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Flame coloring as one of the methods of analytical chemistry. Metals of the main subgroups Sodium ions color the flame

♣ Flame coloring with metal salts

Salts of some metal elements (* which ones?) when introduced into the flame, they color it. This property can be used in qualitative analysis to detect cations of these elements in the sample being studied.

To carry out the experiment, a nichrome wire is required. It should be washed with conc. HCl and ignite in a burner flame. If the flame is colored when adding the wire, repeat the HCl treatment.

Immerse the wire in the solution of the salt being tested and bring it into the flame. Note coloring. After each experiment, rinse and ignite the wire until the color of the flame disappears.

Experiments on the topic “Metals of groups I and II”

1. Flame coloring

Conduct an experiment on coloring the flame with chlorides of alkali and alkaline earth metals. * Why do they take chlorides and not other salts?

Flame coloring with salts (from left to right): lithium, sodium, potassium, rubidium, cesium, calcium, strontium, barium.

(photo of potassium flame - V.V. Zagorsky)

2. Combustion of magnesium in air

Take a piece of magnesium strip with crucible tongs and burn it over a porcelain cup. Prove what the product is. * How to do it?

3. Interaction of magnesium with water and acids

A) Pour some water into the test tube, add phenolphthalein and add a little magnesium powder. If necessary, heat the test tube. * Remember how calcium interacts with water.

B) Pour 1 ml of conc. into one test tube. HCl, and in the second - 1 ml of conc. HNO3. Place a piece of magnesium tape in each test tube. * What products are formed? How can this be proven?

Experiments on the topic “Aluminium”

1. Interaction of aluminum with acids and alkalis

Study the interaction of aluminum granules with solutions in test tubes:

in the cold

when heated

conc. H2SO4

Observations are presented in the form of a table.

* Remember how aluminum reacts withNaOH.

2. Aluminum hydroxide

Prepare aluminum hydroxide in three test tubes by dropping 1 M ammonia solution to 1 ml of aluminum salt solution. Treat the hydroxide in the first test tube with an excess of ammonia solution, in the second with an HCl solution, and in the third with a NaOH solution. In the solution obtained in the third test tube (* what is this solution?), skip CO 2. * How and in what device to get it?


3. Hydrolysis of aluminum salts

A) Determine the pH of the aluminum chloride solution. * Explain the result using the constant of the corresponding process.

B) Add 1 M sodium carbonate solution to the aluminum chloride solution.

4. Aluminothermy(one of the experiments, to choose from, is carried out under traction, in the presence of a teacher)

A) Aluminothermic production of chromium

Place a dry homogeneous mixture of 3 g of calcium fluoride powder (* what is it for?), powders 1 g of Cr 2 O 3 and 0.8 g of potassium dichromate, 0.5 g of freshly sawn aluminum powder. Make a hole in the middle, pour a mixture of magnesium powder and barium peroxide into it, and insert a long strip of magnesium into it. Place the crucible in a sand bath so that it is completely covered in sand. Using a burning torch inserted into a long glass tube, set fire to the magnesium strip. At the end of the reaction, let the crucible cool, break it and remove the chromium “kinglet”.

(photo by V. Bogdanov)

B) Aluminothermic production of iron

Place a dry homogeneous mixture of 1.8 g of iron (III) oxide and 0.5 g of freshly sawn aluminum powder into a fireclay crucible (or a pound made from asbestos). Make a hole in the middle and pour 0.8 g of potassium permanganate into it. In the middle of the pile of permanganate, use an empty test tube to make another hole. Place the crucible in a sand bath so that it is completely covered in sand. Pour a little glycerin on top so that it comes into contact only with the permanganate, but not with the surface of the reaction mixture. At the end of the reaction, let the crucible cool, break it and remove the “crown” of iron.

In most cases, the flame of a fireplace or fire is yellow-orange due to the salts contained in the wood. By adding certain chemicals, you can change the color of the flame to better suit a special event or to simply admire the changing colors. To change the color of the flame, you can add certain chemical compounds directly into the fire, prepare paraffin cakes with chemicals, or soak the firewood in a special chemical solution. Despite all the fun that creating colored flames can give you, be sure to take extra care when working with fire and chemicals.

Steps

Selecting the right chemicals

    Select the color (or colors) of the flame. Although you have a range of different flame colors to choose from, you need to decide which ones are most important to you so you can choose the right chemicals. The flame can be made blue, turquoise, red, pink, green, orange, purple, yellow or white.

    Determine the chemicals you need based on the color they create when burned. To color the flame the desired color, you need to select the right chemicals. They must be powdered and not contain chlorates, nitrates or permanganates, which form harmful by-products when burned.

    • To create blue flame, take copper chloride or calcium chloride.
    • To make the flame turquoise, use copper sulfate.
    • To obtain a red flame, take strontium chloride.
    • To create a pink flame, use lithium chloride.
    • To make the flames light green, use borax.
    • To obtain green flame, take alum.
    • To create an orange flame, use sodium chloride.
    • To create a flame purple take potassium chloride.
    • For getting yellow flame use sodium carbonate.
    • To create a white flame, use magnesium sulfate.

  1. Buy the right chemicals. Some of the flame coloring agents are common household chemicals and can be found at grocery, hardware, or garden stores. Other chemicals can be purchased at specialty chemical stores or purchased online.

    • Copper sulfate is used in plumbing to kill tree roots that can damage pipes, so you can look for it in hardware stores.
    • Sodium chloride is common table salt, so you can buy it at the grocery store.
    • Potassium chloride is used as a water softener, so it can also be found in hardware stores.
    • Borax is often used for laundry, so it can be found in the detergents some supermarkets.
    • Magnesium sulfate is contained in Epsom salt, which you can ask around in pharmacies.
    • Copper chloride, calcium chloride, lithium chloride, sodium carbonate and alum should be purchased from chemical stores or online retailers.

Adding chemicals to the fire

Making paraffin cakes

  1. Melt the paraffin in a water bath. Place a heatproof bowl over a pan of gently simmering water. Add a few pieces of paraffin wax to the bowl and let them melt completely.

    • You can use purchased lump or jar paraffin (or wax) or leftover paraffin from old candles.
    • Do not heat paraffin over an open flame, otherwise you may start a fire.

  2. Add the chemical to the paraffin and stir. Once the paraffin has completely melted, remove it from the water bath. Add 1–2 tablespoons (15–30 g) chemical reagent and stir thoroughly until a homogeneous mixture is obtained.

    • If you don't want to add the chemicals directly to the paraffin, you can first wrap them in used absorbent material and then place the resulting package in the container you are going to fill with paraffin.

  3. Let the paraffin mixture cool slightly and pour it into paper cups. After preparing the paraffin mixture with the chemical, let it cool for 5-10 minutes. While the mixture is still liquid, pour it into paper muffin cups to make wax cakes.

    • For cooking paraffin cakes You can use either small paper cups or egg cartons.

  4. Allow the paraffin to harden. After the paraffin is poured into the molds, let it sit until it hardens. It will take about an hour to cool completely.

    Throw the paraffin cake into the fire. When the paraffin cakes have hardened, remove one of them from the packaging. Throw the cake into the hottest part of the fire. As the wax melts, the flame will begin to change color.

    • You can add several paraffin cakes with different chemical additives to the fire at once, just place them in different places.
    • Paraffin cakes work well for fires and fireplaces.

Treatment of wood with chemicals

  1. Gather dry and light materials for the fire. Wood-based materials such as wood chips, lumber scraps, pine cones and brushwood are suitable for you. You can also use rolled newspapers.

    Dissolve the chemical in water. Add 450 g of the selected chemical for every 4 liters of water, use for this plastic container. Stir the liquid thoroughly to speed up the dissolution of the chemical. For best results, add only one type of chemical to the water.

    • You can also use a glass container, but avoid using metal containers, which may react with chemicals. Be careful not to drop or break glass containers in use near a fire or fireplace.
    • Be sure to wear safety glasses, a mask (or respirator), and rubber gloves when preparing the chemical solution.
    • It is best to prepare the solution for outdoors, as some types of chemicals may stain the work surface or release harmful fumes.

  2. Soak in the solution overnight wood materials. Pour the solution into a large container, e.g. Plastic container. Place the wood materials in a mesh bag (often used to store onions or potatoes) for submersion. Weigh down the bag with a brick or other heavy object and leave the wood in the liquid for 24 hours.

    Remove the mesh with wood materials from the solution and leave to dry. Lift the mesh bag containing the wood materials over the solution container to allow it to drain slightly. Then place the wood materials on a sheet of newspaper or hang them in a dry, well-ventilated area and allow to dry for 24 hours or more.

    • Be sure to wear protective gloves when removing wood materials from the chemical solution.
    • If you don't let the wood dry out, you'll have a hard time starting a fire.

  3. Burn treated wood materials in a fire. Build a fire or light a fireplace. Once the regular wood has burned through and the fire has subsided, add treated wood materials. After a few minutes they will light up and you will see colored flames.

Dyldina Yulia

The flame can have a different color, it all depends only on the metal salt that is added to it.

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MAOU secondary school No. 40

Subject

Flame coloring as one of the methods of analytical chemistry.

Dyldina Yudiya,

9th grade, MAOU Secondary School No. 40

Supervisor:

Gurkina Svetlana Mikhailovna,

Biology and chemistry teacher.

Perm, 2015

  1. Introduction.
  2. Chapter 1 Analytical chemistry.
  3. Chapter 2 Methods of analytical chemistry.
  4. Chapter 3 Flame coloring reactions.
  5. Conclusion.

Introduction.

From early childhood I was fascinated by the work of chemical scientists. They seemed like wizards who, having learned some hidden laws of nature, created the unknown. In the hands of these wizards, substances changed color, caught fire, heated or cooled, and exploded. When I came to chemistry lessons, the curtain began to rise, and I began to understand how chemical processes occur. The chemistry course I took was not enough for me, so I decided to work on a project. I wanted the topic I was working on to be meaningful, help me better prepare for the chemistry exam, and satisfy my craving for beautiful and vivid reactions.

Flame coloration by metal ions in different colors We study it in chemistry lessons when we cover alkali metals. When I became interested in this topic, it turned out that in this case, it was not fully disclosed. I decided to study it in more detail.

Target: With the help of this work I want to learn how to determine the qualitative composition of some salts.

Tasks:

  1. Get acquainted with analytical chemistry.
  2. Study the methods of analytical chemistry and choose the most suitable one for my work.
  3. Using an experiment, determine which metal is included in the salt.

Chapter 1.

Analytical chemistry.

Analytical chemistry -a branch of chemistry that studies the chemical composition and partly the structure of substances.

The purpose of this science is to determine chemical elements or groups of elements that make up substances.

The subject of its study is the improvement of existing and development of new methods of analysis, the search for opportunities for their practical application, and the study of the theoretical foundations of analytical methods.

Depending on the purpose of the methods, a distinction is made between qualitative and quantitative analysis.

  1. Qualitative analysis is a set of chemical, physicochemical and physical methods used to detect elements, radicals and compounds that are part of the analyzed substance or mixture of substances. In qualitative analysis, you can use easily feasible, characteristic chemical reactions in which the appearance or disappearance of color, the release or dissolution of a precipitate, the formation of gas, etc. are observed. Such reactions are called qualitative and with the help of them you can easily check the composition of a substance.

Qualitative analysis is most often carried out in aqueous solutions. It is based on ionic reactions and allows you to detect cations or anions of substances that are contained there. Robert Boyle is considered the founder of this analysis. He introduced this idea of ​​chemical elements as non-decomposable basic parts of complex substances, after which he systematized all qualitative reactions known in his time.

  1. Quantitative analysis is a set of chemical, physicochemical and physical methods for determining the ratio of components included in the composition

analyte. From the results of this, equilibrium constants, solubility products, molecular and atomic masses can be determined. Such an analysis is more difficult to perform, since it requires a careful and more painstaking approach; otherwise, the results may produce high errors and the work will be reduced to zero.

Quantitative analysis is usually preceded by qualitative analysis.

Chapter 2.

Methods of chemical analysis.

Chemical analysis methods are divided into 3 groups.

  1. Chemical methodsbased on chemical reactions.

In this case, only those reactions that are accompanied by a visible external effect can be used for analysis, for example, a change in the color of the solution, the release of gases, the precipitation or dissolution of precipitation, etc. These external effects will serve in this case as analytical signals. The chemical changes that occur are called analytical reactions, and the substances that cause these reactions are called chemical reagents.

All chemical methods are divided into two groups:

  1. The reaction is carried out in solution, the so-called “wet route”.
  2. A method of performing analysis on solids without the use of solvents is called the “dry route.” It is divided into pyro chemical analysis and analysis by trituration method. Atpyrochemical analysis andthe substance being tested is heated in a flame gas burner. In this case, volatile salts (chlorides, nitrates, carbonates) of a number of metals give the flame a certain color. Another method of pyrotechnic analysis is the production of colored pearls (glass). To obtain pearls, salts and metal oxides are fused with sodium tetraborate (Na2 B4O7 "10H2O) or sodium ammonium hydrogen phosphate (NaNH4HP04 4H20) and the color of the resulting glasses (pearls) is observed.
  3. Rubbing method was proposed in 1898 by F. M. Flavitsky. The solid test substance is ground with a solid reagent, and the external effect is observed. For example, cobalt salts with ammonium thiocyanate can give a blue color.
  1. When analyzed by physical methodsstudy physical properties substances using instruments without resorting to chemical reactions. Physical methods include spectral analysis, luminescence, X-ray diffraction and other methods of analysis.
  2. Using physico-chemical methodsstudy physical phenomena that occur in chemical reactions. For example, with the colorimetric method, the color intensity is measured depending on the concentration of the substance; in the conductometric analysis, the change in the electrical conductivity of solutions is measured.

Chapter 3.

Laboratory work.

Flame color reactions.

Target: To study the coloring of an alcohol lamp flame by metal ions.

In my work, I decided to use the method of pyrotechnic analysis of flame coloring with metal ions.

Test substances:metal salts (sodium fluoride, lithium chloride, copper sulfate, barium chloride, calcium chloride, strontium sulfate, magnesium chloride, lead sulfate).

Equipment: porcelain cups, ethyl alcohol, glass rod, concentrated hydrochloric acid.

To carry out the work, I made a solution of salt in ethyl alcohol and then set it on fire. I carried out my experiment several times, at the last stage the best samples were selected, after which we made a video.

Conclusions:

    Volatile salts of many metals color the flame in various colors characteristic of these metals. The color depends on the hot vapors of free metals, which are obtained as a result of the thermal decomposition of salts when they are introduced into the burner flame. In my case, these salts included sodium fluoride and lithium chloride; they gave bright, saturated colors.

Conclusion.

Chemical analysis is used by humans in many areas, but in chemistry lessons we only get acquainted with a small area of ​​this complex science. The techniques used in pyrochemical analysis are used in qualitative analysis as a preliminary test when analyzing a mixture of dry substances or as screening reactions. In qualitative analysis, “dry” reactions play only an auxiliary role; they are usually used as primary tests and verification reactions.

In addition, these reactions are used by humans in other industries, for example, in fireworks. As we know, fireworks are decorative lights of various colors and shapes, obtained by burning pyrotechnic compositions. So, pyrotechnicians add a variety of flammable substances to the composition of fireworks, among which non-metallic elements (silicon, boron, sulfur) are widely represented. During the oxidation of boron and silicon, it is released a large number of energy, but gas products are not formed, so these substances are used to make delayed-action fuses (to ignite other compounds at a certain time). Many mixtures include organic carbonaceous materials. For example, charcoal(used in black powder, fireworks shells) or sugar (smoke grenades). Chemically active metals are used (aluminum, titanium, magnesium), whose combustion during high temperature gives a bright light. This property was used to launch fireworks.

In the process of work, I realized how difficult and important it is to work with substances; not everything was as successful as I would have liked. As a rule, chemistry lessons lack practical work, thanks to which theoretical skills are developed. The project helped me develop this skill. In addition, it was with great pleasure that I introduced my classmates to the results of my work. This helped them consolidate their theoretical knowledge.

Question No. 1

BASIC CONCEPTS

Analytical chemistry is a branch of chemical science that develops on the basis of the fundamental laws of chemistry and physics principle methods and techniques for quality and quantitative analysis. Chemical analysis is understood as a set of actions aimed at obtaining information about the chemical composition of an object. Depending on the task at hand, the elemental, molecular, phase, isotopic, material composition, etc. are determined. Depending on the type of particles being identified, they are distinguished: elemental, molecular, functional, isotopic and phase analyses.

Elemental analysis is a qualitative and (most often) quantitative chemical analysis, as a result of which it is determined which chemical elements and in what quantitative ratios are included in the composition of the substance being analyzed.

^ Functional analysis– discovery and identification of various functional groups, for example, amino group NH 2, nitro group NO 2, carbonyl C=O, carboxyl COOH, hydroxyl OH, nitrile CN groups, etc.

^ Molecular analysis– discovery of molecules and determination of the molecular composition of the analyte, i.e. finding out what molecules and in what quantitative ratios a given analyzed object consists of.

^ Phase analysis– discovery and identification of various phases (solid, liquid, gaseous) included in the given analyzed system

Depending on the mass of dry matter or the volume of solution of the analyzed substance, analysis methods are divided into: macro-, semi-micro-, micro-, ultra-micro- and submicro-identification methods.
^

Characteristics of analysis methods based on sample size

For chemical identification, the reactions most often used are the formation of colored compounds, the release or dissolution of precipitates, gases, the formation of crystals of a characteristic shape, the coloring of a gas burner flame, the formation of compounds that luminesce in solutions.
^



Flame coloring with compounds of certain elements

Coloring a gas burner flame with metal compounds is used in qualitative analysis to discover metal cations that emit radiation in the visible region of the spectrum.

They say about analytical chemistry that it is the science of methods And means chemical analysis and, to a certain extent, the establishment of the chemical structure. By means we mean instruments, reagents, standard samples, computer programs, etc.

Methods And facilities are constantly changing: new approaches are involved, new principles of phenomena from different areas knowledge. Analytical chemistry is a field of scientific research, so awards have been awarded for the creation of many methods of analysis. Nobel Prizes(organic microanalysis, polarography, different types chromatographic analysis, photoelectron spectroscopy, etc.). It is necessary to distinguish between method and technique of analysis.

Substance analysis method - This short definition principles underlying the analysis of substances

Method of analysis - This detailed description all conditions and operations that ensure the correctness, reproducibility and other regulated characteristics of the analysis results.

Correctness of the analysis characterizes the quality of the analysis, reflecting the closeness to zero systematic error of the results.

Assay reproducibility – shows the degree of closeness to each other of the results of individual measurements (determinations) when analyzing samples.

In general, under analysis imply receiving empirically data on the chemical composition and quantity of a substance by any methods – physical, chemical, and physicochemical .

Modern analytical chemistry includes three sections: qualitative chemical analysis, quantitative chemical analysis and instrumental, i.e. physical and physicochemical methods. The separation of instrumental methods into a separate section is to some extent arbitrary, since with the help of these methods the problems of both qualitative and quantitative analysis are solved.

Qualitative chemical analysis – this is the determination (discovery) of chemical elements, ions, atoms, atomic groups, molecules in the analyzed substance.

Quantitative chemical analysis – this is a determination of the quantitative composition, i.e. establishing the number of chemical elements, ions, atoms, atomic groups, molecules in the analyzed substance.

When carrying out qualitative and quantitative analyses, analytical characteristics of substances and analytical reactions are used.

Analytical features - these are the properties of the analyzed substance or the products of its transformation, which make it possible to judge the presence of certain components in it.

Characteristic analytical features – color, smell, angle of rotation of the plane of polarization of light, radioactivity, ability to interact with electromagnetic radiation, etc. Analytical reaction - this is a chemical transformation of the analyte under the action of an analytical reagent with the formation of products with noticeable analytical characteristics.

The most commonly used reactions are:


  • Formation of colored compounds

  • Release or dissolution of sediments

  • Gas release

  • Formation of crystals of characteristic shape

  • Coloring a gas burner flame

  • Formation of compounds that luminesce in solutions

On the results of analytical reactions influenced by temperature, concentration of solutions, pH of the environment, the presence of other substances (interfering, masking, catalyzing processes)

Example:

1.
The copper ion Cu 2+ in aqueous solutions exists in the form of aqua complexes [Cu(H 2 O) m], when interacting with ammonia it acquires a soluble complex of a bright blue color:

[Сu(H 2 O) m ] + 4 NH 3 = 2+ + n H 2 O

2.
The Ba 2+ ion can be precipitated by adding a solution containing sulfate ions in the form of a slightly soluble white sediment Ba sulfate:

Ba 2+ + SO 4 2- → BaSO 4 ↓

The white precipitate of Ca 2+ carbonate dissolves under the action of acids, and carbon dioxide is released:

CaCO 3 + 2HCl → CaCl 2 + CO 2 + H 2 O

3.
If alkali is added to a solution of any ammonium salt, ammonia gas is released. It can be easily identified by its smell or by the blueness of wet red litmus paper:

NH 4 + + OH - = NH 3 . H 2 O → NH 3 + H 2 O

Sulfides, when exposed to acids, release hydrogen sulfide gas:

S 2- + 2H + = H 2 S

4.
Na+ ions in a drop of solution when interacting with hexahydroxostibate (V) – ions

They form white crystals of sodium hexahydroxostibate (V) Na with a characteristic shape:

Na + + - = Na

The shape of the crystal is clearly visible when viewed under a microscope.

This reaction is used to open the Na+ cation

5.
Coloring a gas burner flame with metal compounds is used to discover metal cations that produce radiation in the visible region of the spectrum. The coloring of the flame in one color or another depends on the nature of the metal.

6.
Sometimes analytical reactions are carried out, the products of which have luminescent properties in solutions. Thus, when the cation interacts with zinc uranyl acetate, a green glow of the solution is observed, and with sodium uranyl acetate in an acetic acid medium it gives yellow-green luminescence.

Question No. 2

Application of potentiometric and coulometric methods of analysis in pharmacy and analytical chemistry. The potentiometric method is a method of qualitative and quantitative analysis based on measuring the potentials that arise between the test solution and the electrode immersed in it. This method is recommended for establishing the quality and quantitative analysis of some pharmacopoeial drugs. I use potentiometric titration, it is possible to more objectively establish the equivalence point, so the method is widely used in practice. One of the directions of the potentiometric method is chronopotentiometry. The essence of this method is that the potential of one of the electrodes is recorded as a function of time. In addition to analytical purposes, the method can be used to study the kinetics of chemical processes. The potentiometric method can also be used to study the processes of destruction of medicinal substances during storage. The coulometric method is very promising for the analysis of medicinal substances: some local anesthetics, sulfonamides, alkaloids. The coulometric method is based on Faraday's law, which establishes a relationship between the amount of substance released on the electrodes and the amount of electricity spent on this process. Pharmaceutical analysis - determining the quality of drugs and medicines, manufactured by industry and pharmacies. Pharmaceutical analysis includes: analysis of drugs, medicinal raw materials, control of drug production, toxicological analysis of objects of plant and animal origin, forensic chemical analysis. To control the quality of medicines, pharmacopoeial methods of analysis are used - methods described in pharmacopoeial monographs approved at the state level or included in the State Pharmacopoeia - a collection of national standards and regulations regulating the quality of medicines. Pharmacopoeial analysis is quality control of medicinal raw materials, substances, dosage forms, carried out in accordance with the requirements of the Pharmacopoeia or individual pharmacopoeial articles not included in the Pharmacopoeia.

Question No. 3

An analytical sign is a visually observed, instrumentally recorded change in the properties of substances entering into analytical reactions. Analytical features include the following. 1. Formation (or dissolution) of a precipitate with certain properties: color, solubility in certain solvents, crystal shape. This may be the formation of a precipitate with a typical crystalline shape, characteristic color or appearance (for example, a white cheesy precipitate of AgCl). When separating, for example, zinc phosphate from aluminum phosphate, the ability of the zinc phosphate precipitate to dissolve in an aqueous ammonia solution to form CS is examined. 2. Obtaining a colored soluble compound under the action of a reagent, for example Cu(OH)2+4NH3=Cu(NH3)42 - blue copper ammonia. 3. Gas release from known properties. When CaCO3 and CaSO4 are dissolved in hydrochloric acid, in both cases a gas is released, which, when passed through barite water, forms outwardly identical precipitates of barium carbonate and barium sulfite, respectively. Therefore, barite water cannot distinguish between CO2 and SO2. If you pass each of the gases through a dilute solution of potassium permanganate acidified with sulfuric acid, then CO2 will not cause any changes in the color of the solution, and SO2 will react with potassium permanganate as a reducing agent: 2KMnO4 + 5S02 + 2H20 = 2MnS04 + K2S04 + 2H2S04, which will lead to the disappearance of the crimson color of the potassium permanganate solution. Qualitative analytical reactions are used to discover or detect ions or molecules of a substance. Chemical reaction, accompanied by an analytical sign (or analytical signal), by which one can judge the presence of the analyte, is called an analytical reaction. The analytical reaction must have a low detection limit. The detection limit is the smallest amount of a substance that can be determined by a given reaction with a given probability P. Qualitative analytical reactions are carried out by adding other substances called reagents to the solution of the analyzed substance. Analytical reactions can occur between liquids, solids and gaseous substances. Chemical analytical reactions are classified into general, group, selective and specific reactions. General reactions are reactions whose analytical signals are the same for many ions. The reagent used is also called the general reagent. Group reactions are a special case of general reactions used under specific conditions to isolate a specific group of ions with similar properties. General and group reactions are used to isolate and separate ions of a complex mixture. Selective, or selective, are reactions that allow the detection of a limited number of cations or anions in a mixture of ions. Thus, when NH.SCN acts on a mixture of cations, only two cations form soluble colored complex compounds: 3_ and (Co(SCN),]2-. Analytical reactions are called specific, the analytical effect of which is characteristic of only one ion in the presence of other ions. Selective and specific reactions in qualitative analysis are called qualitative characteristic (or particular) reactions

The analytical reaction must meet certain requirements. It should not proceed too slowly and be fairly simple to implement. For analytical reactions the most important requirements are specificity and sensitivity. The fewer ions that react with a given reagent, the more specific the reaction. The smaller the amount of a substance that can be determined using a given reagent, the more sensitive the reaction. The sensitivity of a reaction can be characterized quantitatively using two indicators: the opening minimum and the dilution limit. The opening minimum is the smallest amount of a substance or ion that can be opened by a given reagent under given conditions. The limiting dilution characterizes the lowest concentration of a substance (or ion) at which it is still possible to open it with a given reagent.

Question #4

Preparing the sample for analysis. If quantitative measurements are carried out in solution, the sample is dissolved in a suitable solvent; in this case, the sample concentration is selected so that it is within the applicability limits of the method. Sometimes it is necessary to isolate the analyte from a mixture, since many analytical methods are nonspecific and even nonselective. A specific method is a method by which only a specific substance is determined, while a selective method is one that is preferable for of this substance a method that can be used to determine other substances. There are very few specific methods, much more selective ones. For example, mass spectrometry and immunoassay are highly selective.

“Dissolution of the sample”), or by converting the sample into a soluble substance, for example, by melting it with soda, potash, sodium hydrogen sulfate, alkalis, etc.

If a solvent is not found, then the analyzed precipitate is converted by heating or fusion with one or another reagent into soluble reaction products and these products are dissolved in water or acids.

When the analyzed sample contains sulfates of lead and cations of the third analytical group, insoluble in acids, they can be converted into acid-soluble carbonates by boiling with a saturated aqueous solution of soda Na2CO3 and potash K2CO3 or by fusion with a mixture of Na2CO3 and K2CO3.

b) Melting with a mixture of soda and potash.

When fused, sulfates are converted into carbonates, as when boiling (see.

Fusion of a solid with reagents.

With this fusion, the components of the solid sample being analyzed, insoluble in water and in acids, are converted into reaction products that are soluble in acids.

So, for example, silicon dioxide and insoluble silicates, when fused (preferably in a platinum crucible) with a mixture of soda and potash, turn into soluble sodium or potassium silicates and the corresponding carbonates:

can be converted into soluble reaction products by fusion with KHSO4 or K2S2O7 (in quartz crucibles with lids), for example:

Some metal oxides also turn into soluble salts when fused with soda, for example:

In many other cases, methods and techniques are described for converting insoluble samples into soluble reaction products by fusing solid phases with various reagents.

If a solid sample does not dissolve in any of the solvents used, then in some cases it is converted into a soluble state by treatment when heating (usually repeated) with saturated solutions of soda Na2C03, potash K2C03, or by fusing part of the sample with these salts or hydrogen sulfates alkali metals(NaNZOD with potassium pyrosulfate K2S207, with alkalis and other substances.

Question #5

There is no precise data in the literature about the time of the birth of toxicological (forensic) chemistry as a science in Russia. There is only information according to which the first chemical studies of a forensic chemical nature were carried out in Russia back in the 15th century. At that time there were no chemical laboratories to study various objects for the presence of poisons. Forensic chemical studies were random in nature and were carried out in pharmacies.

At the end of the 16th - beginning of the 17th century. In Russia, the Pharmacy Order was established (data on exact date The institutions of the Pharmacy Order are contradictory), which is the highest medical administrative institution of pre-Petrine Rus'. The Pharmacy Order supervised medical and pharmacy practice in Russia. He was in charge of a laboratory in which medications, drinks, vodka, etc. In the same laboratory and in pharmacies, individual forensic chemical studies were occasionally carried out. However, even during the period of the Pharmacy Order, forensic medical and forensic chemical examinations were not legalized.

The first document that legalized forensic medical examination in Russia was the Military Regulations, issued by Peter I in 1716. As M. D. Shvaikova points out, forensic chemical examination in Russia was probably legalized along with forensic medicine. However, even after the publication of the Military Regulations, autopsies of corpses were not carried out everywhere. The corpses were opened in Moscow and St. Petersburg hospitals, and then autopsies gradually began to be performed in other cities of Russia.

In 1797, medical councils were established in many provinces to manage all medical activities, including ensuring the conduct of forensic medical research. At these boards, the position of a full-time pharmacist was established, who was supposed to carry out chemical research and detect poisons. There were no laboratories at the medical boards. Therefore, staff pharmacists carried out research on poisons in private laboratories or pharmacies.

The creation by M.V. Lomonosov in 1748 of the first Russian chemical laboratory was an important event in the development of Russian science. The laboratory had a great influence on the development of chemistry in general, including the development of analytical chemistry, the methods of which were widely used in forensic chemical analyses.

Despite some advances in the field of forensic chemistry, until early XIX Art. it developed slowly. The scientific and theoretical level of methods used in expert practice was low. At that time, there was no qualified forensic chemist workforce. Forensic chemistry was not taught in universities and other educational institutions. Due to the low level of development of analytical chemistry, there were no methods for detecting many poisons. There were no textbooks or manuals on forensic chemistry.

XIX century characterized by a significant improvement in the state of forensic chemical research. In 1808, a pharmaceutical department was opened at the medical faculty of Moscow University. The subject “pharmacy” was included in the curriculum of this department. While studying this subject Special attention focused on toxicology and detection of poisons. The same department was opened in St. Petersburg at the Medical-Surgical Academy. Somewhat later, pharmaceutical departments were opened at other universities.

With the development of pharmaceutical education in Russia, a cadre of scientists has grown, whose works have enriched forensic chemistry with new methods of analysis. Textbooks and manuals on forensic chemistry appeared.

One of the first Russian scientists to enrich forensic chemistry with new reactions and methods of analysis was A.P. Nelyubin (1785-1858), who was a doctor and pharmacist by training. He headed the Department of Pharmacy at the Medical-Surgical Academy. A.P. Nelyubin performed a large number of tests for the presence of poisons. He was the first to propose a method for destroying biological material containing “metal poisons” with nitric acid. He proposed a method for detecting arsenic compounds by converting them into arsenous hydrogen. A.P. Nelyubin summarized his rich experience in the field of forensic chemical analysis in his work “Rules for guiding a forensic doctor in the study of poisoning,” published in 1824 in the Military Medical Journal. In this work, the scientist devoted great attention research of poisons.

A.P. Nelyubin was the author of the manual “General and private forensic and police chemistry with the addition of general toxicology or the science of poisons and antidotes.” At that time, police chemistry meant sanitary chemical analysis (food analysis).

A prominent scientist in the field of forensic chemistry was Prof. A. A. Iovsky (1796-1857). At Moscow University he lectured on general and analytical chemistry, pharmacology and toxicology. A. A. Iovsky was the author of about 40 works devoted to various sections of pharmacy. In 1834, his book “Guide to the recognition of poisons, antidotes and the most important determination of the former both in the body and outside it through chemicals, called reagents."

Prof. made a great contribution to the development of pharmacy and forensic chemistry. Yu. K. Trapp (1814-1908), who was a student of A. P. Nelyubin. While working at the Medical-Surgical Academy, Yu. K. Trapp analyzed various objects for the presence of poisons, studied false signatures, ink stains, charred banknotes, etc.

Y. K. Trapp was the author of books on forensic chemistry. In 1863, his book “Manual for the first aids in poisoning and for the chemical study of poisons” was published, and in 1877 the book “Manual for forensic chemical research” was published.

A certain contribution to the development of forensic chemistry was made by the professor of Dorpat (currently Tartu) University G. Dragendorf (1836-1898). He proposed a reagent for the detection of alkaloids and developed a method for isolating alkaloids from biological material, based on isolating these substances with water acidified with sulfuric acid. G. Dragendorff published the textbook “Forensic Chemical Discovery of Poisons” and was the first scientist who separated forensic chemistry from pharmacy and read it as an independent discipline.

A number of works in the field of forensic chemistry were carried out by G. V. Struve (1822-1908), who was a generalist. His work is devoted to the development of forensic, analytical and biological chemistry. G.V. Struve proposed reactions for the detection of arsenic and phosphorus compounds with molybdate, and improved methods for the detection of cyanides, morphine, strychnine and some other alkaloids. He has performed a number of complex examinations in the field of detecting poisons in biological material. Part of his work is devoted to the study of food falsification, etc.

In the XIX century. A number of important studies in the field of forensic chemistry were carried out by scientists who worked in other areas of chemistry. These include: T. E. Lovitz, N. N. Zinin, D.I. Mendeleev and others. T.E. Lovitz (1757-1804) performed a number of examinations to establish the causes of poisoning. N. N. Zinin (1812-1880) carried out examinations, the purpose of which was to establish the poor quality of wines and determine the presence of blood stains

On some items, determination of impurities in Chinese tea, etc. He performed a number of examinations to establish the causes of poisoning.

D. I. Mendeleev (1834-1907) performed a number of examinations on the instructions of judicial investigative authorities. At the Medical Department of the Ministry of Internal Affairs, for many years he was a member of the medical council, which at that time was the highest judicial expert authority in Russia.

A major role in conducting research in the field of forensic chemistry belongs to Prof. S.P. Dvornichenko, who summarized his own research data and literature data in the field of forensic chemical analysis and in 1900 published a manual on forensic chemistry.

A major role in the development of domestic forensic chemistry belongs to Prof. A. P. Dianil (1851 -1918). For more than thirty years he worked at the Medical-Surgical Academy. During this time, A.P. Dianin performed about 5,000 tests. He combined his work at the academy with work in the Medical Department of the Ministry of Internal Affairs. In 1904, A.P. Dianin was appointed chief forensic chemical expert.

Great October socialist revolution made fundamental changes in all areas public life and in the development of science in our country. The organization of forensic medical and forensic chemical examinations has changed. Forensic medical examination became a reliable assistant to the Soviet justice authorities in strengthening socialist legality.

In 1918, a medical examination department was established under the People's Commissariat of Health of the RSFSR. Similar departments were created under the provincial health authorities. After some time, the positions of provincial and city forensic experts were introduced, and provincial forensic laboratories were also organized.

In 1924, a central forensic laboratory was created in Moscow, transformed in 1932 into the State Research Institute of Forensic Medicine. To manage forensic and forensic chemical examinations in our country, in 1937, the position of chief forensic medical expert was introduced under the USSR People's Commissariat of Health.

In 1934, the People's Commissar of Health of the RSFSR, in agreement with the prosecutor's office of the RSFSR, approved the “Rules for forensic medical and forensic chemical examination of material evidence.” In 1939, the Council of People's Commissars of the USSR adopted a resolution “On measures to strengthen and develop forensic medical examination.” In 1952, the USSR Ministry of Health, in agreement with the USSR Prosecutor's Office, the Ministry of Justice and the USSR Ministry of State Security, approved the “Instructions on the conduct of forensic medical examinations in the USSR.”

In 1957, the USSR Ministry of Health, in agreement with the USSR Prosecutor's Office and the USSR Ministry of Internal Affairs, approved new rules for the forensic chemical examination of material evidence in the forensic chemical departments of forensic laboratories.

In 1962, the order of the USSR Minister of Health “On measures to improve forensic medical examination in the USSR” was issued. In 1978, the USSR Ministry of Health approved new instructions on the production of forensic medical examination, regulations on the forensic medical examination bureau and its officials. Behind Lately In addition to the documents listed above, a number of provisions were approved aimed at improving the quality of forensic medical and forensic chemical examinations in the USSR.

A large role in the further development of forensic chemistry belongs to a number of domestic scientists and higher pharmaceutical educational institutions.

In 1920, the first departments of forensic chemistry were created at the Chemical-Pharmaceutical Faculty of the Second Moscow University and at the Petrograd Chemical-Pharmaceutical Institute, which became the center scientific research in the field of forensic chemical analysis and a center for the training of chemical experts. Somewhat later, departments of forensic chemistry were created in other institutes.

For a number of years, the Department of Forensic Chemistry at the Leningrad Chemical-Pharmaceutical Institute was headed by Prof. L. F. Ilyin (1872-1937). He is the author of a number of works on forensic chemistry. Several dissertations were completed under his supervision.

In the development of forensic chemistry, a certain role belongs to prof. N.I. Kromer (1866-1941), who taught at the Perm Pharmaceutical Institute, and prof. N. A. Valyashko (1871 - 1955). For 15 years, N. A. Valyashko was a consultant to the chemical department of the Kharkov Scientific Research Institute of Forensic Science of the Ministry of Justice. During this time, he published a number of works on forensic chemical analysis. Under the guidance of prof. N. A. Valyashko completed and defended the thesis of T. V. Marchenko, which long years was the head of the department of forensic chemistry at the Kharkov Pharmaceutical Institute.

Prof. A. V. Stepanov (1872-1946) created and headed the department of forensic chemistry at the Moscow Pharmaceutical Institute. He was one of the organizers of this institute.

The scientific and pedagogical activities of A. V. Stepanov relate to judicial and organic chemistry. He developed a method for determining chlorinated derivatives organic compounds, which is still widely used in the analysis of organic halogen-containing substances. A. V. Stepanov proposed a mineralization method

Biological material with a mixture of ammonium nitrate and sulfuric acid. Together with M. D. Shvaikova, he developed a high-speed method for isolating alkaloids from food products plant origin. He published works on forensic chemical analysis and published a textbook on forensic, organic and analytical chemistry. His textbook “Forensic Chemistry” was published four times.

From 1937 to 1978, the department of forensic chemistry at the Moscow Pharmaceutical Institute (then at the faculty of the First Moscow Medical Institute) was headed by Professor M. D. Shvaikova (1905-1978), a student of Prof. A. V. Stepanova.

The area of ​​scientific research of M. D. Shvaikova is large. Together with prof. She proposed a high-speed method for isolating alkaloids from food products of plant origin to A.V. Stepanov. M.D. Shvaikova is the founder of the use of the microcrystalloscopy method in forensic chemical analysis; under her leadership, research was also carried out in the field of forensic chemical analysis of “metal poisons,” alkaloids, barbiturates and many other toxic compounds. This is a great contribution to forensic chemical analysis.

A major role in the development of forensic medicine and forensic chemistry belongs to the Scientific Research Institute of Forensic Medicine of the USSR Ministry of Health, which was organized in 1932. The Institute manages research work in the field of forensic medicine and forensic chemistry, and also carries out complex and repeated examinations on instructions from judicial investigative authorities.

Employees of the chemical department of this institute developed a method for the quantitative determination of mercury in biological material, a method for isolating alkaloids from biological material, based on isolating them with water acidified with oxalic acid, a fractional method for forensic chemical research of “metal poisons” was developed and put into practice, methods were developed forensic chemical analysis of a number of glycosides; research is carried out on the analysis of pesticides and other toxic substances, phenothiazine derivatives.

Employees of the chemical department of the Research Institute of Forensic Medicine published a number of methodological letters and guidelines dedicated to the study toxic substances in cadaveric material. The methods outlined in these letters are widely used in forensic chemical laboratories of the USSR.

A certain contribution to the development of toxicological chemistry was made by the departments of the Lvov Medical Institute, Tashkent and Pyatigorsk Pharmaceutical Institutes, as well as other educational institutions.

In 1939, the Department of Forensic (Toxicological) Chemistry was organized at the Faculty of Pharmacy of the Lvov Medical Institute. Since 1948, the department was headed by prof. V. F. Krama-renko. The scientific direction of the department is the development of methods for chemical and toxicological analysis of alkaloids, their synthetic analogues and barbiturates. V. F. Kramarenko is

by about 200 scientific works devoted to the use of chemical, physical and physicochemical methods of analysis (photocolorimetry, spectrophotometry, chromatography in thin layers sorbents, gel chromatography, gas-liquid chromatography, etc.) in toxicological chemistry. He proposed a method for isolating alkaloids from biological material, based on isolating them with water acidified with sulfuric acid

.

A major role in the development of toxicological chemistry in our country belongs to the chemical department (department head A.F. Rubtsov) of the State Research Institute of Forensic Medicine of the USSR Ministry of Health. This institute has developed a number of new methods for studying toxic substances. Published guidelines on the study of several poisons in objects subjected to chemical and toxicological analysis.

In the post-war years, progress was made in training scientific personnel in toxicological (forensic) chemistry. So, at the Moscow Pharmaceutical Institute, and then at the Faculty of Pharmacy of the First Moscow Medical Institute under the leadership of prof. M. D. Shvaikova completed and defended six doctoral and forty candidate dissertations. At the same department, under the leadership of Assoc. B. N. Izotov completed and defended 12 candidate dissertations.

At the Lviv Medical Institute, under the guidance of prof. V. F. Kramarenko prepared and defended five doctoral and 31 candidate dissertations. At the same department under the leadership of prof. V. I. Popova defended four Ph.D. dissertations. Nine candidate dissertations were defended under the guidance of Associate Professor A.F. Rubtsov. The same number of dissertations were defended at the Tashkent Pharmaceutical Institute under the guidance of prof. L. T. Ikramova.

At the Department of Toxicological Chemistry of the Tashkent Pharmaceutical Institute, a number of studies were carried out, mainly devoted to the analysis of pesticides.

Research in the field of analysis of toxic substances is carried out at the departments of toxicological chemistry of pharmaceutical and other institutes.

The results of chemical toxicological analysis depend on the right choice objects of study, compliance with the rules of chemical and toxicological analysis of biological material for the presence of toxic substances, the correct choice of research methods and some other factors.