Analysis method name the principles underlying the analysis of matter, that is, the type and nature of the energy that causes disturbance of the chemical particles of the substance.

The analysis is based on the relationship between the detected analytical signal and the presence or concentration of the analyte.

Analytical signal is a fixed and measurable property of an object.

IN analytical chemistry analysis methods are classified according to the nature of the property being determined and the method of recording the analytical signal:

1.chemical

2.physical

3.physical and chemical

Physicochemical methods are called instrumental or measuring methods, since they require the use of instruments and measuring instruments.

Let's consider the complete classification of chemical methods of analysis.

Chemical methods of analysis- based on energy measurement chemical reaction.

During the reaction, parameters associated with the consumption of starting materials or the formation of reaction products change. These changes can either be observed directly (precipitate, gas, color) or measured by quantities such as reagent consumption, mass of product formed, reaction time, etc.

By goals chemical analysis methods are divided into two groups:

I.Qualitative analysis- is to detect individual elements(or ions) that make up the analyte.

Methods qualitative analysis classified:

1. cation analysis

2. Anion analysis

3. analysis of complex mixtures.

II.Quantitative analysis– consists in determining the quantitative content of individual components complex substance.

Quantitative chemical methods classify:

1. Gravimetric(weight) method of analysis is based on the isolation of the analyte in pure form and weighing it.

Gravimetric methods are divided according to the method of obtaining the reaction product:

a) chemogravimetric methods are based on measuring the mass of the product of a chemical reaction;

b) electrogravimetric methods are based on measuring the mass of the product of an electrochemical reaction;

c) thermogravimetric methods are based on measuring the mass of a substance formed during thermal exposure.

2. Volumetric analysis methods are based on measuring the volume of the reagent spent on interaction with the substance.

Volumetric methods, depending on the state of aggregation of the reagent, are divided into:

a) gas-volumetric methods, which are based on the selective absorption of the component being determined gas mixture and measuring the volume of the mixture before and after absorption;

b) liquid-volumetric (titrimetric or volumetric) methods are based on measuring the volume of liquid reagent consumed for interaction with the substance being determined.

Depending on the type of chemical reaction, volumetric analysis methods are distinguished:

· protolitometry – a method based on the occurrence of a neutralization reaction;

· redoxometry – a method based on the occurrence of redox reactions;

· complexometry – a method based on the occurrence of a complexation reaction;

· precipitation methods – methods based on the occurrence of precipitation formation reactions.

3. Kinetic analytical methods are based on determining the dependence of the rate of a chemical reaction on the concentration of reactants.

Lecture No. 2. Stages of the analytical process

The solution to the analytical problem is carried out by performing an analysis of the substance. According to IUPAC terminology analysis [‡] called the procedure for obtaining empirical data about chemical composition substances.

Regardless of the chosen method, each analysis consists of the following stages:

1) sampling (sampling);

2) sample preparation (sample preparation);

3) measurement (definition);

4) processing and evaluation of measurement results.

Fig1. Schematic representation of the analytical process.

Sample selection

Chemical analysis begins with the selection and preparation of a sample for analysis. It should be noted that all stages of analysis are interconnected. Thus, a carefully measured analytical signal does not give correct information about the content of the component being determined if the sample was selected or prepared incorrectly for analysis. Sampling error often determines the overall accuracy of component determination and makes the use of highly accurate methods pointless. In turn, sample selection and preparation depend not only on the nature of the analyzed object, but also on the method of measuring the analytical signal. The techniques and procedures for sample collection and preparation are so important in chemical analysis that they are usually prescribed State standard(GOST).

Let's consider the basic rules for sampling:

· The result can only be correct if the sample is sufficiently representative, that is, it accurately reflects the composition of the material from which it was selected. The more material selected for the sample, the more representative it is. However, very large samples are difficult to handle and increase analysis time and costs. Thus, the sample must be taken so that it is representative and not very large.

· The optimal sample mass is determined by the heterogeneity of the analyzed object, the size of the particles from which the heterogeneity begins, and the requirements for the accuracy of the analysis.

· To ensure the representativeness of the sample, batch homogeneity must be ensured. If it is not possible to form a homogeneous batch, then the batch should be separated into homogeneous parts.

· When taking samples, the aggregate state of the object is taken into account.

· The condition for the uniformity of sampling methods must be met: random sampling, periodic, chess, multi-stage sampling, “blind” sampling, systematic sampling.

· One of the factors that must be taken into account when choosing a sampling method is the possibility of changes in the composition of the object and the content of the component being determined over time. For example, the variable composition of water in a river, changes in the concentration of components in food products etc.

MOSCOW AUTOMOBILE AND ROAD ROAD INSTITUTE (STATE TECHNICAL UNIVERSITY)

Department of Chemistry

I approve the Head. professor at the department

I.M. Papisov "___" ____________ 2007

A.A. LITMANOVICH, O.E. LITMANOVICH

ANALYTICAL CHEMISTRY Part 1. Qualitative chemical analysis

Toolkit

for second year students of the specialty “Engineering Protection” environment”

MOSCOW 2007

Litmanovich A.A., Litmanovich O.E. Analytical chemistry: Part 1: Qualitative chemical analysis: Methodological manual / MADI

(GTU) - M., 2007. 32 p.

The basic chemical laws of qualitative analysis of inorganic compounds and their applicability for determining the composition of environmental objects are considered. The manual is intended for students of the specialty “Engineering Environmental Protection”.

© Moscow Automobile and Highway Institute (state Technical University), 2008

CHAPTER 1. SUBJECT AND TASKS OF ANALYTICAL CHEMISTRY. ANALYTICAL REACTIONS

1.1. Subject and tasks of analytical chemistry

Analytical chemistry– the science of methods for studying the composition of substances. Using these methods, it is determined which chemical elements, in what form and in what quantity they are contained in the object being studied. In analytical chemistry there are two large sections - qualitative and quantitative analysis. Analytical chemistry solves the assigned problems using chemical and instrumental methods (physical, physicochemical).

IN chemical methods analysis the element being determined is converted into a compound that has properties that can be used to establish the presence of this element or measure its quantity. One of the main ways to measure the amount of a compound formed is to determine the mass of the substance by weighing on an analytical balance - the gravimetric method of analysis. Methods of quantitative chemical analysis and instrumental methods of analysis will be discussed in part 2 methodological manual in analytical chemistry.

A current direction in the development of modern analytical chemistry is the development of methods for analyzing environmental objects, waste and waste waters, gas emissions industrial enterprises And road transport. Analytical control makes it possible to detect excess content of particularly harmful components in discharges and emissions, and helps to identify sources of environmental pollution.

Chemical analysis is based on the fundamental laws of general and inorganic chemistry, with which you are already familiar. Theoretical basis chemical analysis include: knowledge of the properties of aqueous solutions; acid-base equilibrium in water

solutions; redox equilibria and properties of substances; patterns of complex formation reactions; conditions for the formation and dissolution of the solid phase (precipitates).

1.2. Analytical reactions. Conditions and methods of their implementation

Qualitative chemical analysis is carried out using analytical reactions, accompanied by noticeable external changes: for example, the release of gas, a change in color, the formation or dissolution of a precipitate, in some cases - the appearance of a specific odor.

Basic requirements for analytical reactions:

1) High sensitivity, characterized by the detection limit value (Cmin) - the lowest concentration of a component in a solution sample at which this technique analysis allows you to confidently detect this component. The absolute minimum value of the mass of a substance that can be detected by analytical reactions is from 50 to 0.001 μg (1 μg = 10–6 g).

2) Selectivity– characterized by the ability of a reagent to react with as few components (elements) as possible. In practice, they try to detect ions under conditions under which the selective reaction becomes specific, i.e. allows you to detect a given ion in the presence of other ions. As examples of specific reactions(of which there are few) the following can be cited.

a) Interaction of ammonium salts with excess alkali when heated:

NH4 Cl + NaOH → NH3 + NaCl + H2 O. (1)

The ammonia released is easily recognized by its characteristic odor (“ ammonia") or by a change in the color of wet indicator paper brought to the neck of the test tube. Reaction

allows you to detect the presence of ammonium ions NH4 + in the analyzed solution.

b) Interaction of ferrous iron salts with potassium hexacyanoferrate (III) K3 with the formation of a precipitate of blue color(Turnbull's blue, or Prussian blue). Reaction (well familiar to you on the topic “Corrosion of Metals” in the course

These reactions make it possible to detect Fe2+ and Fe3+ ions in the analyzed solution.

Specific reactions are convenient because the presence of unknown ions can be determined by a fractional method - in separate samples of the analyzed solution containing other ions.

3) The speed of the reaction ( high speed ) and ease of implementation.

The high reaction rate ensures that thermodynamic equilibrium is achieved in the system within a short time(almost at the rate of mixing of components during reactions in solution).

When performing analytical reactions, it is necessary to remember what determines the shift in the equilibrium of the reaction in the desired direction and its occurrence to a large depth of transformation. For reactions occurring in aqueous solutions of electrolytes, the shift in thermodynamic equilibrium is influenced by the concentration of ions of the same name, pH of the medium, and temperature. In particular, it depends on temperature the value of the equilibrium constants – constants

dissociation for weak electrolytes and solubility product (SP) for poorly soluble salts and bases

These factors determine the depth of the reaction, the yield of the product and the accuracy of determining the analyte (or the very possibility of detecting a specific ion at a small amount and concentration of the analyte).

The sensitivity of some reactions increases in an aqueous organic solution, for example, when acetone or ethanol is added to an aqueous solution. For example, in an aqueous-ethanol solution, the solubility of CaSO4 is significantly lower than in an aqueous one (the PR value is smaller), which makes it possible to unambiguously detect the presence of Ca2+ ions in the analyzed solution at much lower concentrations than in an aqueous solution, and also to most completely free the solution from these ions (precipitation with H2 SO4) to continue analyzing the solution.

With high quality chemical analysis A rational sequence in the separation and detection of ions is being developed - a systematic flow (scheme) of analysis. In this case, ions are isolated from the mixture in groups, based on their identical relationship to the action of certain group reagents.

One portion of the analyzed solution is used, from which groups of ions are sequentially isolated in the form of precipitates and solutions, in which individual ions are then detected . The use of group reagents makes it possible to decompose the complex task of qualitative analysis into a number of simpler ones. The ratio of ions to the action of certain

group reagents are the basis analytical classification of ions.

1.3. Preliminary analysis of an aqueous solution containing a mixture of salts by color, smell, pH value

The presence of color in a transparent solution proposed for analysis may indicate the presence of one or several ions at once (Table 1). The intensity of the color depends on the concentration of the ion in the sample, and the color itself can change if

Metal cations form more stable complex ions than complex cations with H2 O molecules as ligands, for which the color of the solution is indicated in Table. 1 .

		Table 1
Solution color	Possible cations	Possible
Turquoise	Cu2+
	Cr3+
	Ni2+	MnO4 2-
	Fe3+ (due to hydrolysis)	CrO4 2- , Cr2 O7 2-
	Co2+	MnO4 -

Measuring the pH of the proposed solution ( if the solution is prepared in water, and not in a solution of alkali or acid) also

gives additional		information about			possible composition
						table 2
Own				Possible		Possible
water pH
nogo sol-
	Hydrolysis			Na+ , K+ , Ba2+ ,		SO3 2- , S2- , CO3 2- ,
	educated			Ca2+		CH3 COO-
				metals s-		(corresponding
	basis			electronic		acids – weak
	weak acid			families)		electrolytes)
	Hydrolysis			NH4+		Cl-, SO4 2-, NO3 -, Br-
	educated					(corresponding
				practically
	acid
				metals		electrolytes)
	basis
	Hydrolysis			Al3+, Fe3+
	grounds

Aqueous solutions of some salts may have specific odors depending on the pH of the solution due to the formation of unstable (decomposing) or volatile compounds. By adding NaOH solutions or

strong acid (HCl, H2 SO4), you can gently sniff the solution (Table 3).

Table 3

pH of the sample solution			Corresponding ion
after adding
			in solution
	Ammonia		NH4+
	(smell of ammonia)
		unpleasant	SO3 2-
	smell (SO2)
	"Vinegar"	(acetic	CH3 COO-
	acid CH3 COOH)
	(hydrogen sulfide H2S)

The cause of the odor (see Table 3) is good known property reactions in electrolyte solutions - displacement of weak acids or bases (often aqueous solutions of gaseous substances) from their salts by strong acids and bases, respectively.

CHAPTER 2. QUALITATIVE CHEMICAL ANALYSIS OF CATIONS

2.1. Acid-base method for classifying cations into analytical groups

The simplest and least “harmful” acid-base (basic) method of qualitative analysis is based on the ratio of cations to acids and bases. Cations are classified according to the following criteria:

a) solubility of chlorides, sulfates and hydroxides; b) basic or amphoteric nature of hydroxides;

c) the ability to form stable complex compounds with ammonia (NH3) - ammonia (i.e. ammine complexes).

All cations are divided into six analytical groups using 4 reagents: 2M HCl solution, 1M H2SO4 solution, 2M NaOH solution and concentrated aqueous ammonia solution

NH4 OH (15-17%) (Table 4).

Table 4 Classification of cations by analytical groups

	Group		Result
			group actions
			reagent
		Ag+, Pb2+	Precipitate: AgCl, PbCl2
	1M H2SO4	(Pb2+), Ca2+,	Precipitate (white): BaSO4,
		Ba2+	(PbSO4), CaSO4
		Al3+ , Cr3+ , Zn2+	Solution: [Аl(OH)4 ]– ,
	(excess)		– , 2–
	NH4OH (conc.)	Fe2+, Fe3+, Mg2+,	Precipitate: Fe(OH)2,
		Mn2+	Fe(OH)3, Mg(OH)2,
			Mn(OH)2
	NH4OH (conc.)	Cu2+, Ni2+, Co2+	Solution (colored):
			2+, blue
			2+, blue
			2+, yellow (on
			the air turns blue due to
			oxidation to Co3+)
	Absent	NH4 + , Na+ , K+

Obviously, the given list of cations is far from complete and includes the cations most frequently encountered in practice in the analyzed samples. In addition, there are other principles of classification by analytical groups.

2.2. Intragroup analysis of cations and analytical reactions for their detection

2.2.1. First group (Ag+, Pb2+)

Test solution containing cations Ag+, Pb2+

↓ + 2M solution of HCl + C 2 H5 OH (to reduce the solubility of PbCl2)

If PC > PR, white precipitates of a mixture of chlorides,

which are separated from the solution (the solution is not analyzed):

Ag+ + Cl– ↔ AgCl↓ and Pb2+ + 2Cl– ↔ PbCl2 ↓ (3)

It is obvious that at low concentrations of precipitated cations, the concentration of Cl– anions should be relatively high

↓ To part of the sediment + H2 O (distilled) + boiling

Partially goes into solution	The sediment contains all AgCl and
Pb 2+ ions (equilibrium shift	partially PbCl2
(3) to the left, because PC< ПР для PbCl2 )
	↓ + NH4 OH (conc.)
Detection in solution,
	1. Dissolution of AgCl due to
separated from the sediment:	complexation:
1. With reagent KI (after	AgCl↓+ 2NH4 OH(g) →
cooling):	→+ +Cl– +2H2 O
Pb2+ + 2I– → PbI2 ↓ (golden
crystals) (4)
	↓+ 2M HNO3 solution
	↓ to pH<3
	2. Precipitation of AgCl due to
	decay of a complex ion:
	Cl– + 2HNO3
	→AgCl↓+ 2NH4 + + 2NO3

↓ To the 2nd part of the sediment of a mixture of chlorides + 30%

Its subject as a science is the improvement of existing and development of new methods of analysis, their practical application, and the study of the theoretical foundations of analytical methods.

Depending on the task, analytical chemistry is subdivided into qualitative analysis, aimed at determining whether What or which substance, in what form it is in the sample, and quantitative analysis aimed at determining How many of a given substance (elements, ions, molecular forms, etc.) is in the sample.

Determining the elemental composition of material objects is called elemental analysis. Establishing the structure of chemical compounds and their mixtures at the molecular level is called molecular analysis. One of the types of molecular analysis of chemical compounds is structural analysis, aimed at studying the spatial atomic structure of substances, establishing empirical formulas, molecular masses, etc. The tasks of analytical chemistry include determining the characteristics of organic, inorganic and biochemical objects. Analysis of organic compounds by functional groups is called functional analysis.

Story

Analytical chemistry has existed as long as chemistry has existed in its modern sense, and many of the techniques used in it date back to an even earlier era, the era of alchemy, one of the main tasks of which was precisely determining the composition of various natural substances and studying the processes of their mutual transformations. But, with the development of chemistry as a whole, the methods of work used in it were significantly improved, and, along with its purely auxiliary significance as one of the auxiliary departments of chemistry, analytical chemistry now has the significance of a completely independent department of chemical knowledge with very serious and important theoretical tasks. Modern physical chemistry had a very important influence on the development of analytical chemistry, which enriched it with a number of completely new methods of work and theoretical foundations, which include the doctrine of solutions (see), the theory of electrolytic dissociation, the law of mass action (see Chemical equilibrium) and the whole doctrine of chemical affinity.

Methods of analytical chemistry

Comparison of analytical chemistry methods

Totality traditional methods Determining the composition of a substance by its sequential chemical decomposition is called “wet chemistry” (“wet analysis”). These methods have relatively low accuracy, require relatively low qualifications of analysts and are now almost completely replaced by modern ones. instrumental methods(optical, mass spectrometric, electrochemical, chromatographic and other physicochemical methods) determining the composition of a substance. However, wet chemistry has its advantage over spectrometric methods - it allows, through standardized procedures (systematic analysis), to directly determine the composition and different oxidative states of elements such as iron (Fe +2, Fe +3), titanium, etc.

Analytical methods can be divided into gross and local. Bulk methods of analysis usually require a separated, subdivided substance (a representative sample). Local Methods determine the composition of a substance in a small volume in the sample itself, which makes it possible to compile “maps” of the distribution of the chemical properties of the sample over its surface and/or depth. Methods should also be highlighted direct analysis, that is, not related to the preliminary preparation of the sample. Sample preparation is often necessary (eg crushing, pre-concentration or separation). Statistical methods are used when preparing samples, interpreting results, and estimating the number of analyzes.

Methods of qualitative chemical analysis

To determine the qualitative composition of a substance, it is necessary to study its properties, which, from the point of view of analytical chemistry, can be of two types: the properties of the substance as such, and its properties in chemical transformations.

The first include: physical state (solid, liquid, gas), its structure in the solid state (amorphous or crystalline substance), color, smell, taste, etc. In this case, it is often already based on external properties alone, determined with the help of organs human feelings, it seems possible to establish the nature of a given substance. In most cases, it is necessary to transform a given substance into some new one with clearly defined characteristic properties, using for this purpose some specially selected compounds called reagents.

The reactions used in analytical chemistry are extremely diverse and depend on the physical properties and degree of complexity of the composition of the substance being studied. In the case where a obviously pure, homogeneous chemical compound is subject to chemical analysis, the work is done relatively easily and quickly; when you have to deal with a mixture of several chemical compounds, the question of its analysis becomes more complicated, and when doing work you need to adhere to some specific system in order not to overlook a single element included in the substance. There are two types of reactions in analytical chemistry: wet reactions(in solutions) and dry reactions.

Reactions in solutions

In qualitative chemical analysis, only reactions in solutions are used that are easily perceived by human senses, and the moment of occurrence of the reaction is recognized by one of the following phenomena:

1. the formation of a water-insoluble precipitate,
2. change in solution color
3. gas release.

Formation of sediment in reactions of chemical analysis depends on the formation of some water-insoluble substance; if, for example, sulfuric acid or a water-soluble salt is added to a solution of any barium salt, a white powdery precipitate of barium sulfate is formed:

BaCl 2 + H 2 SO 4 = 2HCl + BaSO 4 ↓

Keeping in mind that some other metals can give a similar reaction to the formation of a white precipitate under the influence of sulfuric acid, for example, lead, which can form the insoluble sulfate salt PbSO 4, to be completely sure that this is exactly one or another metal, it is necessary to produce more calibration reactions, subjecting the precipitate formed in the reaction to appropriate research.

To successfully carry out the reaction of precipitation formation, in addition to selecting the appropriate reagent, it is also necessary to observe a number of very important conditions regarding the strength of solutions of the salt and reagent being studied, the proportion of both, temperature, duration of interaction, etc. When considering precipitation formed in chemical reactions analysis, it is necessary to pay attention to their appearance, that is, color, structure (amorphous and crystalline precipitates), etc., as well as their properties in relation to the influence of heat, acids or alkalis, etc. When interacting weak solutions Sometimes it is necessary to wait for the formation of sediment for up to 24-48 hours, provided that they are kept at a certain temperature.

The reaction of precipitate formation, regardless of its qualitative significance in chemical analysis, is often used to separate certain elements from each other. For this purpose, a solution containing compounds of two or more elements is treated with an appropriate reagent capable of converting some of them into insoluble compounds, and then the resulting precipitate is separated from the solution (filtrate) by filtration, further studying them separately. If we take, for example, the salts of potassium chloride and barium chloride and add sulfuric acid to them, an insoluble precipitate of barium sulfate BaSO 4 and water-soluble potassium sulfate K 2 SO 4 are formed, which can be separated by filtration. When separating a precipitate of a water-insoluble substance from a solution, care must first be taken to ensure that it receives an appropriate structure that allows the filtering work to be carried out without difficulty, and then, having collected it on the filter, it is necessary to thoroughly wash it from foreign impurities. According to the research of V. Ostwald, it must be borne in mind that when using a certain amount of water for washing, it is more advisable to rinse the sediment many times in small portions of water than, on the contrary, several times in large portions. As for the success of the separation reaction of any element in the form of an insoluble precipitate, then, based on the theory of solutions, W. Ostwald established that for a sufficiently complete separation of any element in the form of an insoluble precipitate, it is always necessary to take an excess of the reagent used for precipitation .

Change in solution color is one of the very important signs in the reactions of chemical analysis and is very important, especially in connection with the processes of oxidation and reduction, as well as in work with chemical indicators (see below - alkalimetry and acidimetry).

Examples color reactions in qualitative chemical analysis the following can be used: potassium thiocyanate KCNS gives a characteristic blood-red color with iron oxide salts; with ferrous oxide salts the same reagent does not produce anything. If you add any oxidizing agent, for example, chlorine water, to a solution of slightly green ferric chloride FeCl 2, the solution turns yellow due to the formation of ferric chloride, which is the highest oxidation state of this metal. If you take potassium dichromate K 2 Cr 2 O 7 orange in color and add to it in solution a little sulfuric acid and some reducing agent, for example, wine alcohol, the orange color changes to dark green, corresponding to the formation of a lower oxidation state of chromium in the form of a salt chromium sulfate Cr 3 (SO 4) 3.

Depending on the progress of the chemical analysis, it is often necessary to carry out these processes of oxidation and reduction. The most important oxidizing agents are: halogens, nitric acid, hydrogen peroxide, potassium permanganate, potassium dihydroxide; the most important reducing agents are: hydrogen at the time of release, hydrogen sulfide, sulfurous acid, tin chloride, hydrogen iodide.

Gas evolution reactions in solutions during the production of qualitative chemical analysis most often have no independent significance and are auxiliary reactions; most often we encounter the release of carbon dioxide CO 2 - during the action of acids on carbon dioxide salts, hydrogen sulfide - during the decomposition of sulfur metals with acids, etc.

Dry reactions

These reactions are used in chemical analysis, mainly in the so-called. “preliminary testing”, when testing sediments for purity, for verification reactions and when studying minerals. The most important reactions of this kind consist of testing a substance in relation to:

1. its fusibility when heated,
2. ability to color the non-luminous flame of a gas burner,
3. volatility when heated,
4. oxidation and reduction abilities.

To carry out these tests, in most cases, a non-luminous flame of a gas burner is used. The main components of illuminating gas (hydrogen, carbon monoxide, swamp gas and other hydrocarbons) are reducing agents, but when it burns in air (see Combustion), a flame is formed, in various parts of which the conditions necessary for reduction or oxidation can be found, and equals for heating to a more or less high temperature.

Fusibility test It is carried out mainly when studying minerals, for which a very small fragment of them, fixed in a thin platinum wire, is introduced into the part of the flame that has the highest temperature, and then, using a magnifying glass, they observe how the edges of the sample are rounded.

Flame color test is made by introducing a small sepia sample of a small sample of the substance on a platinum wire, first into the base of the flame, and then into the part of it with the highest temperature.

Volatility test is produced by heating a sample of a substance in an assay cylinder or in a glass tube sealed at one end, and volatile substances turn into vapors, which then condense in the colder part.

Oxidation and reduction in dry form can be produced in balls of fused borax ( 2 4 7 + 10 2 ) The substance tested is introduced in small quantities into balls obtained by melting these salts on a platinum wire, and they are then heated in the oxidizing or reducing part of the flame. Restoration can be done in a number of other ways, namely: heating on a stick charred with soda, heating in a glass tube with metals - sodium, potassium or magnesium, heating in charcoal using a blowpipe, or simple heating.

Classification of elements

The classification of elements adopted in analytical chemistry is based on the same division that is accepted in general chemistry - into metals and non-metals (metalloids), the latter being most often considered in the form of the corresponding acids. To carry out a systematic qualitative analysis, each of these classes of elements is divided in turn into groups with some common group characteristics.

Metals in analytical chemistry are divided into two departments, which in turn are divided into five groups:

1. Metals whose sulfur compounds are soluble in water- the distribution of metals in this department into groups is based on the properties of their carbon dioxide salts. 1st group: potassium, sodium, rubidium, cesium, lithium. Sulfur compounds and their carbon dioxide salts are soluble in water. There is no general reagent for the precipitation of all metals of this group in the form of insoluble compounds. 2nd group: barium, strontium, calcium, magnesium. Sulfur compounds are soluble in water, carbon dioxide salts are insoluble. A common reagent that precipitates all metals of this group in the form of insoluble compounds is ammonium carbonate.
2. Metals whose sulfur compounds are insoluble in water- to divide this department into three groups, they use the ratio of their sulfur compounds to weak acids and ammonium sulfide. 3rd group: aluminum, chromium, iron, manganese, zinc, nickel, cobalt.

Aluminum and chromium do not form sulfur compounds by water; other metals form sulfur compounds, which, like their oxides, are soluble in weak acids. Hydrogen sulfide does not precipitate them from an acidic solution; ammonium sulfide precipitates oxides or sulfur compounds. Ammonium sulphide is a common reagent for this group, and an excess of its sulfur compounds does not dissolve. 4th group: silver, lead, bismuth, copper, palladium, rhodium, ruthenium, osmium. Sulfur compounds are insoluble in weak acids and are precipitated by hydrogen sulfide in an acidic solution; they are also insoluble in ammonium sulphide. Hydrogen sulfide is a common reactant for this group. 5th group: tin, arsenic, antimony, gold, platinum. Sulfur compounds are also insoluble in weak acids and are precipitated by hydrogen sulfide from an acidic solution. But they are soluble in ammonium sulphide and form water-soluble sulfasalts with it.

Nonmetals (metalloids) always have to be discovered in chemical analysis in the form of the acids they form or their corresponding salts. The basis for dividing acids into groups is the properties of their barium and silver salts in relation to their solubility in water and partly in acids. Barium chloride is a general reagent for group 1, silver nitrate in nitrate solution is for group 2, barium and silver salts of group 3 acids are soluble in water. 1st group: in a neutral solution, barium chloride precipitates insoluble salts; Silver salts are insoluble in water, but soluble in nitric acid. These include acids: chromic, serous, sulfurous, aqueous, carbonic, silicon, sulfuric, hydrofluorosilicic (barium salts, insoluble in acids), arsenic and arsenic. 2nd group: in a solution acidified with nitric acid, silver nitrate gives a precipitate. These include acids: hydrochloric, hydrobromic and hydroiodic, hydrocyanic, hydrogen sulfide, ferric and ferric hydrocyanide and iodine. 3rd group: nitric acid and perchloric acid, which are not precipitated by either silver nitrate or barium chloride.

However, it must be borne in mind that the reagents indicated for acids are not general reagents that could be used to separate acids into groups. These reagents can only give an indication of the presence of an acidic or other group, and to discover each individual acid one must use the private reactions belonging to them. The above classification of metals and nonmetals (metalloids) for the purposes of analytical chemistry was adopted in Russian schools and laboratories (according to N.A. Menshutkin); in Western European laboratories another classification was adopted, based, however, essentially on the same principles.

Theoretical basis of reactions

The theoretical foundations for reactions of qualitative chemical analysis in solutions must be sought, as already indicated above, in the departments of general and physical chemistry about solutions and chemical affinity. One of the first, most important issues is the state of all minerals in aqueous solutions, in which, according to the theory of electrolytic dissociation, all substances belonging to the classes of salts, acids and alkalis dissociate into ions. Therefore, all reactions of chemical analysis occur not between whole molecules of compounds, but between their ions. For example, the reaction of sodium chloride NaCl and silver nitrate AgNO 3 occurs according to the equation:

Na + + Cl - + Ag + + (NO 3) - = AgCl↓ + Na + + (NO 3) - sodium ion + chlorine ion + silver ion + nitric acid anion = insoluble salt + nitric acid anion

Consequently, silver nitrate is not a reagent for sodium chloride or hydrochloric acid, but only for chlorine ion. Thus, for each salt in solution, from the point of view of analytical chemistry, its cation (metal ion) and anion (acid residue) must be considered separately. For a free acid, hydrogen ions and an anion must be considered; finally, for each alkali - a metal cation and a hydroxyl anion. And essentially the most important task of qualitative chemical analysis is to study the reactions of various ions and how to discover them and separate them from each other.

To achieve the latter goal, by the action of appropriate reagents, ions are converted into insoluble compounds that precipitate from solution in the form of precipitation, or are isolated from solutions in the form of gases. In the same theory of electrolytic dissociation, one must look for an explanation for the action of chemical indicators, which often find application in chemical analysis. According to the theory of W. Ostwald, all chemical indicators are relatively weak acids, partially dissociated in aqueous solutions. Moreover, some of them have colorless whole molecules and colored anions, others, on the contrary, have colored molecules and a colorless anion or an anion of a different color; When exposed to the influence of free hydrogen ions of acids or hydroxyl ions of alkali, chemical indicators can change the degree of their dissociation, and at the same time their color. The most important indicators are:

1. Methyl orange, which in the presence of free hydrogen ions (acidic reaction) gives a pink color, and in the presence of neutral salts or alkalis gives a yellow color;
2. Phenolphthalein - in the presence of hydroxyl ions (alkaline reaction) gives a characteristic red color, and in the presence of neutral salts or acids it is colorless;
3. Litmus turns red under the influence of acids, and turns blue under the influence of alkalis, and finally
4. Curcumin turns brown under the influence of alkalis, and in the presence of acids again takes on a yellow color.

Chemical indicators have very important applications in volumetric chemical analysis (see below). In reactions of qualitative chemical analysis, one often encounters the phenomenon of hydrolysis, that is, the decomposition of salts under the influence of water, and the aqueous solution acquires a more or less strong alkaline or acidic reaction.

Progress of qualitative chemical analysis

In a qualitative chemical analysis, it is important to determine not only what elements or compounds are included in the composition of a given substance, but also in what, approximately, relative quantities these components are found. For this purpose, it is always necessary to proceed from certain quantities of the analyzed substance (usually it is enough to take 0.5-1 grams) and, when performing the analysis, compare the amount of individual precipitation with each other. It is also necessary to use solutions of reagents of a certain strength, namely: normal, half-normal, one tenth of normal.

Every qualitative chemical analysis is divided into three parts:

1. preliminary test,
2. discovery of metals (cations),
3. discovery of non-metals (metalloids) or acids (anions).

Regarding the nature of the analyte, four cases may occur:

1. solid non-metallic substance,
2. solid substance in the form of a metal or metal alloy,
3. liquid (solution),

When analyzing solid non-metallic substance First of all, an external examination and microscopic examination are carried out, as well as a preliminary test using the above methods of analysis in dry form. Initially, a sample of a substance is dissolved, depending on its nature, in one of the following solvents: water, hydrochloric acid, nitric acid and aqua regia (a mixture of hydrochloric and nitric acids). Substances that are unable to dissolve in any of the above solvents are transferred into solution using some special techniques, such as: fusion with soda or potash, boiling with soda solution, heating with certain acids, etc. The resulting solution is subjected to systematic analysis with preliminary isolation of metals and acids into groups and their further separation into individual elements, using their characteristic private reactions.

When analyzing metal alloy a certain sample of it is dissolved in nitric acid (in rare cases in aqua regia), and the resulting solution is evaporated to dryness, after which the solid residue is dissolved in water and subjected to systematic analysis.

If the substance is liquid, first of all, attention is paid to its color, smell and reaction to litmus (acidic, alkaline, neutral). To verify the presence of any solids in the solution, a small portion of the liquid is evaporated on a platinum plate or watch glass. After these preliminary tests, the liquid is apalized using conventional methods.

Analysis gases produced by some special methods indicated in the quantitative analysis.

Methods of quantitative chemical analysis

Quantitative chemical analysis aims to determine the relative amounts of the individual constituents of any chemical compound or mixture. The methods used in it depend on the qualities and composition of the substance, and therefore quantitative chemical analysis must always be preceded by qualitative chemical analysis

To perform quantitative analysis, two different methods can be used: gravimetric and volumetric. With the weight method, the bodies being determined are isolated in the form of, if possible, insoluble or poorly soluble compounds of known chemical composition, and their weight is determined, on the basis of which the amount of the desired element can be found by calculation. In volumetric analysis, the volumes of titrated (containing a certain amount of reagent) solutions used for analysis are measured. In addition, a number of special methods of quantitative chemical analysis differ, namely:

1. electrolytic based on the separation of individual metals by electrolysis,
2. colorimetric, produced by comparing the color intensity of a given solution with the color of a solution of a certain strength,
3. organic analysis, which consists of burning organic matter into carbon dioxide C0 2 and water H 2 0 and determining by the amount of their relative content of carbon and hydrogen in the substance,
4. gas analysis, which consists in determining by some special methods the qualitative and quantitative composition of gases or their mixtures.

Represents a very special group medical chemical analysis, covering a number of different methods for studying blood, urine and other waste products of the human body.

Gravity quantitative chemical analysis

Methods of gravimetric quantitative chemical analysis are of two types: direct analysis method And method of indirect (indirect) analysis. In the first case, the component to be determined is isolated in the form of some insoluble compound, and the weight of the latter is determined. Indirect analysis is based on the fact that two or more substances subjected to the same chemical treatment undergo unequal changes in their weight. Having, for example, a mixture of potassium chloride and sodium nitrate, you can determine the first of them by direct analysis, precipitating the chlorine in the form of silver chloride and weighing it. If there is a mixture of potassium and sodium chloride salts, you can determine their ratio indirectly by precipitating all the chlorine in the form of silver chloride and determining its weight, followed by calculation.

Volumetric chemical analysis

Electrolysis Analysis

Colorimetric methods

Elemental organic analysis

Gas analysis

Classification of analytical chemistry methods

• Elemental analysis methods
  • X-ray spectral analysis (X-ray fluorescence)
  • Neutron activation analysis ( English) (see radioactivation analysis)
  • Auger electron spectrometry (EOS) ( English); see Auger effect
  • Analytical atomic spectrometry is a set of methods based on the transformation of analyzed samples into the state of individual free atoms, the concentrations of which are then measured spectroscopically (sometimes X-ray fluorescence analysis is also included here, although it is not based on sample atomization and is not associated with atomic vapor spectroscopy).
    • MS - mass spectrometry with registration of masses of atomic ions
      • ICP-MS - inductively coupled plasma mass spectrometry (see inductively coupled plasma in mass spectrometry)
      • LA-ICP-MS - mass spectrometry with inductively coupled plasma and laser ablation
      • LIMS - laser spark mass spectrometry; see laser ablation (commercial example: LAMAS-10M)
      • MSVI - Secondary Ion Mass Spectrometry (SIMS)
      • TIMS - thermal ionization mass spectrometry (TIMS)
      • High-energy particle accelerator mass spectrometry (AMS)
    • AAS - atomic absorption spectrometry
      • ETA-AAS - atomic absorption spectrometry with electrothermal atomization (see atomic absorption spectrometers)
      • SVZR - cavity decay time spectroscopy (CRDS)
      • VRLS - intracavity laser spectroscopy
    • AES - atomic emission spectrometry
      • spark and arc as sources of radiation (see spark discharge; electric arc)
      • ICP-AES - inductively coupled plasma atomic emission spectrometry
      • LIES - laser spark emission spectrometry (LIBS or LIPS); see laser ablation
    • AFS - atomic fluorescence spectrometry (see fluorescence)
      • ICP-AFS - atomic fluorescence spectrometry with inductively coupled plasma (Baird devices)
      • LAFS - laser atomic fluorescence spectrometry
      • APS on hollow cathode lamps (commercial example: AI3300)
    • AIS - atomic ionization spectrometry
      • LAIS (LIIS) - laser atomic ionization or laser-intensified ionization spectroscopy (eng. Laser Enhanced Ionization, LEI )
      • RIMS - laser resonance ionization mass spectrometry
      • OG - optogalvanics (LOGS - laser optogalvanic spectroscopy)

• Other analysis methods
  • titrimetry, volumetric analysis
  • gravimetric analysis - gravimetry, electrogravimetry
  • spectrophotometry (usually absorption) of molecular gases and condensed matter
    • electron spectrometry (visible spectrum and UV spectrometry); see electron spectroscopy
    • vibrational spectrometry (IR spectrometry); see vibrational spectroscopy
  • Raman spectroscopy; see Raman effect
  • luminescence analysis
  • mass spectrometry with registration of masses of molecular and cluster ions, radicals
  • ion mobility spectrometry (

Depending on the task at hand, there are 3 groups of analytical chemistry methods:

• 1) detection methods allow you to determine which elements or substances (analytes) are present in the sample. They are used to conduct qualitative analysis;
• 2) determination methods make it possible to establish the quantitative content of analytes in a sample and are used to carry out quantitative analysis;
• 3) separation methods allow you to isolate the analyte and separate interfering components. They are used in qualitative and quantitative analysis. There are various methods of quantitative analysis: chemical, physicochemical, physical, etc.

Chemical methods are based on the use of chemical reactions (neutralization, oxidation-reduction, complexation and precipitation) into which the analyte enters. A qualitative analytical signal in this case is the visual external effect of the reaction - a change in the color of the solution, the formation or dissolution of a precipitate, the release of a gaseous product. In quantitative determinations, the volume of the released gaseous product, the mass of the formed precipitate, and the volume of a reagent solution with a precisely known concentration spent on interaction with the substance being determined are used as an analytical signal.

Physical methods do not use chemical reactions, but measure any physical properties (optical, electrical, magnetic, thermal, etc.) of the analyzed substance, which are a function of its composition.

Physicochemical methods use changes in the physical properties of the analyzed system as a result of chemical reactions. Physicochemical methods also include chromatographic methods of analysis, based on the processes of sorption-desorption of a substance on a solid or liquid sorbent under dynamic conditions, and electrochemical methods (potentiometry, voltammetry, conductometry).

Physical and physicochemical methods are often combined under the general name instrumental methods of analysis, since analytical instruments and devices that record physical properties or their changes are used to carry out the analysis. When conducting a quantitative analysis, the analytical signal is measured - a physical quantity associated with the quantitative composition of the sample. If quantitative analysis is carried out using chemical methods, then the basis of the determination is always a chemical reaction.

There are 3 groups of quantitative analysis methods:

• - Gas analysis
• - Titrimetric analysis
• - Gravimetric analysis

The most important among chemical methods of quantitative analysis are gravimetric and titrimetric methods, which are called classical methods of analysis. These methods are standard for assessing the accuracy of a determination. Their main area of ​​application is the precision determination of large and medium quantities of substances.

Classical methods of analysis are widely used at chemical industry enterprises to monitor the progress of the technological process, the quality of raw materials and finished products, and industrial waste. On the basis of these methods, pharmaceutical analysis is carried out - determining the quality of drugs and medicines that are produced by chemical and pharmaceutical enterprises.

4.2. CHROMATOGRAPHIC METHODS

4.3. CHEMICAL METHODS

4.4. ELECTROCHEMICAL METHODS

4.5. SPECTROSCOPIC METHODS

4.6. MASS SPECTROMETRIC METHODS

4.7. ANALYSIS METHODS BASED ON RADIOACTIVITY

4.8. THERMAL METHODS

4.9. BIOLOGICAL ANALYSIS METHODS

5. CONCLUSION

6. LIST OF REFERENCES USED

INTRODUCTION

Chemical analysis serves as a means of monitoring production and product quality in a number of sectors of the national economy. Mineral exploration is based to varying degrees on the results of analysis. Analysis is the main means of monitoring environmental pollution. Determining the chemical composition of soils, fertilizers, feed and agricultural products is important for the normal functioning of the agro-industrial complex. Chemical analysis is indispensable in medical diagnostics and biotechnology. The development of many sciences depends on the level of chemical analysis and the laboratory’s equipment with methods, instruments and reagents.

The scientific basis of chemical analysis is analytical chemistry, a science that has been a part, and sometimes the main part, of chemistry for centuries.

Analytical chemistry is the science of determining the chemical composition of substances and, partly, their chemical structure. Analytical chemistry methods make it possible to answer questions about what a substance consists of and what components are included in its composition. These methods often make it possible to find out in what form a given component is present in a substance, for example, to determine the oxidation state of an element. It is sometimes possible to estimate the spatial arrangement of components.

When developing methods, you often have to borrow ideas from related fields of science and adapt them to your goals. The task of analytical chemistry includes developing the theoretical foundations of methods, establishing the limits of their applicability, assessing metrological and other characteristics, and creating methods for analyzing various objects.

Methods and means of analysis are constantly changing: new approaches are involved, new principles and phenomena are used, often from distant fields of knowledge.

The method of analysis is understood as a fairly universal and theoretically justified method for determining the composition, regardless of the component being determined and the object being analyzed. When they talk about a method of analysis, they mean the underlying principle, a quantitative expression of the relationship between the composition and any measured property; selected implementation techniques, including identification and elimination of interference; devices for practical implementation and methods for processing measurement results. An analysis technique is a detailed description of the analysis of a given object using the selected method.

Three functions of analytical chemistry as a field of knowledge can be distinguished:

1. solving general questions of analysis,

2. development of analytical methods,

3. solving specific analysis problems.

You can also highlight qualitative And quantitative tests. The first solves the question of which components the analyzed object includes, the second provides information about the quantitative content of all or individual components.

2. CLASSIFICATION OF METHODS

All existing methods of analytical chemistry can be divided into methods of sampling, sample decomposition, separation of components, detection (identification) and determination. There are hybrid methods that combine separation and determination. Detection and definition methods have much in common.

Determination methods are of greatest importance. They can be classified according to the nature of the property being measured or the method of recording the corresponding signal. Determination methods are divided into chemical , physical And biological. Chemical methods are based on chemical (including electrochemical) reactions. This also includes methods called physicochemical. Physical methods are based on physical phenomena and processes, biological methods are based on the phenomenon of life.

The main requirements for analytical chemistry methods are: accuracy and good reproducibility of results, low detection limit of the required components, selectivity, rapidity, ease of analysis, and the possibility of its automation.

When choosing an analysis method, you need to clearly know the purpose of the analysis, the tasks that need to be solved, and evaluate the advantages and disadvantages of the available analysis methods.

3. ANALYTICAL SIGNAL

After sampling and preparation of the sample, the stage of chemical analysis begins, at which the component is detected or its quantity is determined. For this purpose, they measure analytical signal. In most methods, the analytical signal is the average of measurements of a physical quantity at the final stage of analysis, functionally related to the content of the component being determined.

If it is necessary to detect any component, it is usually fixed appearance analytical signal - the appearance of a precipitate, color, line in the spectrum, etc. The appearance of an analytical signal must be reliably recorded. When determining the amount of a component, it is measured magnitude analytical signal - sediment mass, current strength, spectrum line intensity, etc.

4. METHODS OF ANALYTICAL CHEMISTRY

4.1. METHODS OF MASKING, SEPARATION AND CONCENTRATION

Masking.

Masking is the inhibition or complete suppression of a chemical reaction in the presence of substances that can change its direction or speed. In this case, no new phase is formed. There are two types of masking: thermodynamic (equilibrium) and kinetic (nonequilibrium). With thermodynamic masking, conditions are created under which the conditional reaction constant is reduced to such an extent that the reaction proceeds insignificantly. The concentration of the masked component becomes insufficient to reliably record the analytical signal. Kinetic masking is based on increasing the difference between the rates of reaction of the masked and analyte substances with the same reagent.

Separation and concentration.

The need for separation and concentration may be due to the following factors: the sample contains components that interfere with the determination; the concentration of the component being determined is below the detection limit of the method; the components being determined are unevenly distributed in the sample; there are no standard samples for calibration of instruments; the sample is highly toxic, radioactive and expensive.

Separation is an operation (process) as a result of which the components that make up the initial mixture are separated from one another.

Concentration is an operation (process) that results in an increase in the ratio of the concentration or amount of microcomponents to the concentration or amount of macrocomponents.

Precipitation and coprecipitation.

Precipitation is typically used to separate inorganic substances. Precipitation of microcomponents with organic reagents, and especially their coprecipitation, provides a high concentration coefficient. These methods are used in combination with determination methods that are designed to obtain an analytical signal from solid samples.

Separation by precipitation is based on the different solubilities of compounds, mainly in aqueous solutions.

Co-precipitation is the distribution of a microcomponent between a solution and a sediment.

Extraction.

Extraction is a physicochemical process of distributing a substance between two phases, most often between two immiscible liquids. It is also a process of mass transfer with chemical reactions.

Extraction methods are suitable for concentration, extraction of microcomponents or macrocomponents, individual and group isolation of components in the analysis of a variety of industrial and natural objects. The method is simple and fast to perform, provides high separation and concentration efficiency, and is compatible with various determination methods. Extraction allows you to study the state of substances in solution under various conditions and determine physicochemical characteristics.

Sorption.

Sorption is well used for separating and concentrating substances. Sorption methods usually provide good separation selectivity and high concentration coefficients.

Sorption– the process of absorption of gases, vapors and dissolved substances by solid or liquid absorbers on a solid carrier (sorbents).

Electrolytic separation and cementation.

The most common method is electrolysis, in which the separated or concentrated substance is isolated on solid electrodes in an elemental state or in the form of some kind of compound. Electrolytic separation (electrolysis) based on the deposition of a substance by electric current at a controlled potential. The most common option is cathodic deposition of metals. The electrode material can be carbon, platinum, silver, copper, tungsten, etc.

Electrophoresis is based on differences in the speeds of movement of particles of different charges, shapes and sizes in an electric field. The speed of movement depends on the charge, field strength and radius of the particles. There are two options for electrophoresis: frontal (simple) and zone (on a carrier). In the first case, a small volume of solution containing the components to be separated is placed in a tube with an electrolyte solution. In the second case, movement occurs in a stabilizing environment, which holds the particles in place after the electric field is turned off.

Method cementation consists in the reduction of components (usually small quantities) on metals with sufficiently negative potentials or almagams of electronegative metals. During cementation, two processes occur simultaneously: cathodic (component release) and anodic (dissolution of the cementing metal).