Qualitative the analysis is intended for the qualitative discovery of individual chemical elements, ions and functional groups. The presence in the analyzed mixture of individual substances, elements, ions and functional groups is usually detected using chemical qualitative reactions or on the basis of some physical properties of substances - spectra in the visible and ultraviolet regions of light, radioactive radiation, ability to to adsorption.

Quantitative analysis is carried out in various ways. Chemical methods are widespread, in which the amount of a substance is determined by the amount of reagent used for analysis, by the amount of sediment, etc. Often, for the quantitative determination of substances, their physical properties are used - the magnitude of the refractive angle of solutions of substances, the color intensity, the magnitude of the electric current flowing through solution.

ANALYSIS METHODS

The analysis can be carried out by chemical, instrumental (physical and physico-chemical) methods.

Chemical methods of analysis involve the chemical interaction of substances. The results of a chemical reaction between a substance and a reagent are important here. Chemical methods of analysis are widely used for qualitative analysis, since the nature of the precipitate, the change in color of the solution, the formation of a certain gas can determine which substance is present in the solution.

In quantitative chemical analysis, the resulting precipitate is weighed, the reagent solution is added until the color of the solution or other physical characteristics of the substance change, and the amount of the substance is determined by the amount of the reagent used for analysis.

Instrumental (physical, physico-chemical) methods of analysis use the physical properties of substances. Qualitative analysis when using physical methods is carried out by changing the color of the flame that occurs when a substance is introduced into it, by the absorption and emission spectra of the substance, by the melting point, boiling point and other properties that are characteristic of substances. Quantitative analysis by physical methods is carried out by observing changes in the physical properties of a substance with a change in its quantity. Usually, the intensity of color, the angle of refraction of the solution, the magnitude of the electric current passing through the solution depend on the amount of the substance, and this dependence can be used to determine the amount of the substance.

Physico-chemical methods of analysis combine physical and chemical methods. When carrying out physical and chemical methods, the result of a chemical reaction is observed by changes in the physical properties of a substance or its solution. Physicochemical methods have become widespread and are being intensively developed.

The analysis of a substance can be carried out in order to establish its qualitative or quantitative composition. Accordingly, a distinction is made between qualitative and quantitative analysis.

Qualitative analysis allows you to establish what chemical elements the analyzed substance consists of and what ions, groups of atoms or molecules are included in its composition. When studying the composition of an unknown substance, a qualitative analysis always precedes a quantitative one, since the choice of a method for the quantitative determination of the constituent parts of the analyzed substance depends on the data obtained during its qualitative analysis.

Qualitative chemical analysis is mostly based on the transformation of the analyte into some new compound with characteristic properties: color, a certain physical state, crystalline or amorphous structure, a specific smell, etc. The chemical transformation that occurs in this case is called a qualitative analytical reaction , and the substances that cause this transformation are called reagents (reagents).

For example, to discover Fe +++ ions in a solution, the analyzed solution is first acidified with hydrochloric acid, and then a solution of potassium hexacyanoferrate (II) K4 is added. In the presence of Fe +++, a blue precipitate of iron hexacyanoferrate (II) Fe43 precipitates. (Prussian blue):

Another example of a qualitative chemical analysis is the detection of ammonium salts by heating the analyte with an aqueous solution of sodium hydroxide. Ammonium ions in the presence of OH- ions form ammonia, which is recognized by the smell or by the blue color of wet red litmus paper:

In the examples given, solutions of potassium hexacyanoferrate (II) and sodium hydroxide are, respectively, reagents for Fe+++ and NH4+ ions.

When analyzing a mixture of several substances with similar chemical properties, they are first separated and only then characteristic reactions are carried out for individual substances (or ions), therefore, qualitative analysis covers not only individual reactions for detecting ions, but also methods for their separation.

Quantitative analysis allows you to establish the quantitative ratio of the constituent parts of a given compound or mixture of substances. Unlike qualitative analysis, quantitative analysis makes it possible to determine the content of individual components of the analyte or the total content of the analyte in the test product.

Methods of qualitative and quantitative analysis that allow determining the content of individual elements in the analyzed substance are called elemental analysis; functional groups -- functional analysis; individual chemical compounds characterized by a certain molecular weight - molecular analysis.

A set of various chemical, physical and physicochemical methods for separating and determining individual structural (phase) components of heterogeneous! systems that differ in properties and physical structure and are limited from each other by interfaces are called phase analysis.

task qualitative chromatographic analysis is the interpretation of chromatograms or, in other words, the identification of peaks in a chromatogram. To do this, use the following methods.

Substance addition method is based on the sequential introduction of substances into the analyzed mixture, the presence of which is supposed to be in it. If after that one of the peaks in the chromatogram increases (the retention time coincides), then the peak of the analyzed mixture can be identified with the introduced compound. However, this condition is only necessary, but not sufficient for identification: several substances can have the same (or very close) retention time, and not one. For the reliability of the analysis, such studies are carried out using columns with stationary phases of different nature (polar and non-polar).

Comparison method with tabular data involves determining the qualitative composition of the analyzed mixture by comparing the experimentally determined relative retention volumes of substances (under normal analysis conditions with respect to standard substances) with similar tabular values. To improve the reliability of chromatographic identification, the analysis is carried out using data obtained with phases that are different in nature.

Calculation Methods and Correlation Relations are used in cases where there is no data for the studied compounds in the tables of relative retention volumes. Correlations are used between the logarithm of the retention values ​​and the properties of the analyzed compounds (for example, the number of carbon atoms, boiling point, etc.). So, for example, for the values ​​of retained volumes of alkanes, the following equation is valid:

where Г,у is the increment of the logarithm of the retention value corresponding to a certain combination of bonds (structural element); n,j- the number of structural elements of the type ij in the compound molecule. Obtained in this way V R compared with experimental values: if they are close, there is reason to believe that the identified peak corresponds to the intended connection.

Also used identification by Kovacs indices. As a result of the experiments, it was found that within the same homologous series of various classes of organic compounds (alkanes, alcohols, aldehydes, etc.) in the coordinates:

where P- the number of carbon atoms in the homologue, linear dependencies are obtained (Fig. 5.12).

These dependencies can be used for qualitative analysis of various derivatives of hydrocarbons. Thus, E. Kovacs proposed to characterize retention by the number of carbon atoms (multiplied by 100) that an n-alkane has, so that its retained volume coincides with the retained volume of the substance under study.

Rice. 5.12.

Y - line for n-alkanes;2 - line for homologues

The number of carbon atoms of an n-alkane (usually a fractional value multiplied by 100) is called Kovacs index of this substance J. The Kovacs indices for various stationary phases are well reproducible and tabulated.

the value J any connection for a given stationary phase can be determined graphically, as shown in Fig. 5.12. For this purpose, on the selected stationary phase, the dependence is obtained gV R from P for a number of n-alkanes (pentane, hexane, heptane, etc.).

The data obtained are plotted on a graph lgK fl from their 100. Next, measure UK of all substances of the mixture under study and determine them according to the schedule J, in fig. 5.12 Kovacs index Ud-equal to 598.

For members of any homologous series of alkane derivatives (carboxylic acids, aldehydes, etc.), one can obtain a linear dependence similar to that for alkanes (line 2 in fig. 5.12). The horizontal shift of these two lines relative to each other contributes to the Kovacs index of a functional group (carboxylic, carbonyl, etc.) or a multiple bond. This contribution is called homomorphic factor, its value for many compounds is determined and tabulated

The sum of these homomorphic factors, added to the number n c x 100 base alkane, makes it possible to calculate the Kovacs index for the alleged compound (according to) scientific sources and compare it with the experimental value. The proximity of these values ​​allows us to conclude that the peak on the chromatogram corresponds to the expected substance.

An important step in chromatographic analysis is quantitative interpretation of chromatograms, as a result of which the content of components in the analyzed mixture is determined. The accuracy of the results obtained depends on a number of factors, in particular, on the chosen method of analysis, the characteristics of the detector used, the method of calibration and calculation, and the nature of the analyzed components.

The amount of substance in the chromatographic zone is proportional to the area of ​​the chromatographic peak in the chromatogram. There are several methods for determining the area of ​​chromatographic peaks based on the assumption that the shape of the peak corresponds to a Gaussian curve. Most often, it is defined as the product of the height of the peak and its width at half height: see formula (5.8). Chromatographs of the latest generations are controlled by a computer; in this case, the peak area is calculated by software and displayed on the monitor screen.

The area of ​​the peak on the chromatogram depends not only on the amount of substance in the chromatographic zone, but is also determined by the characteristics of the detector and the conditions of the analysis. So, for different substances, even at their equal concentration in the analyzed mixture, peaks of unequal area are obtained on the chromatogram. Therefore, for quantitative analysis, it is not enough just to determine the area of ​​chromatographic peaks. There is a need to establish for each sample substance the coefficient of proportionality between the peak area and its content (concentration) in the analyzed mixture. In other words, the detector should be calibrated under the chosen analysis conditions. The following calibration methods are commonly used.

Absolute calibration method experimentally determine for each component of the analyzed mixture the dependence of the area of ​​the chromatographic peak on its absolute amount in the sample. This dependence is usually presented in the form of a graph or an empirical equation. Detector sensitivity can change over time, so the absolute calibration needs to be checked and adjusted periodically. When recalibrating, you can limit yourself to checking a few points on the calibration curve.

Internal standard method a substance (internal standard) with a known concentration of Cs t is introduced into the analyzed mixture. Beforehand, for each substance of the mixture, a calibration graph (or equation) is obtained that relates SfJSct with Sv/Co, where S B and 5 St - the area of ​​the peaks of the analyte and internal standard, Sv - the concentration of the analyte in the calibration mixture. During the study, the areas of the peaks of the analyzed substances and the internal standard are determined on the chromatogram, their ratio is calculated, and Sv / Q is found from the calibration graph; t. Further, according to the known Сс t, unknown concentrations of substances Sv-

The use of the internal standard method makes it possible to significantly increase the accuracy of measurements and makes periodic correction of the calibration curve unnecessary. Indeed, a change in the experimental conditions equally affects the change in the parameters of the chromatogram of the standard substance and the components of the sample.

Another advantage of the method is that it is no longer necessary to maintain the exact volume of sample fed to the column. In this case, it is also optional to separate all the peaks in the chromatogram: it is enough that the peaks of the substances of interest and the standard come out separately.

To improve the accuracy of the analysis, it is desirable that the substance used as a standard be close to the components to be determined in terms of retention and content in the analyzed mixture.

Also used calibration with correction factors. Peak area / "th component S, on the chromatogram is proportional to its amount d, in the mixture introduced into the column:

Here to,- correction factor of the substance. In the event that all substances of the analyzed mixture give separate (separated) peaks on the chromatogram, it is possible to calculate the fraction of the / "-th component by the method of internal normalization:

then summation is performed over all peaks. If the numerator and denominator of the right side of the equation are divided by the correction factor of any substance taken as a standard (? st), then we get the equation:

where k, tn \u003d k, / k„ - relative correction factor. It is easy to determine it experimentally by making mixtures of a certain composition of each substance paired with a standard one, or a mixture of all substances of a known composition, including a standard substance. After obtaining chromatograms with such a composition of substances and determining the peak areas of all components, one can find R: ota for all substances from the ratio:

where qjqci- corresponds to the ratio of the amounts of the i-th component and the standard in the initial mixture. Quantities q may be determined by mass (g) or by quantity (mol), from which mass or molar relative correction factors are calculated respectively. Accordingly, mass fractions are determined with mass coefficients, and molar fractions of substances in the mixture are determined with molar coefficients.

Qualitative (non-formalized) methods of analysis are based on the description of analytical procedures at the logical level, and not on strict analytical dependencies. These include methods: expert assessments, scenarios, morphological, comparison of systems of indicators, etc. The application of these methods is characterized by a certain subjectivity, since the intuition, experience and knowledge of the analyst are of great importance.

Expert assessments are quantitative or ordinal assessments of processes or phenomena that cannot be directly measured. They are based on the judgments of experts and therefore cannot be considered completely objective. Scientific methods are being developed to process individual expert assessments in such a way that they give more or less objective answers in the aggregate (using thoughtful forms of questions and answers, which are subsequently processed by a computer).

Scenario - a description of possible options for the development of the object under study under various combinations of certain conditions (selected in advance) for the purpose of further analysis and selection of the most realistic one.

Morphological analysis is used to predict complex processes. This is an expert method of a systematic review of all possible combinations of development of individual elements of the system under study. It is based on complete and rigorous classifications of objects, phenomena, properties and parameters of the system, which make it possible to build and evaluate possible scenarios for its development as a whole.

Quantitative (formalized) methods of analysis are based on fairly strict formalized analytical dependencies. Let's list them:

Classical methods of analysis - the method of chain substitutions, balance sheet, percentage numbers, differential, integral, discounting, etc.;

Methods of economic statistics - average and relative values, grouping, graphical, index, elementary methods for processing time series;

Mathematical and statistical methods for studying relationships - correlation analysis, regression analysis, analysis of variance, factorial analysis, principal components method, analysis of covariance, etc.;

Econometric methods - matrix methods, harmonic analysis, spectral analysis, methods of the theory of production functions, methods of the theory of input-output balance;

Methods of economic cybernetics and optimal programming - methods of system analysis, linear programming, non-linear programming, dynamic programming, etc.;

Methods of operations research and decision theory - methods of graph theory, game theory, tree method, Bayesian analysis, queuing theory, network planning and management methods.

Mathematical methods make it possible to replace approximate calculations with exact calculations, to carry out multivariate comparative analysis, which is practically impossible manually.

3. Methods of financial analysis: horizontal, vertical and trend analysis

Horizontal analysis method- used to assess changes in indicators in dynamics. To determine the absolute change in the indicator, a value is calculated equal to:

∆З = З 1 - З 0,

where Z 1 - the value of the indicator in the reporting period;

З 0 - the value of the indicator in the base period.

To assess the growth rate of the indicator, the value is calculated:

T p (Z) \u003d Z 1: Z 0.

The value of the indicator shows how many times the value of the indicator has changed in the reporting period compared to the base period.

To assess the relative change, the growth rate is calculated using the formula:

T pr (Z) \u003d (Z 1: Z 0 - 1) x 100% \u003d ∆Z: Z 0 x 100%.

The growth rate of T pr (Z) shows how many percent the value of the indicator has changed in the reporting period compared to the base period.

Vertical analysis method- used to analyze complex economic indicators, allows you to determine the share of each component of a complex indicator in the total population.

To evaluate the structure, the formula is used:

where Di is the share of the i-th component;

Zi - absolute value of the i-th component included in the complex indicator;

Z - the value of this complex indicator.

To assess the dynamics of the structure of a complex economic indicator, a horizontal method is used, on the basis of which the absolute and relative changes in each component are determined:

∆Di \u003d Di 1 - Di 0; T pr (Di) \u003d ∆Di: Di ​​0 x 100%.

Vertical analysis of the book value of the organization allows you to determine the quality of the use of a particular type of resource in economic activity, to conduct a comparative analysis of the organization, taking into account industry specifics and other characteristics. Relative indicators of the Di type, in contrast to absolute ones, are more convenient when analyzing the activities of an organization in terms of inflation, and allow an objective assessment of changes in components in dynamics.

Trend analysis method- based on the use of data series of the dynamics of the studied factors, for example, the balance sheet, the structure of assets and liabilities of the organization. Using this method allows you to evaluate the main directions of the organization's development both at the current moment and in subsequent periods.

For each main indicator characterizing the organization's activities, an analysis is made of changes in growth rates, average growth rates for the periods under consideration (month, quarter, half year, year), and the main directions of change in these indicators are identified. The results of calculating the average values ​​of the growth rate (growth rate), taking into account the links between the main indicators, allow us to calculate the forecast value of the indicator under study for the future. A forecast based on trend models allows, with a certain degree of reliability, to calculate the value of the predicted factor, choose the most rational management decisions and evaluate the consequences of these decisions for the financial and economic activities of the organization.

MOSCOW AUTOMOTIVE AND ROAD INSTITUTE (STATE TECHNICAL UNIVERSITY)

Department of Chemistry

I approve the head. department professor

I.M. Papisov "___" ____________ 2007

A.A. LITMANOVICH, O.E. LITMANOVYCH

ANALYTICAL CHEMISTRY Part 1: Qualitative Chemical Analysis

Toolkit

for students of the second year of the specialty "Engineering environmental protection"

MOSCOW 2007

Litmanovich A.A., Litmanovich O.E. Analytical Chemistry: Part 1: Qualitative Chemical Analysis: Methodological Guide / MADI

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

The basic chemical laws of the 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 "Environmental Engineering".

© Moscow Automobile and Road Institute (State Technical University), 2008

CHAPTER 1. SUBJECT AND OBJECTIVES 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. With the help of these methods, it is established which chemical elements, in what form and in what quantity are contained in the object under study. In analytical chemistry, two large sections are distinguished - qualitative and quantitative analysis. The tasks set by analytical chemistry are solved with the help of chemical and instrumental methods (physical, physicochemical).

In chemical methods of analysis the element to be determined is converted into a compound having such properties, with the help of which it is possible to establish the presence of this element or to measure its amount. One of the main ways to measure the amount of a formed compound is to determine the mass of a substance by weighing on an analytical balance - a gravimetric method of analysis. Methods of quantitative chemical analysis and instrumental methods of analysis will be discussed in Part 2 of the Methodological Guide to Analytical Chemistry.

An urgent direction in the development of modern analytical chemistry is the development of methods for analyzing environmental objects, waste and waste water, gas emissions from industrial enterprises and road transport. Analytical control makes it possible to detect the excess content of especially 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 foundations of chemical analysis include: knowledge of the properties of aqueous solutions; acid-base equilibria in aqueous

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

1.2. analytical reactions. Conditions and methods for their implementation

Qualitative chemical analysis is carried out using analytical reactions, accompanied by noticeable external changes: for example, gas evolution, discoloration, 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 value of the detection limit (Cmin) - the lowest concentration of the component in the solution sample, at which this analysis technique 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 the 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 this ion in the presence of other ions. As examples of specific reactions(of which there are few) are as follows.

a) The interaction of ammonium salts with an excess of alkali when heated:

NH4Cl + NaOH → NH3 + NaCl + H2O . (one)

The released ammonia is easy to recognize by its characteristic odor (“ammonia”) or by a change in the color of a 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) The interaction of ferrous salts with potassium hexacyanoferrate (III) K3 with the formation of a blue precipitate (Turnbull 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 in that the presence of unknown ions can be determined by the 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 the achievement of thermodynamic equilibrium in the system in a short time (practically with the rate of mixing of components in reactions in solution).

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

dissociation for weak electrolytes and solubility products (PR) for sparingly soluble salts, bases

These factors determine the depth of the reaction, the yield of the product and the accuracy of the determination of the analyte (or the very possibility of detecting a certain 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 much lower than in an aqueous solution (the SP value is lower), 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 the analysis of the solution.

In qualitative chemical analysis, a rational sequence is developed in the separation and detection of ions - a systematic course (scheme) of analysis. In this case, ions are isolated from the mixture in groups, based on their equal relation 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 precipitation and solutions, in which individual ions are then detected . The use of group reagents makes it possible to decompose the complex problem of qualitative analysis into a number of simpler ones. The ratio of ions to the action of certain

group reagents is the basis analytical classification of ions.

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

The presence of a color in a clear 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 H2O molecules as ligands, for which the color of the solution is indicated in Table. one .

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

pH measurement 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
ny pH water-
solution
	Hydrolysis			Na+ , K+ , Ba2+ ,		SO3 2- , S2- , CO3 2- ,
	educated			Ca2+		CH3COO-
				metals s-		(corresponding
	basis			electronic		acids are 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 to the sample solution or

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

Table 3

solution pH			Corresponding ion
after adding
			in solution
	Ammonia		NH4+
	(smell of ammonia)
		unpleasant	SO3 2-
	smell (SO2)
	"Vinegar"	(acetic	CH3COO-
	acid CH3COOH)
	(hydrogen sulfide H2S)

The reason for the smell (see Table 3) is the well-known property of reactions in electrolyte solutions - the 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 by 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. The classification of cations is carried out according to the following criteria:

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

c) the ability to form stable complex compounds with ammonia (NH3) - ammoniates (i.e. amino 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 action
			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–
	NH4 OH (conc.)	Fe2+ ​​, Fe3+ , Mg2+ ,	Precipitate: Fe(OH)2,
		Mn2+	Fe(OH)3 , Mg(OH)2 ,
			Mn(OH)2
	NH4 OH (conc.)	Cu2+ , Ni2+ , Co2+	Mortar (painted):
			2+ , blue
			2+ , blue
			2+ , yellow (on
			the air turns blue due to
			oxidation to Co3+ )
	Missing	NH4 + , Na+ , K+

Obviously, the above 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 analytic groups.

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

2.2.1. First group (Ag+ , Pb2+ )

Test solution containing Ag+, Pb2+ cations

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

If PC > PR, are formed 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)

Obviously, at low concentrations of precipitated cations, the concentration of Cl– anions should be relatively high

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

Partially goes into solution	In the sediment - 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 sediment:	complexation:
1. With KI reagent (after	AgCl↓+ 2NH4 OH(e) →
cooling):	→+ +Cl– +2H2O
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 precipitate of a mixture of chlorides + 30%