Department of Analytical Chemistry, Moscow State University. Department of Analytical Chemistry, Faculty of Chemistry, Moscow State University

We all deal with chemical analysis all the time. For example, in a clinic or, alas, in a hospital. If you think about it, other examples of analysis will come naturally. To ensure that tap water is suitable for drinking, its composition is carefully controlled. Determine soil acidity. Assess blood sugar levels in diabetics. What about detection of alcohol vapors in the air exhaled by the driver? What about monitoring the chlorine concentration in a swimming pool? These are all examples of important and necessary chemical analyses.

Millions of similar analyzes are done. In principle, mass tests of this kind can be done by not very qualified people. But under one obvious condition: you need to have appropriate methods and means for analysis (means here do not mean money at all, but instruments, reagents, dishes, etc.). But methods and means are invented and developed by specialists of a completely different level, scientific analysts. These specialists are trained by the best universities.

The Department of Analytical Chemistry of Moscow State University is one of the most famous centers for such training. But it is also a major scientific center where very interesting research is being conducted. The department is popular among students of the Faculty of Chemistry. The demand for graduate analysts is very high.

Among the employees of the department is the head of the department, academician Yu.A. Zolotov, Deputy Head, Corresponding Member of the RAS O.A. Shpigun, eight more professors. All of them are leading scientists in their fields, widely known specialists. The department has an Analytical Center of the Faculty, the All-Russian Ecological and Analytical Association, three small enterprises, and joint laboratories with instrument-making companies. The department teaches analytical chemistry at 8 faculties.

But the most important thing, the most interesting thing is the scientific problems solved at the department. Here, original methods of chemical analysis are successfully developed, problems of analysis of environmental, biomedical, and technical objects are solved. The laboratory has many modern instruments, which are used by graduate and postgraduate students, and often junior students, not to mention regular employees.

Isn’t it interesting to create methods that make it possible to detect harmful elements in natural water, to separate complex mixtures of organic compounds into individual components, or to diagnose pulmonary diseases by the composition of exhaled air? Much is being done at the department on the chemical analysis of various types of materials, especially semiconductor materials.

Groups of scientists, led by young doctors and candidates of science, work at the forefront of science, in a businesslike, creative, friendly environment.

Head of the department: academician

The department's staff includes 80 employees, including 17 doctors and 30 candidates of science. The department has six research laboratories and a workshop in analytical chemistry.

About 100 articles are published annually in domestic and international (about 20%) journals, and more than 120 abstracts of reports. Employees of the department make presentations (more than 100 per year) at Russian and international (about 30%) conferences.

The course of analytical chemistry at the Faculty of Chemistry is studied in the 3-4 semester (2nd year), includes lectures, seminars, and practical classes. At the end of the 3rd semester, a test task is submitted, at the end of the course (4th semester) - an exam and defense of the course work. Based on the rating results, it is possible to get an “automatic” - excellent and good.

From the history of the department

In connection with the reform of higher education, on August 13, 1929, a resolution was adopted by the Council of People's Commissars of the USSR on the reorganization of chemical departments of physics and mathematics faculties of universities into independent chemical faculties. In fact, the Faculty of Chemistry was established in 1930 and among the first five departments it included the Department of Analytical Chemistry. The head of the department was prof. A.E. Uspensky, who headed the department until 1931. Within the framework of the department, a laboratory of analytical chemistry was formed, the head of which was Associate Professor E.S. Przhevalsky.

Many outstanding scientists worked at the Department of Analytical Chemistry. Professor K.L. Malyarov, who was engaged in microanalysis during the restoration period and in the first years of industrialization. Microanalysis was also carried out by E.S. Przhevalsky and V.M. Peshkova. Since 1934, Peshkova began research on the use of new organic reagents in analytical practice (in particular, she developed a method for the quantitative determination of nickel by reaction with dimethylglyoxime). Z.F. Shakhova expanded research on the use of complex compounds in chemical analysis. V.M. Shalfeev conducted research on electrical analysis.

Educational and scientific work at the department began in full after moving to a new building in 1953. I.P. was invited to head the department. Alimarin. Since 1989, Yu.A. became the head of the department. Zolotov. Yu.A. Zolotov is a recognized specialist in the field of analytical chemistry and metal extraction. He introduced (1977) the concept of hybrid methods of analysis. In 1972, the State Prize was awarded for the development of the theory and new physical and chemical methods for the analysis of high-purity metals, semiconductor materials and chemical reagents. He was the first in the country in the 1980s to develop work on ion chromatography (the most important result is the use of amphoteric amino acids as eluents (1985) and the reduction of the detection limit through the use of
conductometric detector).

Heads of the department:
1929-1931 – prof. A.E. Uspensky
1933-1953 – prof. E.S. Przhevalsky
1953-1989 – academician I.P. Alimarin
since 1989 – academician Yu.A. Zolotov

Department laboratories:

Concentration laboratory
academician, prof. Yu.A. Zolotov

V.R.S. group G.I. Cizina
group of prof. E.I. Morosanova
group of prof. S.G. Dmitrienko
V.R.S. group I.V. Pletneva

Chromatography laboratory
corresponding member RAS, prof. O.A. Shpigun

group of assistant professor E.N. Shapovalova
V.R.S. group A.V. Pirogov
V.R.S. group A.V. Smolenkova
educational work of the chromatography laboratory

Laboratory of Spectroscopic Analysis Methods
Doctor of Chemical Sciences, Prof. M.A. Proskurnin

group of assistant professor A.G. Borzenko
group of prof. V.M. Ivanova
group senior researcher N.V. Alova
group of prof. M.A. Proskurnina
group of assistant professor A.V. Garmash

Laboratory of Electrochemical Methods
Doctor of Chemical Sciences, Prof. A.A. Karyakin

group of prof. A.A. Karjakin
group of assistant professor A.I. Kameneva
group of assistant professor N.V. Swedes

Laboratory of Kinetic Analysis Methods
Doctor of Chemical Sciences, Prof. T.N. Shekhovtsova

group of prof. T.N. Shekhovtsova
V.R.S. group M.K. Beklemisheva

Academician Yu.A. Zolotov

ABOUT THE DEPARTMENT OF ANALYTICAL CHEMISTRY

The department was created together with the Faculty of Chemistry in 1929 on the basis of the laboratory of organic and analytical chemistry of the Faculty of Physics and Mathematics, which existed at Moscow University since 1884. The department was headed: in 1929 - 1931. - Professor A.E. Uspensky, in 1931-1953. - Professor E.S. Przhevalsky, in 1953-1989. - Academician I.P. Alimarin. Since 1989, the department has been headed by Academician Yu.A. Zolotov.
Currently, the department has over 80 employees (6 doctors, 42 candidates of science).

Prehistory

Chemical analysis was introduced into academic courses at least throughout the 19th century. In 1827, university employee A.A. Iovsky published the book “Chemical Equations with a Description of Various Methods for Determining the Quantitative Content of Chemical Substances.” Before the revolution, analytical chemistry was taught at the university by outstanding chemists: V.V. Markovnikov, M.M. Konovalov, I.A. Kablukov, N.M. Kizhner, N.A. Shilov, N.D. Zelinsky. However, the training of professional analytical chemists began later; the first thesis on analytical chemistry was defended in 1928 by V.V. Ipatiev.

Scientific services in the field of chemical analysis have been carried out since the first years of the existence of Moscow University; the first chemical laboratory opened in 1760. At the end of the 18th century, much attention was paid to the detection and determination of precious metals (“assay chemistry”), then to the analysis of mineral waters (F. Schmidt, 1807-1882). In the second half of the 19th century, the university began to frequently carry out analyzes for industry, mainly on orders from Moscow manufacturers.

Among the works of a later period, which can already be considered scientific, urine analysis should be noted (book by V.S. Gulevich, 1901). After the revolution, a lot of effort was spent on analyzing chemical reagents, the production of which was being established in the country. This work was carried out for a long time in collaboration with the Institute of Reagents (IREA). Future leading employees of the department, E.S., grew up in research on the analytical chemistry of pure reagents, in which it was necessary to determine impurities. Przhevalsky, V.M. Peshkova and others. Professor K.L. Malyarov carried out work on microchemistry and analytical hydrochemistry.

At the end of the 20s, when the department was created, analytical chemistry used mainly chemical (“wet”) methods - gravimetric (then called gravimetric), titrimetric (volume), and classical methods of gas analysis. On a very small scale, some physicochemical and physical methods were used - conductometry, potentiometry, colorimetry, spectral analysis. True, mass spectroscopy, polarography, micromethods of organic elemental analysis were already known (the 1923 Nobel Prize to the Austrian scientist F. Pregl), even chromatography, but they were not widely used.

It is very significant that at the end of the last - beginning of this century the theoretical basis of “solution”, “wet” analytical chemistry was formed. The beginning was made by W. Ostwald in his book (1894) “Scientific Foundations of Analytical Chemistry”. This theoretical foundation was based mainly on the doctrine of chemical equilibrium in solutions (law of mass action, electrolytic dissociation, solubility product, etc.).

From the history of the department

After the formation of the department, the Faculty of Chemistry, the entire university, and the entire system of higher education in the USSR were subject to various restructurings and reorganizations for some time. However, in the pre-war years the situation stabilized.

An important place at the department in the pre-war, war and early post-war years was occupied by its head, Evgeniy Stepanovich Przhevalsky, who for some time was also the dean of the Faculty of Chemistry and the director of the Scientific Research Institute of Chemistry of Moscow University, which existed until 1953. Other leading employees and teachers of those times - V.M. Peshkova, N.V. Kostin (also a dean), P.K. Agasyan. The teaching work was well done, but scientifically the department may not have occupied a leading position at that time.

In 1953, Professor Ivan Pavlovich Alimarin, who later became an academician, was invited to head the department. Under his leadership, and Ivan Pavlovich served as head for 36 years, the department became one of the leading centers for research in the field of analytical chemistry.

Academician Alimarin (1903-1989) was the most famous analytical scientist in our country. He contributed to the analysis of mineral raw materials, radiochemical analytical methods, new methods of separation of substances; paid a lot of attention to organic analytical reagents. I.P. Alimarin headed the Scientific Council of the USSR Academy of Sciences on Analytical Chemistry for a long time, was the editor-in-chief of the Journal of Analytical Chemistry, and worked at the International Union of Theoretical and Applied Chemistry. The academician was elected their honorary doctor by three foreign universities; he was a foreign member of the Academy of Sciences of Finland (see the book: Ivan Pavlovich Alimarin. Articles. Memoirs. Materials. M.: Nauka, 1992).

The main directions of scientific work of the department in the 50-80s. - determination of impurities in inorganic substances, including highly pure ones; organic analytical reagents; extraction of metal ions; ion exchange, then extraction chromatography; polarography, potentiometry; atomic emission analysis, later laser spectrometry, kinetic methods, and partly gas analysis.

The works of professors A.I. were famous. Buseva, V.M. Peshkova, V.M. Ivanov and others on organic analytical reagents, Professor P.K. Agasyan, associate professors E.N. Vinogradova, Z.A. Gallai on electrochemical methods, associate professor N.I. Tarasevich on spectral analysis. Professor Yu.Ya. Kuzyakov, N.E. Kuzmenko and F.A. Gimelfarb, who headed after N.I. Tarasevich laboratory of spectroscopic methods, each brought something new to this area.

Many teaching aids and manuals have been published.

Graduates of the department have occupied and continue to occupy leading positions in research institutes, universities, and partly in enterprises of the country; Some of the graduates also work abroad.

Analytical chemistry today

Currently, analytical chemistry as a field of science is no longer just a part of chemistry; it is turning into a large independent mega-discipline. This is mainly due to the powerful expansion of the arsenal of analysis methods, including chemical, physical, and biological. A new general theory is being developed, including, for example, analytical metrology.

The capabilities of chemical analysis have increased sharply in terms of sensitivity and speed. Many methods allow you to simultaneously determine several dozen components. Analyzes without destroying the analyzed sample, at a large distance, in a flow, at a single microscopic point or on a surface, are becoming commonplace. Mathematization and computerization have significantly expanded the capabilities of known methods and made it possible to create fundamentally new ones.

Analytical chemistry and analytical services solve, or should solve, many vital problems in the state and society. This includes control of production processes, diagnostics in medicine (blood, urine analysis, etc.), monitoring of environmental objects, meeting the needs of the military, criminologists, and archaeologists.

Main areas of research at the department

If we talk about objects of analysis, about the scope of application of methods and means of chemical analysis, then now environmental objects, especially water, come first. Many of the department’s studies are aimed at creating new and effective ways to assess water quality, methods for determining impurities in natural or waste waters. Attention is also paid to other objects - biological, technological and others; for example, methods for analyzing semiconductor substances are being developed.

The department presents almost all modern methods of analysis. The main methods being developed are sorption and extraction concentration of inorganic and organic micro- and ultramicro-components, including methods carried out automatically in a flow; chromatographic methods for the separation of substances and their determination with various detectors, including mass spectrometry (liquid, including ion, gas chromatography); spectroscopic methods of analysis - spectrophotometric in the visible and ultraviolet regions of the spectrum, including the reflective version; luminescent; thermal lens spectrometry, etc.; electrochemical methods, especially voltammetry and direct potentiometry (ion selective electrodes); kinetic and enzymatic methods.

The department is well equipped. There are more than two hundred devices in the general workshop, and about a hundred in special workshops. The equipment park of scientific laboratories is very diverse and rich. Thus, among the spectral instruments are laser installations for thermal lens measurements from Coherent (USA), an electronic spectrometer from Leibold (Germany), X-ray fluorescence analyzers Spark and Spectroscan (Russia), a laser microprobe analyzer LAMMA (Germany), etc. The department has excellent chromatographic equipment, for example, capillary gas chromatographs, chromatomass spectrometer, supercritical fluid chromatograph, ion chromatographs from two companies, various liquid chromatographs. At the modern level, there are also electrochemical instruments - a voltammetric analyzer, polarographs and others, for example, installations for electrochemical research made in the USA and Switzerland. Other instruments for chemical analysis include a supercritical fluid extractor (Italy), a device for capillary electrophoresis (USA) and isotachophoresis (Slovakia-Russia).

Some scientific problems solved at the department

Let us consider, as an example, several works performed at the department in more detail.

Test methods. For centuries, since the time of the alchemists, chemical analysis has been carried out in laboratories. And now hundreds of thousands, millions of analyzes are carried out in analytical laboratories, and now not only chemical ones. However, recently the situation has been changing: chemical analysis is gradually moving to those places where the analyzed object is located - in the field, in the workshop, at the airport, to the patient’s bedside, even in ordinary apartments. The fact is that there is a huge need for non-laboratory analysis, and that it is now possible to create effective tools for such analysis “in situ”. These tools also include tools for test methods of chemical analysis.

Test methods of analysis are rapid, simple and relatively cheap methods for detecting and determining substances, usually not requiring significant sample preparation, the use of complex stationary instruments, laboratory equipment and general laboratory conditions, and most importantly, do not require qualified personnel.

The department is developing purely chemical and enzymatic test methods. Specially selected reactions and reagents are used in “ready” forms - on indicator papers, in the form of tablets, powders, indicator tubes, etc. By the intensity or tone of the color that appears during analysis or by the length of the colored layer in the tube, the desired component can be detected and quantified. Not only visual registration is possible, but also using the simplest pocket-type devices.

For example, an extremely sensitive enzymatic method has been created for the determination of mercury, especially in environmental objects. Or you can name a series of works in which indicator tubes were proposed for determining other heavy toxic metals in natural and drinking waters. Another simple means is tablets made of polyurethane foam (foam rubber), onto which analytical reagents are applied in advance or which can sorb the resulting colored reaction products from solution. The appearance or change in color on the tablets is compared with the scale. It is possible to determine phenols, surfactants, and a number of metal ions.

The methods for implementing test methods, as already mentioned, are very simple. However, this simplicity does not come cheap: achieving it requires good science to create the appropriate tools. Here, as always, the rule of inverse proportionality applies: to develop the simplest and most effective test tool, you need to invest maximum creative energy, ingenuity, knowledge, and a lot of money.

New approaches to the determination of organic toxicants in environmental objects. The content of more than a thousand substances in natural waters is standardized, many of which are toxic and carcinogenic. If the concentration of a substance is normalized, it must be controlled. This means that there must be reliable methods of such control for all these substances and corresponding means - instruments, reagents, reference materials, etc. This is an almost impossible task - the list of “controlled” components is very large. Indeed, in real practice, analysis is carried out on a maximum of 100-150 substances, and usually on a smaller number of components.

How to be?

The department is developing the idea of changing the analysis methodology itself. We are talking about abandoning attempts to follow the approach “each substance has its own methodology” in favor of systematic analysis with the widespread use of generalized indicators. For example, such generalized indicators may be the content of organic chlorine, phosphorus or sulfur in the analyzed object. It makes no sense to test water separately for dozens of possible toxic organochlorine compounds if the initial experiment showed that there is no organic chlorine in the sample at all. New methods for such “gross” analysis are being created, and they are very sensitive.

The best method for determining anions. This method is ion chromatography. The department was the first center in the former USSR where they began to develop this effective method of analysis. Now the corresponding laboratory has a large fleet of the most modern ion chromatographs. Accelerated methods are being developed for the simultaneous determination of 10-12 anions, the simultaneous determination of cations and anions in environmental objects, food products and other samples. A school of specialists in ion chromatography was formed, the first domestic symposium on this method was held, and books were written.

Ion selective electrodes (ISE). A feature of the department’s work in this direction is the creation of ISE for organic substances using complex formation according to the “guest-host” or “key-lock” scheme.

X-ray fluorescence analysis with concentration. XRF is a wonderful method. It allows you to simultaneously determine a large number of elements, with the exception of the elements at the beginning of the periodic table, without destroying the analyzed sample. But the method is not very sensitive; it is difficult to detect concentrations below 0.01 percent. Sorption concentration on cellulose filters comes to the rescue, and complex-forming atomic groups are grafted onto the cellulose. In this case, the detection limits are greatly reduced, and the X-ray fluorescence spectrometry method takes on a new meaning.

Use of enzymes. Immobilized enzymes are special and very effective analytical reagents: they provide high selectivity of interaction with the components being determined. Using the enzyme peroxidase, a very sensitive and selective method for the determination of mercury has been created.

Thermal lens spectroscopy. The setup used in this method takes up a lot of space and is by no means easy to use. However, the efforts to create the installation and maintain it in working condition are completely justified: compared to conventional spectrophotometry, the detection limits of substances can be reduced by 2-3 orders of magnitude!

Microwave sample preparation and other applications of microwave radiation. It is very interesting that such radiation can significantly accelerate many slowly occurring chemical analytical reactions. An example is the complex formation reactions of platinum metals: it is known that these metals often form kinetically inert complexes, the substitution of ligands in them occurs very slowly. In a microwave oven the picture changes dramatically; this has great implications for the practice of analysis.

Educational and methodological work

Employees of the department teach analytical chemistry to students of chemical, geological, geographical, biological, soil faculties, the faculty of fundamental medicine, the Higher College of Chemistry of the Russian Academy of Sciences, the Higher College of Materials Sciences, as well as students of schools with a chemical bias. This is a huge and very responsible job, it has produced excellent, knowledgeable teachers, including many young ones. The practical work on analytical chemistry is one of the best at the Faculty of Chemistry; students carry out numerous educational tasks, coursework with interest, and participate in annual competitions in analytical chemistry. During the year, about a thousand students of chemistry and related faculties pass through the general practicum, and over fifty 4th and 5th year students of the chemistry faculty pass through special practicums.

The general course of analytical chemistry, taught to 2nd year students of the Faculty of Chemistry, is accompanied by seminars and extensive, intense and very interesting laboratory work. In 1999, the second edition of a two-volume textbook written by members of the department, “Fundamentals of Analytical Chemistry,” was published. Various manuals, manuals, and problem books are constantly published.

Many chemistry students choose analytical chemistry as their area of specialization; in terms of the number of students admitted, the department ranks one of the first places in the faculty (from 20 to 40 third-year students annually). The training of analysts includes attending a large number of special courses, performing practical work, and speaking at seminars and conferences. Students receive good training in methods of concentration of substances, spectroscopic, electrochemical, chromatographic and other methods of analysis, become familiar with the metrology of chemical analysis in detail, and listen to lectures on general issues of analytical chemistry.

Every year 10-15 graduates of Moscow State University and other universities enter the department’s graduate school. Special courses are taught for graduate students, including elective courses.

The department annually awards graduate and undergraduate students a prize or scholarship named after I.P. Alimarina.

External relations of the department

The department closely cooperates with institutes of the Russian Academy of Sciences, especially with the Institute of General and Inorganic Chemistry named after. N.S. Kurnakov and the Institute of Geochemistry and Analytical Chemistry named after. IN AND. Vernadsky. In 1996, the Scientific and Training Center for Analytical Chemistry of Moscow State University was created. M.V. Lomonosov and the Russian Academy of Sciences; the center is based at the department.

The department is also the base of the All-Russian environmental analytical association "Ecoanalysts"; Numerous contacts in the field of environmental analysis are carried out through the association. The department, for example, actively participated in the implementation of projects under the “Ecological Safety of Russia” program and other environmental programs, and is one of the organizers of all-Russian conferences on the analysis of environmental objects.

Numerous joint scientific works are being carried out with a number of industry research institutes and universities in Russia. For example, for a long time the department has been closely cooperating with the Burevestnik Research and Production Association (St. Petersburg) in the field of X-ray spectral and electrochemical equipment.

International relations are carried out in several directions. There are joint research projects carried out within the framework of the INTAS program, as well as on the basis of bilateral agreements. Agreements are being implemented with instrument-making companies, as a result of which the department has the opportunity to have modern instruments without purchasing them. We can mention contacts with the companies Carlo Erba (Italy) and Biotronic (Germany) in the field of chromatography and chromatography-mass spectrometry, with the Milestone company (Italy) in the field of microwave technology, with the Intertech company (USA) on spectroscopic instruments.

In 1995, the department held the V International Symposium on Kinetic Methods of Analysis, and in 1997 – the International Congress on Analytical Chemistry.

ZOLOTOV YURY ALEXANDROVICH (b. 1932). Head of the Department of Analytical Chemistry (since 1989), full member of the Russian Academy of Sciences (1987), professor (1970), Doctor of Chemical Sciences (1966). Director of the Institute of General and Inorganic Chemistry of the Russian Academy of Sciences (since 1989), head of the laboratory of analytical chemistry of platinum metals of this institute. President of the Russian Chemical Society named after. DI. Mendeleev (1991-1995).

Areas of scientific research. Extraction of inorganic compounds, concentration of trace elements, flow analysis, test methods of analysis. Methodological problems of analytical chemistry.

Main scientific achievements. Developed the theory of extraction of metal chelates and complex acids; discovered, investigated and used in practice the phenomenon of suppression of the extraction of one element by another; proposed a number of new effective extractants; created a large number of extraction methods for separating complex mixtures of elements for the purposes of analytical chemistry and radiochemistry. He developed a general methodology for the concentration of microelements, proposed a number of concentration methods and used them in the analysis of high-purity substances, geological objects and environmental objects; Together with his colleagues, he created new sorbents for concentration purposes. Introduced the concept of hybrid methods of analysis (1975), developed a large number of such methods. He formed a broad scientific direction - the creation of test methods and corresponding means of chemical analysis. Organized research on ion chromatography and flow injection analysis.

The head of the department is a member of several international organizations, was or is a member of the editorial boards of major international journals in analytical chemistry, and is invited as a speaker at international conferences.

“Department of Analytical Chemistry Approved by the methodological commission of the Department of Analytical Chemistry A.V. Ivanov METHODOLOGICAL GUIDE TO QUALITATIVE AND QUANTITATIVE...”

Moscow State University named after M.V. Lomonosov

Chemical faculty

Department of Analytical Chemistry

Approved by the methodological commission

Department of Analytical Chemistry

A.V.Ivanov

METHODOLOGICAL GUIDE

BY QUALITATIVE AND QUANTITATIVE

ANALYSIS

FOR 2nd YEAR GEOGRAPHY STUDENTS

FACULTY

Edited by Professor V.M. Ivanov Moscow 2001 Introduction The methodological manual is intended as a guide to practical classes in the course “Qualitative and Quantitative Analysis” for 2nd year students of the Faculty of Geography, specializing in the Department of Soil Geography. The discipline program "Qualitative and Quantitative Analysis for the Faculty of Geography of Moscow State University" aims to study the theoretical foundations of chemical (titrimetric and gravimetric) and instrumental (spectroscopic and electrochemical) methods of analysis and familiarize themselves with the possibilities of their practical application. The methodological manual consists of three parts, the first includes a calendar of lectures and practical classes and questions for colloquiums. A rating scale for assessing knowledge according to the positions provided for in the curriculum is provided. The second part contains methods for conducting qualitative reactions of individual cations and anions, the third "Quantitative analysis" includes methods for gravimetric and titrimetric determination of a number of elements in pure solutions and in real objects. The theoretical foundations of the methods are briefly outlined. All proposed methods have been tested by laboratory assistants and engineers of the Department of Analytical Chemistry of Chemical Engineering faculty of Moscow State University.

The first part of the manual was compiled with the participation of Professor, Doctor of Chemical Sciences.

T.N. Shekhovtsova.

Comments and wishes of teachers and students will be received by the author with deep gratitude.

I. COURSE PROGRAM

The lesson schedule includes 14 lectures, 16 practical classes, 3 milestone tests (during lecture hours) and 3 colloquiums. At the end of the semester there is an examination.

Plan of lectures and tests Lecture 1 Subject and methods of analytical chemistry. Chemical balance.

Factors influencing chemical equilibrium.

Equilibrium constants.

Lecture 2 Acid-base balance.

Lecture 3 Calculation of pH in various systems Lecture 4 Chemical equilibrium in a heterogeneous system.

Lecture 5 Calculation of conditions for dissolution and precipitation of sediments. Calculation of solubility product from solubility data.

I milestone test "Acid-base equilibrium and equilibrium in a heterogeneous system."

Lecture 6 Complexation reactions. Complex connections.

Lecture 7 Organic reagents in analytical chemistry.

Lecture 8 Equilibrium in redox reactions.

Calculation of redox potentials.

Direction of oxidation-reduction reactions.

Lecture 9 Gravimetric method of analysis II milestone test "Redox reactions and complex formation reactions."

Lecture 10 Titrimetric methods of analysis, their application. Acid-base titration.

Lecture 11 Complexometric and redox titration.

Lecture 12 Metrological foundations of analytical chemistry. Statistical processing of analysis results.

III milestone test "Titrimetric methods of analysis, metrological foundations of analytical chemistry".

Lecture 13 Introduction to spectroscopic methods of analysis.

Lecture 14. Introduction to electrochemical methods of analysis.

Practical lesson plan

Lesson 1 Introductory talk on qualitative analysis. Qualitative reactions of cations of groups I-III: K+, Na+, NH4+, Mg2+, Ba2+, Ca2+, Pb2+ and anions: SO42-, CO32-, Cl-, NO3-, PO43 Qualitative reactions of cations of groups IV - VI: Al3+, Cr3+, Zn2+ , Fe2+, Lesson 2 Fe3+, Mn2+, Co2+, Ni2+, Cd2+, Cu2+.

Homework: calculating equilibrium constants.

Separation of a mixture of cations using paper chromatography. Conversation Lesson 3 on qualitative analysis schemes.

Homework: calculating pH in solutions of acids, bases, ampholytes and buffer mixtures.

Lesson 4 Test task No. 1: analysis of a mixture of cations of groups I-VI and anions (solution).

Homework: calculating the solubility of poorly soluble compounds, the formation of precipitation.

Test task No. 2: analysis of a solid mixture of cations and anions from Lesson 5, or a natural object.

Lesson 7 Colloquium No. 1: Chemical equilibrium. Acid-base balance. Equilibrium in a heterogeneous system.

Lesson 8- Introductory talk on gravimetry.

10 Test task No. 3: determination of sulfate ions in a mixture of sodium sulfate and sodium chloride.

Homework: complexation reactions;

calculation of redox potentials.

Lesson 11 Introductory talk on acid-base titration.

Preparation of solutions - primary standard solution of sodium carbonate (Na2CO3) and secondary standard solutions - hydrochloric acid (HCl) and sodium hydroxide (NaOH). Standardization of HCl and NaOH.

Lesson 12 Test task No. 4: determination of HCl.

Homework: constructing titration curves.

Lesson 13 Introductory talk on complexometric titration.

Control task No. 5 - complexometric determination of calcium and magnesium in their joint presence.

Lesson 14 Colloquium No. 2. Complexation reactions.

Organic reagents. Acid-base and complexometric titration.

Lesson 15 Introductory talk on redox equilibrium and titration. Preparation of a primary standard solution of potassium dichromate (K2Cr2O7) or oxalic acid (H2C2O4) and a secondary standard solution of potassium permanganate (KMnO4).

Test No. 6: determination of iron or water oxidability Lesson 16 Introductory conversation on the method of flame photometry. Determination of potassium and sodium.

Colloquium No. 3. Redox reactions.

– – –

Chemical equilibrium in a homogeneous system. Its main types:

acid-base, complexation and oxidation-reduction equilibrium. Factors affecting chemical equilibrium: concentrations of reacting substances, nature of the solvent, ionic strength of the solution, temperature.

Activity and activity coefficient. Total and equilibrium concentrations.

Competing reactions, competitive reaction coefficient.

Thermodynamic, real and conditional equilibrium constants.

Acid-base balance. Modern ideas about acids and bases. Basic provisions of the Bronsted-Lowry theory. Acid-base conjugate pairs. The influence of the nature of the solvent on the strength of acids and bases.

Autoprotolysis constant. Leveling and differentiating effects of the solvent. Buffer solutions. Calculation of pH of aqueous solutions of strong and weak acids and bases, ampholytes, buffer solutions.

Chemical equilibrium in a heterogeneous system. The main types of chemical equilibrium in a heterogeneous system: liquid-solid phase (solution precipitate), liquid-liquid. Equilibrium constant of the precipitation-dissolution reaction (product of solubility). Thermodynamic, real and conditional equilibrium constants. Conditions for precipitation and dissolution of sediments. Calculation of sediment solubility under various conditions.

Colloquium No. 2.

Complexation reactions. Organic reagents.

Acid-base and complexometric titration.

Complex compounds and organic reagents. Types and properties of complex compounds used in analytical chemistry. Stepwise complex formation. Thermodynamic and kinetic stability of complex compounds. The influence of complexation on the solubility of compounds and the redox potential of the system.

Theoretical foundations of the interaction of organic reagents with inorganic ions. Functional and analytical groups. The theory of analogies of the interaction of metal ions with inorganic reagents such as H2O, NH3, H2S and oxygen-, nitrogen-, sulfur-containing organic reagents. Chelates, intracomplex compounds. Use of complex compounds in analysis for detection, separation, masking and identification of ions.

Titrimetric methods of analysis. Titration methods: direct, reverse, displacement, indirect. Acid-base titration. Requirements for reactions in acid-base titration. Titration curves, equivalence point, end point of titration. Indicators. Primary and secondary standards, working solutions. Construction of titration curves, choice of indicator, titration error. Examples of practical applications of acid-base titration are the determination of HCl, NaOH, Na2CO3.

Complexometric titration. Requirements for complexation reactions used in titrimetry. Application of aminopolycarboxylic acids. Metallochromic indicators and requirements for them.

Construction of titration curves.

Colloquium No. 3.

Redox reactions.

Practical application in titrimetry. Instrumental methods of analysis.

Redox reactions. Reversible redox systems and their potentials. Equilibrium electrode potential. Nernst equation. Standard and formal redox potentials. The influence of various factors on the formal potential: pH of the solution, ionic strength of the solution, processes of complexation and precipitation, concentration of complexing substances and precipitants. Equilibrium constant of redox reactions and direction of oxidation-reduction reactions.

Redox titration. Construction of titration curves. Methods for fixing the titration end point in redox titrations. Methods: permanganatometric, iodometric, dichromatometric.

Spectroscopic methods of analysis. Basic characteristics of electromagnetic radiation (wavelength, frequency, wave number, intensity). Spectra of atoms. Methods of atomic emission and atomic absorption spectroscopy. Spectra of molecules. Bouguer-Lambert-Beer law.

Methods for determining the concentration of substances. Spectrophotometric and luminescent methods.

Electrochemical methods. Electrochemical cell, indicator electrode and reference electrode. Ionometry, potentiometric titration.

Coulometry: direct and coulometric titration; Faraday's law.

Classical voltammetry. Conductometry: direct and conductometric titration, in-line control capabilities.

Literature

1. Fundamentals of analytical chemistry. In 2 vols. P/ed. Yu.A. Zolotova. M.: Higher. school, 2000.

2. Fundamentals of analytical chemistry. Practical guide. P/ed. Yu.A. Zolotova.

M.: Higher. school, 2001.

3. Methods for detecting and separating elements. Practical guide.

P/ed. I.P. Alimarina. M.: MSU, 1984.

4. Belyavskaya T.A. Practical guide to gravimetry and titrimetry. M.:

5. Dorokhova E.N., Nikolaeva E.R., Shekhovtsova T.N. Analytical chemistry (methodological instructions). M.: MSU, 1988.

6. Reference book on analytical chemistry. P/ed. I.P. Alimarin and N.N. Ushakova. M.: MSU, 1975.

7. Ushakova N.N. Analytical chemistry course for soil scientists. M.: MSU, 1984.

8. Dorokhova E.N., Prokhorova G.V. Problems and questions in analytical chemistry. M.:

Mir, 1984 or M.: Academservice, 1997.

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1. Analytical reactions of group I cations.

Reactions of potassium ions.

1. Sodium hydrogen tartrate NaHC4H4O6. Add 3-4 drops of NaHC4H4O6 solution to 3-4 drops of K+ salt solution in a test tube. Mix the contents of the test tube with a glass rod; if a precipitate does not fall out immediately, lightly rub the walls of the test tube with the stick. The white crystalline precipitate of potassium hydrogen tartrate is soluble in hot water, strong acids, alkalis, and insoluble in acetic acid.

2. Sodium hexanitrocobaltate Na3. Add 1-2 drops of the reagent to a drop of K+ salt solution at pH 4-5 and, if a precipitate does not immediately form, allow the solution to stand or slightly heat it in a water bath. A bright yellow crystalline precipitate forms, soluble in strong acids but insoluble in acetic acid. Under the action of alkalis, the precipitate decomposes with the formation of a dark brown precipitate.

3. Microcrystalloscopic reaction with lead hexanitrocuprate Na2PbCu(NO2)6. A drop of K+ salt solution is placed on a glass slide, a drop of Na2PbCu(NO2)6 solution (the “K+ reagent”) is placed next to it, and the drops are connected with a glass rod. Allow to stand, after which the resulting cubic crystals are examined under a microscope.

4. Flame coloring. Volatile K+ salts (for example, KCl) turn the burner flame pale purple. In a direct vision spectroscope, a dark red line is observed at 769 nm. It is better to view the flame through blue glass or an indigo solution - under these conditions, potassium can be detected in the presence of sodium, because blue glass or indigo solution absorbs the yellow color of sodium.

Reactions of sodium ions.

1. Potassium antimonate K. Add 2-3 drops of Na+ salt solution to 2-3 drops of K solution and rub the walls of the test tube with a glass rod while cooling the test tube under running water. Leave the solution for a while and make sure that the precipitate is crystalline: closing the test tube with a rubber stopper, invert it. Large cubic crystals will be visible on the walls. The precipitate decomposes under the action of acids and dissolves in alkalis.

The reaction is insensitive.

2. Microcrystalloscopic reaction with zinc curanyl acetate Zn(UO2)3(CH3COO)8. A drop of Na+ salt solution is placed on a glass slide, a drop of Zn(UO2)3(CH3COO)8 solution is placed next to it, and the drops are connected with a glass rod. Allow to stand and examine the formed crystals under a microscope.

3. Flame coloring. Volatile Na+ salts (for example, NaCl) turn the burner flame yellow. In a direct vision spectroscope, a yellow line is observed at 590 nm.

Reactions of ammonium ions.

1. Strong alkalis. The reaction is carried out in a gas chamber. A glass cylinder is placed on a glass slide, inside which 1-2 drops of NH4+ salt solution and 1-2 drops of 2 M NaOH or KOH solution are added, making sure that the alkali solution does not get on the upper edge of the cylinder. Cover the cylinder with another glass slide, attaching to its inside wet indicator paper (universal indicator or litmus) or filter paper moistened with a Hg2(NO3)2 solution. Observe the color change of the indicator paper.

2. Nessler's reagent K2. Add 1-2 drops of Nessler's reagent to 1-2 drops of NH4+ salt solution in a test tube. An orange precipitate forms.

Reactions of magnesium ions.

1. Strong alkalis. To 2 drops of Mg2+ salt solution add 1-2 drops of NaOH solution. A white amorphous precipitate forms, soluble in acids and ammonium salts. The reaction can be used to separate Mg2+ from other group 1 cations, since their hydroxides are soluble in water.

2. Sodium hydrogen phosphate Na2HPO4. To 1-2 drops of Mg2+ salt solution in a test tube add 2-3 drops of 2 M HCl solution and 1-2 drops of Na2HPO4 solution. After this, a 2 M NH3 solution is added dropwise, stirring the contents of the test tube after each drop, until a distinct odor or a slightly alkaline reaction for phenolphthalein (pH ~ 9) is heard. A white crystalline precipitate forms, soluble in strong acids and acetic acid.

3. Quinalisarin. To 1-2 drops of Mg2+ salt solution add a drop of quinalizarin solution and 2 drops of 30% NaOH solution. A blue precipitate forms.

4. Microcrystalloscopic reaction. 1 drop of a Mg2+ salt solution is placed on a glass slide, and a drop of a reagent solution - a mixture of Na2HPO4, NH4Cl, NH3 - is placed next to it. A glass rod is used to connect the drops and examine the resulting crystals under a microscope.

2. Analytical reactions of group II cations.

Reactions of barium ions.

1. Potassium dichromate K2Cr2O7. To 1-2 drops of Ba2+ salt solution in a test tube add 3-4 drops of CH3COONa solution and 1-2 drops of K2Cr2O7 solution.

A yellow crystalline precipitate of BaCrO4 precipitates, insoluble in acetic acid, soluble in strong acids. The reaction is used to separate Ba2+ ions from other group II cations.

2. Sulfuric acid H2SO4. Add 2-3 drops of dilute sulfuric acid to 1-2 drops of Ba2+ salt solution. A white crystalline precipitate forms, insoluble in acids. To transfer BaSO4 into solution, it is transferred to BaCO3, carrying out repeated treatment of BaSO4 with a saturated solution of Na2CO3, each time draining the liquid from the precipitate, which is then dissolved in acid.

3. Flame coloring. Volatile Ba2+ salts color the burner flame yellow-green. In a direct vision spectroscope, a group of green lines is observed in the wavelength region 510-580 nm.

Reactions of calcium ions.

1. Ammonium oxalate (NH4)2C2O4. Add 2-3 drops of (NH4)2C2O4 solution to 2-3 drops of Ca2+ salt solution. A white crystalline precipitate forms, soluble in strong acids, but insoluble in acetic acid.

2. Microcrystalloscopic reaction. A drop of Ca2+ salt solution is placed on a glass slide, and a drop of H2SO4 solution (1:4) is placed next to it. The drops are connected with a glass rod, allowed to stand, and the resulting needle-shaped crystals are examined under a microscope (mainly at the edges of the drop).

3. Flame coloring. Volatile Ca2+ salts color the burner flame brick-red. In a direct vision spectroscope, a green line is observed at 554 nm and a red line at 622 nm. The lines are located symmetrically relative to the sodium line at 590 nm.

3. Analytical reactions of group III cations.

Reactions of lead ions.

1. Potassium dichromate K2Cr2O7. To 1-2 drops of Pb2+ salt solution in a test tube add 2-3 drops of 2 M CH3COOH solution, 2-3 drops of CH3COONa solution and 2 drops of K2Cr2O7 solution. A yellow precipitate of PbCrO4 precipitates. Centrifuge, separate the precipitate from the solution, and add 2-3 drops of 2 M NaOH solution to the precipitate.

The precipitate dissolves. This reaction makes it possible to distinguish PbCrO4 from BaCrO4, which is insoluble in NaOH.

2. Hydrochloric acid HCl. Add 3 drops of diluted HCl to 3-4 drops of Pb2+ salt solution in a test tube. A white precipitate forms, soluble in alkalis, as well as in excess HCl or alkali metal chlorides. PbCl2 is highly soluble in water, especially when heated, which is used when separating it from AgCl and Hg2Cl2.

3. Potassium iodide KI. Add 1-2 drops of KI solution to 1-2 drops of Pb2+ salt solution in a test tube. A yellow precipitate forms. A few drops of water and a 2 M CH3COOH solution are added to the test tube, heated, and the precipitate dissolves.

Immerse the test tube in cold water and observe the precipitation of golden crystals (“golden rain”).

4. Sulfuric acid H2SO4. To 2-3 drops of Pb2+ salt solution add 3-4 drops of diluted H2SO4, a white precipitate forms, soluble in solutions of strong alkalis or in concentrated solutions of CH3COONH4 or C4H4O6(NH4)2.

4. Analytical reactions of group IV cations.

Reactions of aluminum ions.

1. Alkalis or ammonia. To 3-4 drops of Al3+ salt solution, carefully add a 2 M alkali solution drop by drop until a white amorphous precipitate of aluminum hydroxide Al2O3.mH2O forms. When adding excess alkali, the precipitate dissolves. If solid NH4Cl is added and heated, a precipitate of aluminum hydroxide forms again.

2. Alizarin red. 1). Apply 1 drop of Al3+ salt solution to the filter, touching the paper with the tip of the capillary, 1 drop of alizarin red and treat the stain with ammonia gas, placing the paper over the opening of a bottle with a concentrated ammonia solution. A purple spot forms.

The purple color represents the color alizarin takes on in an alkaline environment. The paper is carefully dried, holding it high above the burner flame. In this case, the ammonia evaporates, and the violet color of alizarin turns into yellow, which does not interfere with the observation of the red color of the aluminum varnish.

The reaction is used for fractional detection of Al3+ in the presence of other cations. To do this, apply a drop of K4 solution to the filter paper and only then place a drop of Al3+ salt solution in the center of the wet spot. Cations that interfere with the reaction, for example, Fe3+, give poorly soluble hexacyanoferrates (II) and thus remain in the center of the spot. Al3+ ions, not precipitated by K4, diffuse to the periphery of the spot, where they can be detected by reaction with alizarin red in the presence of ammonia.

2). In a test tube, to 1-2 drops of Al3+ salt solution, add 2-3 drops of alizarin solution to NH3 solution until an alkaline reaction. The contents of the test tube are heated in a water bath. A red flocculent precipitate appears.

3. Aluminon. To 2 drops of Al3+ salt solution add 1-2 drops of aluminone solution and heat in a water bath. Then add a solution of NH3 (until the smell appears) and 2-3 drops of (NH4)2CO3. Red flakes of aluminum varnish are formed.

Reactions of chromium(III) ions.

1. Caustic alkalis. Add 2-3 drops of 2 M NaOH solution to 2-3 drops of Cr3+ salt solution. A gray-green precipitate forms. The precipitate is soluble in acids and alkalis.

2. Hydrogen peroxide H2O2. To 2-3 drops of a Cr3+ salt solution, add 4-5 drops of a 2 M NaOH solution, 2-3 drops of a 3% H2O2 solution and heat for several minutes until the green color of the solution turns yellow.

The solution is saved for further experiments (detection of CrO42-).

3. Ammonium persulfate (NH4)2S2O8. To 5-6 drops of (NH4)2S2O8 solution add 1 drop of 1 M solution of H2SO4 and AgNO3 (catalyst). 2-3 drops of a solution of Cr2(SO4)3 or Cr(NO3)3 are added to the resulting oxidizing mixture and heated. The solution turns yellow-orange. It is saved for further experiments (Cr2O72-).

4. Sodium ethylenediaminetetraacetate (EDTA). To 3-4 drops of a Cr3+ salt solution, add 3-5 drops of a 30% CH3COOH solution, 12-15 drops of an EDTA solution (excess EDTA is required), check the pH of the solution (pH 4-5) and heat in a water bath. In the presence of Cr3+, a violet color appears.

Reactions of Cr(VI) ions.

1. Formation of perchromic acid H2CrO6. 5-6 drops of the chromate solution obtained earlier are placed in a test tube. Excess H2O2 is removed by boiling in a water bath, and the test tube is cooled under running tap water. A few drops of ether, 1 drop of a 3% solution of H2O2 and drop by drop with shaking H2SO4 (1:4) are added to the solution. The resulting chromium peroxide compound is extracted with ether, and the ether layer turns blue.

Reactions of zinc ions.

1. Caustic alkalis. Add 2-3 drops of a 2 M NaOH solution to 2-3 drops of a Zn2+ salt solution, a white precipitate forms, soluble in acids, alkalis and ammonium salts (different from aluminum hydroxide).

2. Ammonium tetrarodanomercurate (NH4)2 forms a white crystalline precipitate of Zn with solutions of Zn2+ salts. Typically the reaction is carried out in the presence of a small amount of Co2+ salt. The role of Zn2+ is that the Zn precipitate it forms accelerates, like a seed, the precipitation of a blue Co precipitate, which in the absence of Zn may not precipitate for hours (formation of a supersaturated solution).

In a test tube, add 1-2 drops of water and 3-4 drops of (NH4)2 to 1-2 drops of Co2+ salt. The walls of the test tube are rubbed with a glass rod, and no blue precipitate should appear. Then add a drop of Zn2+ salt solution to the same test tube and rub the walls again with a glass rod. In this case, mixed crystals of both compounds are formed, colored pale blue or dark blue, depending on the amount of Co2+.

3. Hydrogen sulfide and soluble sulfides. To 1-2 drops of Zn2+ salt solution add 1-2 drops of hydrogen sulfide water (or a drop of Na2S). A white precipitate forms, soluble in strong acids.

4. Microcrystalloscopic reaction. A drop of Zn2+ salt solution is placed on a glass slide, a drop of the reagent (NH4)2 is placed next to it, and the drops are connected with a glass rod. Characteristic dendrites are examined under a microscope.

5. Reactions of group V cations.

Reactions of iron(II) ions.

1. Potassium hexacyanoferrate(III) K3. To 1-2 drops of Fe2+ salt solution add 1-2 drops of reagent solution. A dark blue precipitate (“Prussian blue”) forms.

Reactions of iron(III) ions.

1. Potassium hexacyanoferrate(II) K4. Add 1-2 drops of the reagent to 1-2 drops of Fe3+ salt solution. The formation of a dark blue Prussian blue precipitate is observed.

2. Ammonium (potassium) thiocyanate NH4SCN. To 1-2 drops of Fe3+ salt solution add a few drops of NH4SCN (or KSCN) solution. A dark red color appears.

Reactions of manganese ions.

1. Action of strong oxidizing agents.

A). Lead(IV) oxide PbO2. A little PbO2 powder, 4-5 drops of a 6 M HNO3 solution, a drop of Mn2+ salt solution are placed in a test tube and heated. After 1-2 minutes, centrifuge and, without separating the precipitate, examine the color of the solution. The solution turns crimson-violet.

b). Ammonium persulfate (NH4)2S2O8. To 5-6 drops of (NH4)2S2O8 solution add a drop of 2 M H2SO4 solution, 1-2 drops of concentrated H3PO4 (to prevent the decomposition of permanganate ions), 1-2 drops of AgNO3 solution (catalyst) and heat. Using a glass spatula, add a minimum amount of Mn2+ salt solution to the heated oxidizing mixture, mix and observe the crimson-violet color of the solution.

V). Sodium bismuthate NaBiO3. To 1-2 drops of Mn2+ salt solution add 3-4 drops of 6 M HNO3 solution and 5-6 drops of water, after which a little NaBiO3 powder is added to the solution with a glass spatula. After mixing, centrifuge the excess reagent and observe the crimson color of the solution.

2. Pyridylazonaphthol (PAN). To 2-3 drops of Mn2+ salt solution add 5-7 drops of water, 4-5 drops of 0.1% ethanol solution of PAN, NH3 to pH 10 and extract with chloroform. The organic phase turns red.

6. Reactions of group VI cations.

Reactions of cobalt ions.

1. Ammonium (potassium) thiocyanate NH4SCN. To 2-3 drops of Co2+ salt solution add solid NH4SCN (KSCN), solid NH4F to bind Fe3+ into a stable colorless complex, 5-7 drops of isoamyl alcohol and shake.

The isoamyl alcohol layer turns blue.

2. Ammonia NH3. To 1-2 drops of Co2+ salt solution add 3-4 drops of NH3 solution. A blue precipitate of the main cobalt salt precipitates, which, with a large excess of NH3, dissolves to form a complex compound of a dirty yellow color.

3. Sodium hydroxide NaOH. Add 2-3 drops of a 2 M large NaOH solution to 2-3 drops of a Co2+ salt solution, and a blue precipitate forms. The precipitate dissolves in mineral acids.

4. Microcrystalloscopic reaction. A drop of Co2+ salt solution is placed on a glass slide, a drop of reagent solution (NH4)2 is placed next to it, the drops are connected with a glass rod, and the resulting bright blue crystals are examined under a microscope.

Reactions of nickel ions.

1. Dimethylglyoxime. In a test tube, add 1-2 drops of dimethylglyoxime solution and 1-2 drops of 2 M NH3 to 1-2 drops of Ni2+ salt solution. A characteristic scarlet-red precipitate forms.

2. Ammonia NH3. To 1-2 drops of Ni2+ salt solution in a test tube, add NH3 solution drop by drop until a blue solution is formed.

3. Sodium hydroxide NaOH. Add 2-3 drops of 2 M NaOH solution to 2-3 drops of Ni2+ salt solution, a green precipitate is formed, soluble in acids.

Reactions of copper ions.

1. Ammonia NH3. Add NH3 solution drop by drop to 1-2 drops of Cu2+ salt solution. A green precipitate of the basic salt of variable composition precipitates, easily soluble in excess NH3 to form a blue complex compound.

2. Potassium hexacyanoferrate(II) K4. To 1-2 drops of Cu2+ salt solution (pH

7) add 1-2 drops of K4 solution. A red-brown precipitate forms.

3. Potassium iodide KI. To 2-3 drops of Cu2+ salt solution add 1 drop of 1 M H2SO4 solution and 5-6 drops of 5% KI solution, a white precipitate forms.

Due to the release of iodine, the suspension has a yellow color.

Reactions of cadmium ions.

1. Hydrogen sulfide or sodium sulfide Na2S. Add 1 drop of Na2S solution to 1-2 drops of Cd2+ salt solution, and a yellow precipitate forms.

2. Diphenylcarbazide. Apply 1 drop of a saturated diphenylcarbazide solution and a drop of Cd2+ salt solution to the filter paper and hold it for 2-3 minutes over a concentrated NH3 solution. A blue-violet color appears. In the presence of interfering ions, solid KSCN and KI are first added to the ethanol solution of diphenylcarbazide.

7. Reactions of anions Reactions of sulfate ions.

1. Barium chloride BaCl2. To 1-2 drops of SO42- solution add 2-3 drops of BaCl2 solution. A white crystalline precipitate forms, insoluble in acids. This distinguishes the BaSO4 precipitate from Ba2+ salts with all other anions, which is what is used when detecting SO42-.

Reactions of carbonate ions.

1. Acids. The reactions are carried out in a gas detection device. A little carbonate (dry preparation) or 5-6 drops of a CaCO3 solution are placed in a test tube, and 5-6 drops of a 2 M HCl solution are added. Close with a stopper with a gas outlet tube, the second end of which is lowered into a test tube with lime water [saturated solution of Ca(OH)2] and observe the turbidity of the lime water.

Reactions of chloride ions.

1. Silver nitrate AgNO3. To 2-3 drops of Cl- solution add 2-3 drops of AgNO3 solution. A white cheesy precipitate forms. AgCl is insoluble in HNO3; easily dissolves under the influence of substances capable of binding Ag+ into a complex, for example, NH3; (NH4)2CO3 (difference from AgBr, AgI); KCN, Na2S2O3.

Reactions of nitrate ions.

1. Iron(II) sulfate FeSO4. A small FeSO4 crystal is added to a drop of the NO3- solution under study, placed on a drop plate or on a watch glass, a drop of a concentrated H2SO4 solution is added, and a brown ring appears around the crystal.

2. Aluminum or zinc. Add 3-4 drops of 2 M NaOH solution to a test tube with 3-4 drops of NO3- solution and add 1-2 pieces of aluminum or zinc metal. The test tube is closed loosely with cotton wool, on top of which damp red litmus paper is placed and heated in a water bath. Litmus paper turns blue.

3. Diphenylamine (C6H5)2NH. Place 2-3 drops of a solution of diphenylamine in concentrated H2SO4 on a thoroughly washed and dry watch glass or in a porcelain cup. (If the solution turns blue, the glass or cup was not clean enough). Add a very small amount of the NO3- solution to be tested at the tip of a clean glass rod and mix. An intense blue color appears.

Reactions of phosphate ions.

1. Molybdenum liquid (solution of (NH4)2MoO4 in HNO3). To 1-2 drops of PO43- solution add 8-10 drops of molybdenum liquid and slightly heat to 40°C. A yellow crystalline precipitate forms, insoluble in HNO3, easily soluble in caustic alkalis and NH3.

III. QUANTITATIVE ANALYSIS

Determination of the quantity of a substance is based on a physical measurement of some physical or chemical property of that substance, which is a function of its mass or concentration. There are many quantitative analysis methods.

They can be divided into two groups:

1) methods based on direct measurement of the mass of the substance being determined, that is, based on direct weighing on scales;

2) indirect methods for determining mass, based on the measurement of certain properties associated with the mass of the component being determined.

Depending on the measured properties, quantitative analysis methods are divided into chemical, physicochemical and physical. Chemical methods include gravimetry and titrimetry with visual indication of the titration end point.

1. Gravimetric methods Gravimetry is the simplest and most accurate, although rather time-consuming method of analysis. The essence of gravimetry is that the determined component of the analyzed substance is isolated either in pure form or in the form of a compound of a certain composition, which is then weighed. Gravimetric methods are divided into distillation methods and precipitation methods. Precipitation methods are of greatest importance. In these methods, the component being determined is precipitated in the form of a poorly soluble compound, which, after appropriate treatment (separation from the solution, washing, drying or calcination), is weighed. When precipitating, you always need to take some excess of the precipitant. To obtain clean, uniform in dispersion, possibly coarse-crystalline sediments (if the substance is crystalline), or well-coagulated sediments (if the substance is amorphous), a number of rules must be followed. The composition of the substance to be weighed (gravimetric form) must strictly correspond to a certain chemical formula.

Gravimetric determination of sulfuric acid in solution Determination of sulfuric acid or sulfate is based on the formation of a crystalline precipitate of BaSO4 by the reaction:

SO42- + Ba2+ = BaSO4 The precipitated form is BaSO4. The precipitate is isolated from a heated weakly acidic solution.

The precipitate is calcined at a temperature of about 800oC (gas burner).

Gravimetric form - BaSO4.

Reagents Hydrochloric acid, HCl, 2 M solution.

Barium chloride, BaCl2. 2H2O, 5% solution.

Silver nitrate, AgNO3, 1% solution.

Nitric acid, HNO3, 2 M solution.

Execution of definition. H2SO4 solution received from the teacher in a glass. 300 ml, previously washed until completely drainable, is diluted with distilled water to 100-150 ml, 2-3 ml of 2 M HCl is added to the solution, the solution is heated almost to a boil and the calculated volume of barium chloride solution is poured into it dropwise from a burette. The amount of precipitant is calculated taking into account a 10% excess. While adding the precipitant, the solution is stirred with a glass rod. Allow the precipitate to collect at the bottom of the glass and check the completeness of precipitation by adding a few drops of precipitant.

If complete precipitation is not achieved, add a few more milliliters of barium chloride solution. Remove the stick from the glass, cover the glass with a watch glass (or a clean sheet of paper) and leave to stand for at least 12 hours.

The maturation of the sediment can be accelerated if, before precipitation, 2 - 3 ml of a 1% solution of picric acid is added to the test solution. In this case, it is enough to leave the solution with the precipitate for 1 - 2 hours in a warm place (for example, in a water bath) before filtering.

The precipitate is filtered on a blue ribbon filter, first pouring the clear liquid onto the filter and collecting the filtrate in a clean glass. It is useful to check the first portions of the filtrate for completeness of sedimentation. When most of the clear liquid passes through the filter, and almost all of the sediment remains in the glass where the precipitation was carried out, pour out the filtrate and place an empty glass under the funnel. Then the sediment is transferred to the filter with small portions of cold distilled water from the washing machine. Particles of sediment adhering to the walls of the glass are removed with a stick with a rubber tip. The glass rod is thoroughly wiped with a piece of wet filter, and then this piece of filter is placed in the funnel. You can wipe the inside of the glass with a piece of damp filter. When all the sediment has been transferred to the filter, it is washed on the filter 3-4 times with cold water in portions of 10-15 ml. The last washing waters are checked for completeness of washing with a solution of AgNO3 in a 2 M HNO3 medium (only weak opalescence is acceptable). Then the funnel with the filter is placed in a drying cabinet for several minutes, the filter with the sediment is dried and, bending the edges of the filter towards the center, the slightly damp filter with the sediment is placed in a porcelain crucible brought to a constant mass (a clean, empty crucible is heated over a full flame of a gas burner). Insert the crucible into the triangle and, holding it high above the small flame of the burner, dry the filter and char it.

When charring is complete, increase the burner flame, lower the triangle with the crucible, allow the coal to burn out, and then calcinate the sediment over a full burner flame for 10 - 15 minutes. After cooling in the desiccator, the crucible with the sediment is weighed.

Repeat 10-minute calcinations until constant weight is achieved (±0.2 mg).

Calculate the H2SO4 content in the solution:

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In titrimetric analysis, the amount of chemical substances is most often determined by accurately measuring the volumes of solutions of two substances that react with each other. Unlike gravimetry, the reagent is taken in an amount equivalent to the substance being determined. Methods of titrimetric analysis can be classified according to the nature of the chemical reaction underlying the determination of substances. These reactions belong to different types - ion combination reactions and oxidation-reduction reactions. In accordance with this, titrimetric determinations are divided into the following main methods: acid-base titration method, complexometric and precipitation titration methods, redox titration methods.

Some general instructions for work

1. After the burettes or pipettes have been thoroughly washed, before filling they should be rinsed (2-3 times 5 ml each) with the solution with which they will be filled.

2. Each solution should be titrated at least three times. The spread of the results of three titrations should not exceed 0.1 ml.

3. When determining the volume of a burette drop, fill it to zero with distilled water, release 100 drops (drops should drip evenly at a speed of 2 - 3 per second) and note the volume on the burette (the count is carried out no earlier than 30 s after pouring out the water). The resulting volume is divided by 100. The determination is repeated at least three times, each time calculating the volume of the drop to 0.001 ml. The differences between the three determinations should not exceed 0.01 ml.

Calculations in titrimetric analysis Substances react with each other in equivalent quantities (n1 = n2).

Equivalent - a conditional or real particle that can add, release, replace one proton in acid-base reactions or be equivalent to one electron in redox reactions.

If analyte A reacts with titrant B according to the equation:

aA + bB = cC + dD, then from this equation it follows that one particle A is equivalent to b/a particles of substance B. The ratio b/a is called the equivalence factor and is denoted feq.

For example, for the acid-base reaction H3PO4 + NaOH = NaH2PO4 feq(H3PO4) = 1, and for the reaction:

H3PO4 + 2 NaOH = Na2HPO4 + 2 H2O feq(H3PO4) = 1/2.

In the redox half-reaction:

MnO4- + 8 H+ + 5 e = Mn2+ + 5 H2O feq(KMnO4) = 1/5, but in the half-reaction:

MnO4- + 4 H+ + 3 e = MnO(OH)2 + H2O feq(KMnO4) = 1/3.

The molecular weight of the equivalent of a substance is the mass of one mole equivalent of this substance, which is equal to the product of the equivalence factor and the molecular weight of the substance.

Since the number of equivalents of substances entering the reaction is n = cVx10-3, where c is the molar concentration and V is the volume, then for two stoichiometrically reacting substances the equality holds:

If the molar concentration of one substance is known, then by measuring the volumes of the reacting substances, the unknown concentration of the second substance can be calculated.

Molar concentration c is the ratio of the number of moles of solute to volume. For example, c(1/2 H2SO4) = 0.1 mol/l or c(1/2 H2SO4) = 0.1 M; this means that 1 liter of solution contains 6.02.10-23x0.1 conventional particles of 1/2 H2SO4 or 4.9 g of H2SO4 is dissolved in 1 liter.

For example, a Ba(OH)2 solution was standardized to a 0.1280 M HCl solution. To titrate 46.25 ml of acid solution, 31.76 ml of base solution was required.

Therefore, c(1/2 Ba(OH)2) = (46.25 x 0.1280)/31.76 = 0.1864 M and m = c x M x f eq = 0.1864 x 171.34 x 1 /2 = 15.97 g/l.

In complexation reactions, it is quite difficult to define the concept of “molecular mass equivalent” for a substance. In this case, the stoichiometry of the reaction is usually taken into account. For example, in complexometry, regardless of the charge of the cation, reactions proceed according to the equation Mn2+ + H2Y2- = MY(n - 4)+ + 2 H+, that is, with the formation of complexes of composition 1:1. Therefore, for the components involved in this reaction, the molecular weights of the equivalents are equal to the molecular weights.

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Preparation of the primary standard (Na2СО3) and working solutions (0.1 M HCl and 0.1 M NaOH) Calculate a sample of Na2СО3 with an accuracy of 0.0001 g to prepare 250 ml of a 0.1000 M solution. On a technical scale, a quantity of Na2CO3 close to the calculated amount is weighed in a weighing cup and the mass of the weighed cup is determined on an analytical balance. Transfer Na2CO3 through a dry funnel into a volumetric flask. 250 ml, and the glass is weighed on an analytical balance and the sample is found by difference. The funnel is washed with distilled water, the soda is dissolved in a small amount of distilled water, then the solution is brought to the mark and mixed thoroughly. Working solutions - 0.1 M HCl and 0.1 M NaOH - are prepared in bottles containing 2 liters of distilled water, adding the calculated amounts of concentrated HCl (pl. 1.19) and 2 M NaOH solution using a graduated cylinder, respectively. The solutions are thoroughly mixed, the bottles are closed with siphons and the label is glued. In the case of NaOH solution, the siphon is closed with a calcium chloride tube.

Standardization of hydrochloric acid by sodium carbonate The CO32- ion is a base capable of sequentially adding protons:

CO32- + H+ = HCO3HCO3- + H+ = H2CO3 You can titrate with an acid either until the formation of HCO3- (NaHCO3) in the solution, or to H2CO3. In the first case, half of the sodium carbonate is titrated, in the second

All sodium carbonate. Naturally, if the titration is to NaHCO3 (the pH of this solution is 8.34, so the titration is carried out in the presence of phenolphthalein as an indicator), then to calculate the amount of Na2CO3 in the solution under study, you need to double the number of milliliters of hydrochloric acid used for titration.

If titrated to H2CO3 (pH of the solution is 4.25), then using methyl orange as an indicator, titrate all the sodium carbonate. Reagents: Hydrochloric acid, HCl, 0.1 M solution.

Sodium carbonate, Na2CO3, 0.1 M (1/2 Na2CO3) solution.

Methyl orange indicator, 0.1% aqueous solution.

Execution of definition. A solution of hydrochloric acid is poured into the burette.

Pipette 10 ml of sodium carbonate solution and transfer it to a conical titration flask. 100 ml, add 20 ml of distilled water and 1 drop of methyl orange and titrate with hydrochloric acid until the color of the solution changes from yellow to orange.

When titrating with methyl orange, it is convenient to use a witness, that is, a solution that has a color to which the test solution should be titrated. To prepare the witness, add 40 ml of distilled water, one drop of methyl orange and 1 - 2 drops of 0.1 M acid solution into a 100 ml conical titration flask using a graduated cylinder until an orange color appears.

Standardization of sodium hydroxide solution against hydrochloric acid Due to the large pH jump in the titration curve and the fact that the equivalence point corresponds to pH 7, strong acids can be titrated with strong bases with indicators whose pT values lie at both pH 7 and pH 7.

Reagents Hydrochloric acid, HCl, 0.1 M solution.

Sodium hydroxide, NaOH, 0.1 M solution.

Execution of definition. 1. Titration with methyl orange. A sodium hydroxide solution is poured into a burette that has been thoroughly washed and then rinsed with sodium hydroxide solution and the burette is closed with a calcium chloride tube. After rinsing the pipette with a solution of hydrochloric acid, take 10 ml of this solution with a pipette and transfer it to a conical titration flask with a capacity of 100 ml, add 20 ml of distilled water, 1 drop of methyl orange with a graduated cylinder and titrate with a solution of sodium hydroxide until the color of the solution changes from red to orange to pure yellow. Titrate at least three times. The results of three titrations should differ from each other by no more than 0.1 ml.

2. Titration with phenolphthalein. Pipette 10 ml of hydrochloric acid solution and 2-3 drops of phenolphthalein into a titration flask and titrate with sodium hydroxide solution until a pale pink color is stable for 30 s. It is necessary to titrate as quickly as possible; the solution should not be stirred too vigorously to avoid the solution absorbing CO2 from the air.

Determination of hydrochloric acid Reagents Sodium hydroxide, NaOH, 0.1 M solution.

Indicators: methyl orange, 0.1% aqueous solution; or phenolphthalein, 0.1% solution in 60% ethanol.

Execution of definition. The solution received from the teacher in a volumetric flask is brought to the mark with distilled water, mixed thoroughly, an aliquot (10 ml) is pipetted and transferred to a conical flask for titration. Add 1-2 drops of indicator and titrate with NaOH solution from a burette covered with a calcium chloride tube. until the color of the indicator changes (see "Standardization of sodium hydroxide with hydrochloric acid").

Calculate the HCl content in the solution using the formula:

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Complexometric titration is based on the formation reactions of metal ions with aminopolycarboxylic acids (complexones). Of the numerous aminopolycarboxylic acids, the most commonly used is ethylenediaminetetraacetic acid (H4Y) HOOC H2C CH2 COOH N CH2 CH2 N HOOC H2C CH2 COOH Due to its low solubility in water, the acid itself is not suitable for preparing a titrant solution. For this purpose, the dihydrate of its disodium salt Na2H2Y.2H2O (EDTA) is usually used. This salt can be prepared by adding sodium hydroxide to an acid suspension until the pH is ~5. In most cases, a commercial preparation is used to prepare an EDTA solution, and then the solution is standardized. You can also use EDTA fixanal.

The interaction reactions of cations with different charges with EDTA in solution can be represented by the equations:

Ca2+ + H2Y2- = CaY2- + 2 H+ Bi3+ + H2Y2- = BiY- + 2 H+ Th4+ + H2Y2- = ThY + 2 H+ It can be seen that, regardless of the charge of the cation, complexes are formed with a component ratio of 1:1. Therefore, the molecular weights of the EDTA equivalent and the metal ion being determined are equal to their molecular weights. The extent of the reaction depends on the pH and stability constant of the complexonate.

Cations that form stable complexonates, for example, Fe(III), can be titrated in acidic solutions. Ca2+, Mg2+ and other ions, which form relatively less stable complexonates, are titrated at pH 9 and higher.

The end point of titration is determined using metal indicators of chromophore organic substances that form intensely colored complexes with metal ions.

Determination of calcium and magnesium in the joint presence The stability constants of calcium and magnesium complexonates differ by 2 orders of magnitude (the logarithms of the stability constants are 10.7 and 8.7 for calcium and magnesium, respectively, at 20 ° C and an ionic strength of 0.1). Therefore, these ions cannot be titrated separately using only the difference in the stability constants of the complexonates. At pHopt ~ 9 - 10, eriochrome black T is used as a metal indicator. Under these conditions, the amount of calcium and magnesium is determined.

In another aliquot, pH 12 is created by introducing NaOH, while magnesium is precipitated in the form of hydroxide, it is not filtered, and calcium in the solution is determined complexometrically in the presence of murexide, fluorexone or calcium, which are metal indicators for calcium. Magnesium is determined by the difference.

The method is suitable for determining water hardness. Traces of heavy metals are titrated together with calcium and magnesium; therefore, they are masked before titration with potassium cyanide or precipitated with sodium sulfide or sodium diethyldithiocarbamate. Almost all ions present in water can be masked with potassium cyanide and triethanolamine; Alkali metals, calcium and magnesium are not masked.

1.0 ml of 0.0100 M EDTA solution is equivalent to the content of 0.408 mg Ca;

0.561 mg CaO; 0.243 mg Mg; 0.403 mg MgO.

Reagents EDTA, 0.05 M solution.

Ammonia buffer solution with pH 10 (67 g NH4Cl and 570 ml of 25% NH3 in 1 liter of solution).

NaOH or KOH, 2 M solutions.

Metal indicators: eriochrome black T; murexide (fluorexone or calcion can be used instead of murexide), (mixtures with sodium chloride in a ratio of 1:100).

Carrying out the definition.1. Determination of the amount of calcium and magnesium.

Pipette 10 ml of the analyzed solution from a 100 ml volumetric flask into a 100 ml conical titration flask, add 2 - 3 ml of a buffer solution with pH 10, 15 ml of water, mix and add 20 on the tip of a spatula

30 mg mixture of eriochrome black T and sodium chloride. Stir until the indicator mixture is completely dissolved and titrate with EDTA solution until the color of the solution changes from wine red to blue.

2. Determination of calcium. Pipette 10 ml of the analyzed solution into a 100 ml conical flask, add 2 - 3 ml of NaOH or KOH solutions, dilute with water to approximately 25 ml, add 20 - 30 mg of indicator mixtures of murexide, fluorexone or calcium with sodium chloride and titrate with EDTA solution until the color of the solution changes from one drop of EDTA solution.

The color change at the end point of the titration depends on the metal indicator chosen. When murexide is used, the color changes from pink to lilac-violet; when using fluorexone - from yellow with green fluorescence to colorless or pinkish with a sharp decrease in fluorescence intensity; when using calcium - from pale yellow to orange. In the latter case, an alkaline environment is created only with a 2 M KOH solution.

3. Determination of magnesium. The volume of titrant used for the titration of magnesium is calculated from the difference in the volumes of EDTA used for titration at pH 10 and at pH 12.

a cV MV m= CaO EDTA EDTA k

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2.3. Redox titration The methods used are based on oxidation-reduction reactions. They are usually named according to the titrant used, for example, dichromatometry, iodometry, permanganatometry, bromatometry. In these methods, K2Cr2O7, I2, KMnO4, KBrO3, etc. are used as titrated solutions, respectively.

2.3.1. Dichromatometry

In dichromatometry, the primary standard is potassium dichromate. It can be prepared by precise weighing, since it is easily purified by recrystallization from an aqueous solution and maintains a constant concentration for a long time.

In an acidic environment, dichromate is a strong oxidizing agent and is used to determine reducing agents; it itself is reduced to chromium(III):

Cr2O72- + 14 H+ + 6e = 2 Cr3+ + 7 H2O Еo(Cr2O72-/2 Cr3+) = 1.33 V When titrating with potassium dichromate, redox indicators are used - diphenylamine, diphenylbenzidine, etc.

Determination of iron(II)

Titration of iron(II) is based on the reaction:

6 Fe2+ + Cr2O72- + 14 H+ = 6 Fe3+ + 2 Cr3+ + 7 H2O During the titration process, the concentration of iron(III) ions increases and the potential of the Fe3+/Fe2+ system increases, which leads to premature oxidation of the diphenylamine indicator. If phosphoric acid is added to the titrated solution, the color of the indicator changes sharply at the end point of the titration.

Phosphoric acid lowers the redox potential of the Fe3+/Fe2+ system, forming a stable complex with iron(III) ions.

Solutions of iron(II) salts often contain iron(III) ions, so iron(III) ions must be reduced before titration. Metals (zinc, cadmium, etc.), SnCl2, H2S, SO2 and other reducing agents are used for reduction.

Reagents Potassium dichromate, K2Cr2O7, 0.05 M (1/6 K2Cr2O7) solution.

Hydrochloric acid, HCl, concentrated, pl. 1.17.

Sulfuric acid, H2SO4, concentrated, pl. 1.84.

Phosphoric acid, H3PO4, concentrated with pl. 1.7.

Zinc metal, granular.

Diphenylamine indicator, 1% solution in concentrated H2SO4.

Execution of definition. A 10 ml aliquot of the solution is pipetted into a conical titration flask. 100 ml, add 5 ml conc.

HCl. Close the flask with a small funnel, add 3-4 granules of metallic zinc and heat in a sand bath (the reaction should not be very violent) until the solution becomes discolored and the zinc is completely dissolved. Cool under running cold water, add 3 - 4 ml of H2SO4, cool, add 5 ml of H3PO4, 15

20 ml of distilled water, 2 drops of diphenylamine solution and titrate with potassium dichromate solution until a blue color appears.

Find content using the formula:

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In a strongly acidic environment, permanganate ions have a high redox potential, being reduced to Mn2+, and they are used to determine many reducing agents:

MnO4- + 5 e + 8 H+ = Mn2+ + 4 H2O Eo(MnO4-/Mn2+) = 1.51 V.

When titrating with permanganate, as a rule, indicators are not used, since the reagent itself is colored and is a sensitive indicator: 0.1 ml of a 0.01 M KMnO4 solution turns 100 ml of water pale pink.

A standard solution of Na2C2O4 is prepared either by weighing (accuracy up to 0.0001 g) or from fixanal. The working solution of KMnO4 is prepared in a bottle containing 2 liters of distilled water by diluting the calculated amount of 1 M solution;

the resulting solution is thoroughly mixed and closed with a siphon with a calcium chloride tube.

Standardization of a solution of potassium permanganate by sodium oxalate The reaction between oxalate ions and permanganate ions is complex and is not described by the often given equation:

5 C2O42- + 2 MnO4- + 16 H+ = 2 Mn2+ + 8 H2O + 10 CO2, although the starting and final products correspond to those given in the written equation. In reality, the reaction occurs in several stages, and for it to begin, at least traces of Mn2+ must be present in the solution:

MnO4- + MnC2O4 = MnO42- + MnC2O4+

Manganate ion in an acidic solution quickly disproportionates:

Mn(VI) + Mn(II) = 2 Mn(IV) Mn(IV) + Mn(II) = 2 Mn(III) Manganese(III) forms oxalate complexes of the composition Mn(C2O4)n(3-2n)+, where n = 1, 2, 3; they slowly decompose to form Mn(II) and CO2. Thus, until sufficient concentrations of manganese(II) accumulate in the solution, the reaction between MnO4- and C2O42- proceeds very slowly. When the concentration of manganese(II) reaches a certain value, the reaction begins to proceed at high speed.

Sulfuric acid, H2SO4, 2 M solution.

Execution of definition. Pour 20 ml of H2SO4 into a 100 ml titration flask and heat it to 80 - 90oC. 10 ml of sodium oxalate solution is pipetted into the hot solution and titrated with a permanganate solution, and at the beginning of the titration, the next drop of KMnO4 solution is added only after the color from the previous drop has completely disappeared. Then, increasing the titration speed, titrate until a pale pink color appears, which is stable for 30 s.

Permanganatometric determination of the oxidability of water (or water extract from soil) The oxidability of water or soil is due to the presence of water-soluble organic substances capable of oxidation. The oxidability of water or aqueous extract from soils is determined by indirect redox titration, for which the excess of the oxidizing agent that has not reacted with organic substances is titrated. Thus, organic substances are oxidized with permanganate in an acidic environment, excess permanganate is reacted with sodium oxalate, and its excess is titrated with potassium permanganate. Significant release of manganese(IV) oxide prevents direct titration of excess permanganate with an accurate volume of sodium oxalate.

Reagents Potassium permanganate, KMnO4, 0.05 M (1/5 KMnO4) solution.

Sodium oxalate, Na2C2O4, 0.05 M (1/2 Na2C2O4) solution.

Sulfuric acid, H2SO4, 1 M solution.

Execution of definition. An aliquot of the analyzed solution (10 ml) is transferred to a conical titration flask, 20 ml of sulfuric acid is added, heated to 70-80°C and 10 ml of a standard KMnO4 solution is introduced from a burette. The solution should remain colored. If the solution becomes discolored, another 5 ml of KMnO4 solution should be added. Into a heated solution

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where c1 is the concentration of a solution of 1/5 KMnO4, M c2 is the concentration of a solution of 1/2 Na2C2O4, M V1 is the volume of the KMnO4 solution added to the aliquot, ml, V2 is the volume of the KMnO4 solution used for titrating the excess Na2C2O4, ml, V3 - volume of added standard Na2C2O4 solution, ml.

Sometimes oxidability is expressed in carbon units: 3n(mol)/1000 (g).

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