foreseen (temperature, humidity)
Misses are gross errors (incorrect calculation, sifting the solution).
Errors can be absolute and relative.
Absolute - the difference between the received and the true result.
Relative - the mass of the absolute error to the true result.
3.) The method is based on weighing ref. objects and received at chemical. reactions in-in on the analyte. scales. Weighing accuracy per analyte. weights = 2*10^-4. The method is accurate, but very time consuming. It is used in the analysis of wine, milk, etc. It is divided into: - settling method (based on the settling of things - in their filtration, washing and drying); and - distillation method (based on the removal of volatile substances by heating or by treatment with reagents).
Precipitation Requirements: Must have low solubility, quickly filter and wash away impurities.
Requirements for the precipitator: The precipitant must completely precipitate the component. Requirements for weight it's a sediment cat. weigh out ): the composition of the weight form must exactly match its chemical. formula and must withstand high temperatures and chem. stable.
4.) co-precipitation- simultaneous precipitation of several substances. There is surface (absorption of things in the sediment surface) or external and internal co-precipitation (mechanical capture of sediment particles by a part of the solution).
Ways to reduce co-precipitation: sediment re-precipitation, sediment washing. Application of co-precipitations: To increase the concentrations of microcomponents, to detect substances Mg + 2OH Mg (OH) 2, some precipitates can absorb indicators, while the color of the indicator changes.
5) 1. The presence of extraneous electrolytes (temperature, pH of the medium, nature of the solution). The presence of a salt effect. 2. With increasing temperature, the solubility of most precipitates increases. 3. Influence of pH: The solution of precipitation depends on the pH of the medium. The pH of the precipitation depends on the pH of the indicators. 4. Influence of the nature of the solvent. 5. the presence of foreign substances
6.)
Conversion factor F-ratio molar. mass determined. in-va and molar. masses of the weight form. F=x*M def..shape/y*M weight.shape. Where x and y are numbers equalizing the number of atoms in the numerator and denominator. In the method of sedimentation, there are: 1) the determined form - the analyzed content. 2) precipitated form-sediment, which is precipitated and 3) weight-sediment, which is weighed. m(def. form)=F*m(weight form)*100%/m sample. Eg: Fe(def. form) →Fe(OH)3 ↓(precipitable form)→Fe2O3(weight form).
7)
volumetric method- based on measuring the volume of the solution that reacted with another solution. For analysis, you must have: the analyzed solution, the titrant solution is a solution with an exact known concentration, and titration is the gradual addition of one solution to another solution until the end of the solution. One solution is added to the titration flask and the other solution is added to the burette. Then one solution is titrated with another. Advantage of the method: the method is fast, but less accurate than the weight method. The task of analysis is to accurately establish the equivalence point.
8) The method is based on the neutralization reaction H3O+ OH↔ 2H2O
The method is used to separate acids, bases, salts having an acidic or alkaline reaction. Equivalent point- the moment of the end of the reaction. It is determined by the change in color of the titrated solution. One of the fixing methods is the indicator method. Indicators - substances due to which it is possible to establish the end point of equivalence (the moment of a sharp change in the color of the titrated solution).
9). Pipetting method. A portion of the analyzed substance is dissolved in a volumetric flask, diluted with water to the mark, the solution is mixed, an aliquot of the solution is taken with a pipette and titrated. You need to measure 3 times. Take the average volume of solution that went for titration. Single weight method. Take separate, close in size sample of the analyzed in-va. Dissolve in an arbitrary volume of water and completely titrate the resulting solutions. The error should not exceed 0.1%
10.)
Acid-base indicators- These are soluble complex organic compounds that can change their own color depending on the pH of the solution. By chemical nature, they are weak acids or bases, partially dissociating in solution. Acid-base indicators, as a rule, are reversible indicators that can reversibly change color depending on the pH of the solution.
Chromophore theory explains the color of the indicators. Ionic theory suggests the presence in the solution of two forms of the indicator molecule - an acidic form, and a basic form
11) The prepared solutions are prepared from an accurate sample of a chemically pure substance and its solutions in a certain volume of water. standard. Standardized- their concentration is determined by standard solutions. These include unstable substances. Titer-shows the mass determined. in-va interacting with 1 ml of this solution. Molar massequivalentssubstances- mass of one pray equivalents, equal to the product of the equivalence factor by molar mass this substances. Substance equivalent - a molecule or part of it is detached. or join 1 singly charged ion. H+ and OH-
12) Titration curves- show the change in the pH of the solution during titration. Used to select an indicator. There is a sharp pH jump on the curve, the moment the reaction ends. The pH jump starts at a higher pH and ends at pH=10. Weak to-you strong fundamentals. T.e. at pH = 8.9, the phenolphthalein indicator is used. it changes color at pH=8-10. One of the fixing methods is the indicator method. Indicators are substances by which it is possible to establish the end point of equivalence (the moment of a sharp change in the color of the titrated solution).
13) Titration of polybasic acids or polyacid bases has several equivalence points, and accordingly the pH curve gives several inflections, in most cases, however, not sharply pronounced. Polybasic acids (H3PO4, H2CO3) dissociate stepwise. For example: H3PO4↔ H2PO-4 + H+, H2PO-4 ↔
HPO2-4 + H+, (HPO^-2)4 ↔PO3-4 + H+.
this is a titration curve for 0.1 H3PO4 with 0.1 M NaOH
titration curves of polybasic acids have several inflections corresponding to different stages of dissociation. With m-about to-that is titrated as monobasic. With f-f it is titrated as dibasic.
14) The method is based on precipitation. Precipitation titration methods: argentometry (AgNO3 titrant), rhodanitometry (NH4SCN titrant), mercurometry (Hg2(NO3)2 titrant)
More method: the simplest of all methods of argentometry and at the same time quite accurate. Used in neutral or slightly alkaline media. Its essence lies in the direct titration of a liquid with a solution of silver nitrate with an indicator of potassium chromate. AgNO3+K2CrO4(indicator) → Ag2CrO4.↓(red)+2KNO3. The Mohr method is widely used in food analysis. . Folgard method: used in acidic environments. Based on the titration of a solution containing silver ions with standard solutions of NH4NCS or KNCS: Ag+ + NCS- ↔ AgNCS↓. Fe3+ ions are the indicator in this method. Adsorption indicators- Substances capable of being adsorbed on the surface of the sediment and changing the color or intensity of luminescence.
16)titrantIndicator- chem. in-va, changing color, forming a precipitate when the concentration of any component in the solution changes. Ex. 2 types: 1) react with an oxidizing agent or resurrect with a color change Eg. Starch (indicator, colorless) + I2 → I2 * starch (blue color). 2) changes its color depending on the RH potential. A) Permanganatometry - KMnO4 titrant, acidic medium. MnO4+5e+8eH→Mn^2++4H2O (fe=1/5). B) Chromatometry-titrant K2Cr2O7, acid medium. Cr2O7+6e+14H→2Cr^3++7H2O (fe=1/6) all resurrections. C) Iodometry-titrant I2. KI. Na2SO3+I2+H2O→2I+Na2SO4. Used in the analysis of resurrections. D) Bromatometry-titrant Br2 C6H5OH+3Br2→C6H2Br3OH+3HBr. It is used very rarely. E) Bromatometry-titrant NaBrO3. 2BrO3+6H+5e→Br2+3H2O (fe=1/6)
17))titrant- a reagent with a precisely known titer (concentration). Indicator- chem. in-va, changing color, forming a precipitate when the concentration of any component in the solution changes. W \u003d N * V * 1000 / V (H2O), where N is the normality of the solution, V is the volume of the solution. Water hardness is measured in mg * eq / l. We determine the hardness using Trilon B. Complexometry is based on the reactions of the formation of soluble complex compounds. Complexometric titration is subdivided into complexometry and mercurymetry. The basis of these methods is the reaction between defined. in-m and reagent, and as a result of this reaction, complex compounds are formed (this is a compound that consists of a complexing agent and ligands, which are surrounded near it).
18) Based on the movement of charged particles in an electric field. The particles are in the liquid. Particles move in an electric field
at different speeds. Cathode-negatively charged e; anode positive. Neutral particles will also go to the electrode, but more slowly. The speed of the particles depends on their charge and on the mobility, and the mobility of the particles depends on the size of the particles. The larger the charge of the particles and the smaller their size, the faster they move. It is used for the analysis of all organic. and inorganic. in-in Classification: zonal electrophoresis and capillary. Zonal electrophoresis is used in the analysis of milk, and capillary electrophoresis in the analysis of wine. PICTURE
19) There are direct and indirect. Based on the measurement of email. parameters depending on the composition of the p-ra Most of them are based on electrolysis. Can be measured next. parameters: resistance and electrical conductivity of the solution, current strength, electrode potential. Electrochem. methods are divided into: conductometry, potentiometry, volammetry, culometry, electrogravimetry. Conductometry includes methods that measure the electrical conductivity of electrolytes. Potentiometry is based on measuring the potential of the indicator electrode. (The electrode is a sensor). voltage. Coulometry is based on the measurement of the amount of electricity. Electrogravimetry - on the electrolysis of the analyzed solution el. current.
20) The method is based on the electrical conductivity of the solution. In coductrometry, the resistance of the solution is measured in special. electrolytic cells. Conductometry is subdivided into direct and conductometric titration. . Conductometric titration- This is an indirect method, serves to define. equivalence points. Used to define equivalence points, using a graph, cat. shows the dependence of the electrical conductivity of the solution on the volume of the titrant. T. equivalence- the moment of titration, when the number of equivalents of the added titrant is equal to the number of equivalents of the determined substance in the sample.
21) Based on the measurement of the potential of the indicator electrode .. (electrode-sensor ). Indicator.electrode-electrode, potential cat. depends on the composition of the analysis. solution. The absolute potential of the electrode cannot be measured. delta E (electrode potential) \u003d E (ind.) - E ^ 0 To measure the potential of the electrode, potentiometers are used, they consist of two electrodes. Indicator electrodes are: electrodes, on the surface of the cat. there is an exchange of electrons and electrodes, where there is an exchange of ions. Potentiometric. titration is based on measuring the potential of the indicator electrode during titration. The equivalence point can be seen by a sharp jump, for this you need to build a graph and see it.
22) Coulometry is based on the measurement of the amount of electricity spent on the electroconversion of a certain substance. There is also indirect culometry or culometric titration based on the interaction of the analyzed substance with the titrant. Voltammetry is based on the radiation of the dependence of the current on the external. voltage. For this method, 2 indicator and standard electrodes are used. Coulometry is good because it is not obligatory to use standard solutions. The formula for the amount of electricity: Q (coulomb) = I (current) * tau (analysis time).
23) The method of separation and analysis of in-in, based on the distribution between two phases that do not mix - mobile and immobile. The stationary phase is a solid, and the mobile phase is a liquid or gas that passes through the stationary phase. What is good about chromatography is that you can repeat the processes many times. This method is universal, i.e. separation and determination of solid, liquid and gaseous Comm. Any sorption process xp-Xia distribution constant Kraspred.=Snepodv.*Sdvizh. Columns in chromatography have a diameter of 4-6mm. Ion exchange chromatography is a liquid chromatography for the separation of cations and anions. This chromatography is used for example for water purification. There is also paper chromatography, but it is bad in that it is slowly divided and a large number of substances cannot be taken at once.
24) Based on the exchange of ions between the mobile and stationary phases (ion exchanger) There are also cation exchange resin (exchanged cations), anion exchange resin (anions) and ampholyte (exchanged anions and cations). Ionites are natural and natural and also artificial. It is used to separate cations, separate electrolytes from non-electrolytes, and even in the analysis of wine and milk. Sorbents- solids or liquids that are absorbed from the environment. Medium gases. There are absorbents-forms a solution with absorbed water and adsorbents- absorb in-in. There are solid sorbents, a cat. divided into faceted and fibrous.
25) Based on interaction analysis. in-va with electromagnetic radiation. Each in-in, when interacting with radiation, forms a spectrum. Spectrum-ordered by wavelength electromagnetic radiation. Resonance- matching frequencies. Types of radiation: X-ray, UV, IR, radio waves, magnetic field. Atoms and molecules are able to absorb, emit and scatter radiation. Spectral methods are subdivided into atomic and molecular methods. Atomic is based on the interaction of atoms with electromagnetic radiation, it is subdivided into atomic emission and atomic absorption analysis. Emission is emission, emission. Molecular spectra-electromagnetic spectra of emission and absorption. GRAPHICS2
26) Based on the ability to define. in-va, a component of the mixture to absorb electromagnetic radiation. There are photometric and spectrophotometric methods. The photometric method is measured by a photometer, and the spectrophotometric method is measured by a spectrometer. There is h. Bouguer absorption: D=-LgT= E*L*c, where D is the density of the solution, T is the transmission, L is the thickness, c is the concentration. From this z. it follows that the higher the concentration of the solution, the higher the density of the solution. Usually, in photometric analysis, the intensity of radiation is compared. On the calibration graph, the dependence of the density of the solution on its concentration is built, and according to this graph, the his concentration.
27) These two methods are based on the measurement of light intensity. Turbidimetry-method of analysis of turbid media. Used for analytics. definitions in different environments. But this method is not very accurate, and is only used to determine components where high accuracy is not needed. Nephelometry- used to determine chlorides (AgCl) and sulfates (BaSO4).
28) Atomic emission-is based on the emission of electromagnetic radiation by atoms, the cat is placed in a flame. The essence of the method: the analyzed solution in the flame of a gas burner. Used in metallurgy. This method is based on the fact that the atoms of each element can emit light of certain wavelengths, but in order for the atoms to begin to emit light, they need to be excited, the more atoms are excited, the brighter the radiation will be. This method is very accurate. Atomic absorption- based on the absorption of light. This method is also used in metallurgy, for most metals. The method is good because it is very simple, but you cannot use several elements at the same time.
29) Based on the phenomenon of luminescence. This method is used in organic chemistry, it allows you to detect in-va in mixtures. There are fluorescent (this method is not very selective), phosphorescent analysis (it has high selectivity) Selectivity-this is the property of one in-va to select the property of another in-va.
30) This method uses X-ray spectra for chem. analysis in-in. With it, you can determine the qualitative and number of analysis. It is based on the fact that when an atom is excited, electrons are removed from the inner shells. Electrons from external shells jump to empty spaces, releasing excess energy in the form of a quantum. And according to the number of these quanta, it is possible to determine the number and qualitative analysis.
31) Refractometry is a method for studying things, based on the determination of the refractive index of light. It is used for defining physical-chem. parameters in-in. n is the refractive index. Coef. refraction: n = sin (alpha) / cos (beta) It is used to determine the composition and in-in, as well as for the quality of chemical. composition in products. Polarimetry-based on the degree of light emission. This method is used in analytical chemistry, in the analysis of essential oils and for the study of radiation. All measurements are carried out with polarimeters.
32) Nuclear magnetic resonance is the resonant absorption of the electromagnetic energy of things. This phenomenon was discovered in 1945. It is used in physical chem. analysis methods. The main part of the spectrometer is a magnet, a cat. placed in a vessel between the poles of an electromagnet. Then this vessel begins to rotate. When the magnetic field begins to increase, they begin to cut the nuclei to which the spectrometer is tuned. These readings are recorded and rotated as quickly as possible.
33) IR spectrometry- based on absorption of IR light. When IR light is absorbed in the molecule, vibrational and rotational movements are enhanced. Application-def. qualitative and number analysis. ultraviolet- the method is based on the absorption of v-m ultraviolet radiation. The course of the analysis: UV light is passed through the solution, each molecule absorbs a certain amount. light.
34) Mass spectrometry is a physical a method for measuring the ratio of the mass of charged particles of matter to their charge. With the help of this method, new drugs are being developed for indistinguishable diseases. It is used with illegal distribution of drugs. Nuclear energy is unthinkable without mass spectroscopy. To get a mass spectrometer, you need to turn molecules into ions, then these ions need to be transferred to the gas phase in a vacuum, a vacuum is needed so that the ions move without obstacles, and if there is no vacuum, then the ions turn into uncharged particles.
35) EPR - absorption of energy by things containing paramagnetic particles. Based on the interaction of a thing with a magnetic field. Used to study paramagnetic particles, widely used in chemistry. EPR - a special case of magnetic resonance Underlies the radio spectroscopic. research methods of the substance The essence of the EPR phenomenon lies in the resonant absorption of electromagnetic radiation by unpaired electrons. EPR was discovered by Zavoisky in 1944.
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 ideas about 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 complexation 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. Chelate Stability Factors Critical organic reagents used in analysis for separation, detection, detection of metal ions, 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.
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