Qualitative chemical analysis. Chemical methods of qualitative analysis

. Purpose, possible methods. Qualitative chemical analysis of inorganic and organic substances

Qualitative analysis has its own purpose detection of certain substances or their components in the analyzed object. Detection is carried out by identification substances, that is, establishing the identity (sameness) of the AS of the analyzed object and the known AS of the determined substances under the conditions of the applied method of analysis. To do this, this method preliminarily examines reference substances (Section 2.1), in which the presence of the substances to be determined is known. For example, it was found that the presence of a spectral line with a wavelength of 350.11 nm in the emission spectrum of the alloy, when the spectrum is excited by an electric arc, indicates the presence of barium in the alloy; the blueness of an aqueous solution when starch is added to it is an AC for the presence of I 2 in it and vice versa.

Qualitative analysis always precedes quantitative.

At present, qualitative analysis is performed by instrumental methods: spectral, chromatographic, electrochemical, etc. Chemical methods are used at certain instrumental stages (sample opening, separation and concentration, etc.), but sometimes using chemical analysis, you can get results more simply and quickly, for example, to establish the presence of double and triple bonds in unsaturated hydrocarbons by passing them through bromine water or an aqueous solution of KMnO 4 . In this case, the solutions lose their color.

A detailed qualitative chemical analysis makes it possible to determine the elemental (atomic), ionic, molecular (material), functional, structural and phase compositions of inorganic and organic substances.

In the analysis of inorganic substances, elemental and ionic analyzes are of primary importance, since knowledge of the elemental and ionic composition is sufficient to establish the material composition of inorganic substances. The properties of organic substances are determined by their elemental composition, but also by their structure, the presence of various functional groups. Therefore, the analysis of organic substances has its own specifics.

Qualitative chemical analysis is based on a system of chemical reactions characteristic of a given substance - separation, separation and detection.

The following requirements apply to chemical reactions in qualitative analysis.

1. The reaction should proceed almost instantly.

2. The reaction must be irreversible.

3. The reaction must be accompanied by an external effect (AS):

a) a change in the color of the solution;

b) the formation or dissolution of a precipitate;

c) release of gaseous substances;

d) flame coloring, etc.

4. The reaction should be sensitive and, if possible, specific.

Reactions that make it possible to obtain an external effect with an analyte are called analytical , and the substance added for this - reagent . Analytical reactions carried out between solids are referred to as " dry way ", and in solutions -" wet way ».

The “dry route” reactions include reactions carried out by grinding a solid test substance with a solid reagent, as well as by obtaining colored glasses (pearls) by fusing certain elements with borax.

Much more often, the analysis is carried out "wet way", for which the analyte is transferred into solution. Reactions with solutions can be performed test tube, drip and microcrystalline methods. In test-tube semi-microanalysis, it is performed in test tubes with a capacity of 2-5 cm 3 . To separate the precipitates, centrifugation is used, and evaporation is carried out in porcelain cups or crucibles. Drop analysis (N.A. Tananaev, 1920) is carried out on porcelain plates or strips of filtered paper, obtaining color reactions by adding one drop of a reagent solution to one drop of a solution of a substance. Microcrystalline analysis is based on the detection of components through reactions that form compounds with a characteristic color and shape of crystals observed under a microscope.

For qualitative chemical analysis, all known types of reactions are used: acid-base, redox, precipitation, complex formation, and others.

Qualitative analysis of solutions of inorganic substances is reduced to the detection of cations and anions. For this use general and private reactions. General reactions give a similar external effect (AC) with many ions (for example, the formation of precipitates of sulfates, carbonates, phosphates, etc. by cations), and private reactions with 2-5 ions. The fewer ions give a similar AS, the more selective (selective) the reaction is considered. The reaction is called specific when it allows one ion to be detected in the presence of all the others. Specific, for example, to the ammonium ion is the reaction:

NH 4 Cl + KOH  NH 3  + KCl + H 2 O

Ammonia is detected by smell or by the blue color of a red litmus paper soaked in water and placed over a test tube.

The selectivity of reactions can be increased by changing their conditions (pH) or by applying masking. masking is to reduce the concentration of interfering ions in the solution below the limit of their detection, for example, by binding them into colorless complexes.

If the composition of the analyzed solution is simple, then it is analyzed after masking fractional way. It consists in the detection of one ion in any sequence in the presence of all the others with the help of specific reactions that are carried out in separate portions of the analyzed solution. Since there are few specific reactions, when analyzing a complex ionic mixture, one uses systematic way. This method is based on separating a mixture into groups of ions with similar chemical properties by converting them into precipitates using group reagents, and the group reagents act on the same portion of the analyzed solution according to a certain system, in a strictly defined sequence. Precipitates are separated from each other (for example, by centrifugation), then dissolved in a certain way and a series of solutions is obtained, which makes it possible to detect an individual ion in each by a specific reaction to it.

There are several systematic methods of analysis, named after the group reagents used: hydrogen sulfide, acid-base, ammonia-phosphate other. The classical hydrogen sulfide method is based on the separation of cations into 5 groups by obtaining their sulfides or sulfur compounds when exposed to H 2 S, (NH 4) 2 S, NaS under various conditions.

More widely used, accessible and safe is the acid-base method, in which cations are divided into 6 groups (Table 1.3.1.). The group number indicates the sequence of exposure to the reagent.

Table 1.3.1

Classification of cations according to the acid-base method

Group number	Cations	Group reagent	Solubility of compounds
I	Ag + , Pb 2+ , Hg 2 2+	2MHCl	Chlorides are insoluble in water
II	Ca2+, Sr2+, Ba2+	1MH2SO4	Sulfates are insoluble in water
III	Zn 2+ , Al 3+ , Cr 3+ , Sn 2+ , Si 4+ , ​​As	4MNaOH	Hydroxides are amphoteric, soluble in excess alkali
IV	Mg 2+ , Mn 2+ , Fe 2+ , Fe 3+ , Bi 3+ , Sb 3+ , Sb 5+	25% NH 3	Hydroxides are insoluble in excess NaOH or NH 3
Group number	Cations	Group reagent	Solubility of compounds
V	Co 2+ , Ni 2+ , Cu 2+ , Cd 2+ , Hg 2+	25% NH 3	Hydroxides dissolve in excess NH 3 with the formation of complex compounds
VI	Na + , K + , NH 4 +	Not	Chlorides, sulfates, hydroxides are soluble in water

Anions in the analysis basically do not interfere with each other, therefore, group reagents are used not for separation, but to check the presence or absence of a particular group of anions. There is no consistent classification of anions into groups.

In the simplest way, they can be divided into two groups with respect to the Ba 2+ ion:

a) giving highly soluble compounds in water: Cl - , Br - , I - , CN - , SCN - , S 2- , NO 2 2- , NO 3 3- , MnO 4- , CH 3 COO - , ClO 4 - , ClO 3 - , ClO - ;

b) giving poorly soluble compounds in water: F -, CO 3 2-, CsO 4 2-, SO 3 2-, S 2 O 3 2-, SO 4 2-, S 2 O 8 2-, SiO 3 2-, CrO 4 2-, PO 4 3-, AsO 4 3-, AsO 3 3-.

Qualitative chemical analysis of organic substances is divided into elemental , functional , structural and molecular .

The analysis begins with preliminary tests of organic matter. For solids, measure t melt. , for liquid - t kip or , refractive index. The molar mass is determined by lowering t frozen or increasing t bale, that is, by cryoscopic or ebullioscopic methods. An important characteristic is solubility, on the basis of which there are classification schemes for organic substances. For example, if a substance does not dissolve in H 2 O, but dissolves in a 5% NaOH or NaHCO 3 solution, then it belongs to a group of substances that includes strong organic acids, carboxylic acids with more than six carbon atoms, phenols with substituents in ortho and para positions, -diketones.

Table 1.3.2

Reactions for the identification of organic compounds

Connection type	Functional group involved in the reaction	Reagent
Aldehyde	C = O	a) 2,4 - dinitrophenylhydrozide b) hydroxylamine hydrochloride c) sodium hydrogen sulfate
Amine	- NH2	a) nitrous acid b) benzenesulfonyl chloride
aromatic hydrocarbon	Azoxybenzene and aluminum chloride
Ketone	C = O	See aldehyde
unsaturated hydrocarbon	- C \u003d C - - C ≡ C -	a) KMnO 4 solution b) Br 2 solution in CCL 4
Nitro compound	- NO 2	a) Fe (OH) 2 (Mohr's salt + KOH) b) zinc dust + NH 4 Cl c) 20% NaOH solution
Alcohol	(R)-OH	a) (NH 4) 2 b) ZnCl 2 solution in HCl c) iodic acid
Phenol	(Ar)-OH	a) FeCl 3 in pyridine b) bromine water
Ether is simple	(R΄)- OR	a) hydroiodic acid b) bromine water
Ether complex	(R΄) - COOR	a) NaOH (or KOH) solution b) hydroxylamine hydrochloride

Elemental analysis detects elements included in the molecules of organic substances (C, H, O, N, S, P, Cl, etc.). In most cases, the organic matter is decomposed, the decomposition products are dissolved, and the elements in the resulting solution are determined as in inorganic substances. For example, when nitrogen is detected, the sample is fused with potassium metal to form KCN, which is treated with FeSO 4 and converted to K 4 . By adding to the latter a solution of Fe 3+ ions, Prussian blue Fe 4 3 - (AC for the presence of N) is obtained.

Qualitative Analysis can be used to identify atoms (elemental analysis), molecules (molecular analysis), simple or complex substances (material analysis), phases of a heterogeneous system (phase analysis) in the object under study. The task of qualitative inorganic analysis is usually reduced to the detection of cations or anions present in the analyzed sample. Qualitative analysis is necessary to justify the choice of a method for the quantitative analysis of a particular material or a method for separating a mixture of substances. Qualitative chemical analysis is used in agriculture and in solving environmental problems. In the agrochemical service, it is necessary for the recognition of mineral fertilizers, and in the control of environmental pollution - for the detection of pesticide residues, etc.

Types of chemical reactions.

pyrochemical reactions. A number of qualitative analysis methods are based on chemical reactions carried out by fusion, heating on charcoal, in the flame of a gas burner or blowtorch. In this case, substances are oxidized by oxygen in the air, and reduced by carbon monoxide, atomic carbon of a flame or charcoal. Oxidation or reduction can lead to the formation of colored products. One of the most commonly used pyrochemical reactions is the flame color test. The flame is painted in the color characteristic of the cation. The coloring of the flame with compounds of some elements is presented in the table.

	flame color		flame color
	carmine red		blue purple
			emerald green
	Violet		pale blue
	pink purple		pale blue
	pink purple		pale blue
	brick red		pale blue
Strontium	carmine red		emerald green
	yellow green		Green, blue
		Molybdenum	yellow green

Microcrystalloscopic reactions- these are reactions during which precipitation is formed, consisting of crystals of a characteristic shape and color. Determine the external shape of the crystals, which have a certain symmetry. Outgassing reactions- reactions in which gaseous compounds are released. Specific reagents are used to detect individual gases (hydrogen sulfide is detected with lead acetate - blackening, ammonia-phenolphthalein - redness in an alkaline environment). Color reactions- the main type of reactions for the detection of substances. The color is preserved in all compounds of colored cations and anions (manganates, chromates, dichromates). The color may appear and change depending on the conditions under the action of an ion of the opposite sign - for example, b / c iodine and silver ions form yellow-brown silver iodide.

The discovery of ions by specific reactions in a separate sample of the entire test solution in any sequence is called fractional analysis. The systematic course of analysis, in contrast to fractional analysis, consists in the fact that a mixture of ions with the help of special reagents is first divided into separate groups. From these groups, each ion is isolated in a certain sequence, and then it is already opened by a characteristic reaction. Reagents that allow in a certain sequence to separate ions into analytical groups are called group.

And substance analysis

Chemical identification

In the practice of specialists, it often becomes necessary to identify (detect) a particular substance, as well as quantify (measure) its content, which is the subject of study of analytical chemistry.

Analytical chemistry is the science of methods for determining the chemical composition of a substance and its structure.

In modern analytical chemistry, one can distinguish qualitative analysis, which solves the question of which components are part of the analyzed object, and quantitative analysis, which gives information about the quantitative content of the components. When conducting a qualitative and quantitative analysis, they measure analytical signal - a property of an analyte that makes it possible to judge the presence of certain components in it. This can be current strength, system emf, radiation intensity, color, etc.

Classification of types of analysis can be carried out according to various criteria. For example, depending on the amount of the analyte, the volume of solutions used for analysis, as well as the application of the technique for performing the experiment, analysis methods are divided into macro-, semi-micro-, micro- and ultra-microanalyses.

Semi-microanalysis has several advantages: it saves time and reagents, increases the reliability of the analysis results due to the use of more specific and highly sensitive reagents, and reduces the consumption of reagents and materials.

task qualitative analysis is the determination of chemical elements, ions, atoms, molecules, etc. in the analyzed substance (object).

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

The analysis of the test substance in qualitative chemical analysis can be carried out by "wet" and "dry" methods. In the first case, the analysis is carried out in solutions by adding appropriate reagents. In the second case, the determination of the composition of a substance is based on its ability to color a colorless flame of a burner in a characteristic color or give colored "pearls" when fused with borax. The discovery of individual ions in semi-microanalysis is carried out mainly by the "wet" method.

To discover ions in solutions, various characteristic reactions are used, which are accompanied by external effects - the appearance analytical signal, for example, a change in the color of the solution, the precipitation or dissolution of a precipitate, the evolution of gas.

Substances that are used to discover ions are called reagents into the corresponding ions, and the resulting chemical transformations - analytical reactions.

The reactions used in qualitative analysis should be fast, highly sensitive and, if possible, irreversible.

Sensitivity reactions determines the possibility of detecting a substance in a solution. It is characterized detection limit ( about opening minimum), limiting concentration, limiting dilution and minimum volume of extremely dilute solution.

Limit of detection is the minimum amount of a component that can be discovered using a given analytical reaction. The limit of detection is expressed in micrograms (µg), denoted by g (1g = 0.001 mg = 10–6 g).

Limit concentration is the lowest concentration C min), at which the analyte can be detected in solution by a given analytical reaction with a well-defined probability ( P), usually equal to one. Limit concentration designate C min, P and expressed in g/ml.

Ultimate dilution (V lim) is the maximum volume of a solution in which 1 g of a given substance can be detected using a given analytical reaction. The limiting dilution is expressed in ml/g.

The limiting concentration and limiting dilution are related by the relation

In qualitative analysis, only such reactions are used, the limit of detection (opening minimum) of which does not exceed 50 μg.

According to the number of components interacting under given conditions with the reagent used and giving an analytical signal, reactions and reagents are divided into group, selective and specific.

groupreactions are called when a whole group of ions interacts with a reagent under given conditions and gives an analytical signal, the reagent is called group. For example, S 2– at pH = 5 precipitates Ag +, Pb 2+, Bi 3+, Cd 2+, Sn 2+, 4+, etc. Therefore, S 2– is a group reagent, and the precipitation of sulfides is a group reaction. Group reactions are mainly used to separate entire groups of ions.

In laboratory practice, for systematic analysis of cations, the method based on the separation of cations according to the acid-base principle is most often used (Table 14.1.1).

Table 11.1.1

Acid-base classification of cations

group number	Name	Cations	Group Reagent
I	Soluble	Na + , K + , NH 4 +	No
II	chloride	Ag + , Pb 2+ , Hg 2 2+	2n HCl precipitates the corresponding chlorides
III	Sulfate	Ca2+, Ba2+, Sr2+	2n H 2 SO 4 precipitates the corresponding sulfates
IV	Amphoteric	Al 3+ , Cr 3+ , Zn 2+ , Sn 2+ , Sn 4+ , ​​As 3+ , As 5+	NaOH forms hydroxides soluble in excess of the reagent
V	hydroxide	Fe 2+ , Fe 3+ , Mn 2+ , Mg 2+ , Bi 3+ , Sb 3+, Sb 5+	2n NaOH precipitates the corresponding hydroxides
VI	Ammonia	Cu 2+ , Ni 2+ , Co 2+ , Cd 2+ , Hg 2+	2n NH 4 OH forms hydroxides that are soluble in excess of the reagent with the formation of ammonia

Electoral(selective) reactions are called when a limited number of components interact with the reagent under given conditions and give an analytical signal. Such a reagent is called selective. For example, a magnesia mixture (an ammonia solution of MgCl 2 and NH 4 Cl) forms a white finely crystalline precipitate with two PO 4 3– and AsO 4 3– ions. Selective reactions are used for both separation and detection of ions.

specificreactions are called when one component interacts with a reagent under given conditions and gives an analytical signal. The reagent is called specific. Such reactions are very convenient for detecting ions, but their number is limited. Some specific reagents for the identification of cations are presented in Table. 11.1.2.

Qualitative analysis is a technique used in analytical chemistry to identify ions within a substance. Let us analyze its features, as well as options for the practical application of elements in analytical chemistry.

Classification

Qualitative analysis is a method that involves dividing into several groups:

• chemical, which are based on some external effect;
• physical, allowing to determine the composition using thermal, magnetic, electrical properties;
• physico-chemical, based on the analysis of physical processes occurring as a result of chemical interactions.

When conducting experiments, the variety that is most suitable in a particular case is selected.

purpose

Qualitative analysis is the discovery of ions, chemical elements, molecules, groups in the analyzed sample of a substance. Its purpose is to detect certain ions or elements that are in the composition of the compound.

The definition of qualitative analysis explains the application within its framework of the physical and chemical properties of a substance.

Selectivity

Of the numerous chemical reactions, only those processes that are characterized by an external result are used to detect ions or elements. Qualitative analysis methods are effective in the formation of a precipitate, gas evolution, color change, energy release. All processes underlying the method are called analytical reactions.

Qualitative analysis is a method that is based on selective (specific) processes that occur in a particular ion (group of elements).

Reaction Requirements

There are certain requirements that apply to interactions in qualitative analysis:

• speed and irreversibility of the flow;
• external signs (precipitate, gas, color);
• high sensitivity

A specific reaction is such a reaction that makes it possible to detect the necessary element even in the case of its minimum concentrations, moreover, in the presence of other elements in the mixture.

Sensitivity is determined by the minimum amount of the detected element, at which it is detected without additional enrichment of the solution. This is an important characteristic of qualitative analysis, which makes it possible to talk about the effectiveness of the conducted (planned) experiment.

Methods

There are the following methods of qualitative and quantitative analysis:

• according to the number of detected particles: elementary, functional, phase, isotopic, molecular;
• by the amount of the compound taken for analysis: macro- (more than 100 mg, 5 ml), micro- (not more than 0.1 ml, 1 - mg), semi-micro - (medium range), ultramicro methods (substances are taken less than 0.1 mg, 0.05 ml);
• by defined object: organic and inorganic.

A little help

A brief description of qualitative and quantitative analysis allows us to understand their main differences. In a qualitative analysis, the sample can be in the form of a solution or a dry material in which several compounds are present at once. The analysis of the sample is carried out by a fractional technique, opening ions using certain qualitative reactions.

First, the presence of the ammonium cation is detected, since it is easiest to remove it from the mixture using reagents. Next, anions are identified, and the composition of the existing sample is summed up.

How to determine the ammonium cation

In order to discover these ions, two techniques are used in qualitative analysis. The first option is based on the addition of an alkali solution (active metal hydroxide). A few drops of the solution in question or an ammonium salt are treated with a solution of sodium (potassium) hydroxide. As a result of a qualitative reaction, the release of gaseous ammonia is observed. To detect it, indicator paper is used (phenolphthalein becomes crimson).

The second way to determine ammonium cations in a sample involves the use of Nessler's reagent. A few drops of it are treated with an excess of alkali to precipitate colored bases, which interfere with the observation of the precipitate resulting from the interaction with the Nessler reagent of the ammonium cation.

This reagent is a complex salt of potassium and mercury, which gives a red-brown precipitate with the ammonium cation. It is used to determine calcium cations in a mixture.

Determination of calcium cations

For qualitative analysis, it is permissible to use a microscopic reaction in the form of gypsum. One drop of concentrated sulfuric acid is added to a few drops of the analyzed solution. After a couple of minutes, transfer it to a glass slide, evaporate until a border forms. The result of the experiment is studied under a microscope.

The second option for the detection of calcium cations in the analyzed sample is based on the staining of the colorless flame of an alcohol lamp with volatile calcium salts in a saturated brick-red color.

Determination of iron cations

Divalent and trivalent iron is found from the initial solution, since under the action of some chemical reagents (hydrogen peroxide, alkali, hydrogen sulfide) the oxidation state changes from +2 to +3. To detect an iron cation with an oxidation state of +2, it is necessary to add a mixture of potassium hexacyanoferrate (3) and hydrochloric acid to the test solution. When a saturated blue precipitate of Prussian blue appears, we can talk about the content of Fe 2+ in the solution.

In order to determine trivalent iron, you need to add K 4 and salt to the solution. The appearance of a saturated blue color is confirmation of the presence of Fe 3+ in the solution.

Ways to detect Co2+, Ni2+, Cr3+

These cations have specific reactions, so they can be detected in portions of the initial solution. To detect the cobalt cation, sodium acetate is added dropwise to the existing solution until an acidic medium is obtained. Then sodium (or ammonium) fluoride and NH4NCS are added to the solution so that the iron cation is bound into a complex, then extracted with isoamyl alcohol.

When the complex compound is formed, the organic layer of the solvent turns blue.

To open the nickel cation in the analyzed solution, a sodium fluoride solution is used (ferrous and copper cations are removed), then ammonia and a few drops of dimethylglyoxime are added. In the presence of the nickel cation, a deep red precipitate is observed.

To identify the trivalent chromium cation, a few drops of a solution of acetic acid and sodium acetate, as well as an excess of complexone 3 (EDTA) are added to the solution. The whole mixture is then heated on a water bath. The appearance of a violet color indicates the presence of a trivalent chromium cation in the analyzed solution.

Definition of anions

To detect sulfate, interaction with barium chloride is used. To a few drops of a solution containing this anion, add a few drops of barium chloride. Barium sulfate is treated with a solution of nitric or hydrochloric acid, the resulting precipitate does not dissolve.

Carbonate can be detected in solution using a specific reaction with hydrochloric acid. In the presence of carbonate in solution, carbon dioxide is released.

Chloride can be found in the analyzed solution using silver nitrate. The appearance of a white cheesy precipitate is a confirmation of the presence of chloride.

Qualitative Analysis

Chapter 10. QUALITATIVE AND QUANTITATIVE ANALYSIS OF SUBSTANCES

Analytical chemistry – the science of methods for determining the chemical composition and structure of substances.

Chemical analysis is the basis of modern chemical-technological control and the establishment of state standards for manufactured products.

Task qualitative analysis -determination of the chemical composition of the test compound.

Qualitative analysis is carried out chemical, physical and physico-chemical methods. Physical and physico-chemical methods of analysis are based on the measurement of some parameter of the system, which is a function of the composition. So, in spectral analysis, the radiation spectra that arise when a substance is introduced into the burner flame are studied.

Chemical methods of qualitative analysis are based on the transformation of the analyte into new compounds with certain properties. By the formation of characteristic compounds of elements, the elemental composition of the substance is established. So, Cu 2+ ions can be detected by the formation of a complex 2+ ion of an azure blue color. The NH 4 + cation is detected by the release of gaseous ammonia NH 3 by the action of an alkali solution when heated.

Qualitative analytical reactions according to the method of their implementation are divided into reactions "wet" and "dry" way. The ʼʼʼʼʼ reactions are of the greatest importance. To conduct them, the test substance must be pre-dissolved. In qualitative analysis, only those reactions are used that are accompanied by any clearly visible external effects: a change in the color of the solution, the precipitation or dissolution of a precipitate, the evolution of gases with a characteristic odor or color, etc. Especially often used are reactions accompanied by the formation of precipitates and a change in the color of the solution. Such reactions are called ʼʼopeningʼʼ reactions, because with their help, the ions present in the solution are detected. Precipitation reactions are used to separate one group of ions from another or one ion from another.

Taking into account the dependence on the amount of the analyte, the volume of the solution and the technique for performing individual operations, chemical methods of qualitative analysis are divided into macro- (1-10 g or 10-100 ml of the test substance), semi-micro- (0.05-0.5 g or 1-10 ml), micro- (0.001-10 -6 g or 0.1-10 -4 ml), and ultramicroanalysis, etc.

Analysis "dry" way is carried out with solids. It is divided into rubbing analysis and pyrotechnic analysis. The latter is based on utem being carried out with solids. Separate operations chemical methods of qualitative analysis are divided into macro-, micro-, full heating of the test substance in a burner flame. Consider flame coloring reactions - volatile salts of many metals, when they are introduced into the non-luminous part of the burner flame, color the flame in various colors characteristic of these metals: Li and Sr - carmine-red color of the flame, Na - intense yellow, K - violet, Rb and Cs - pink-violet, Ca - orange-red, Ba - green, Cu and B - yellow-green, Pb and As - pale blue, etc.

Sensitivity of analytical reactions - then the smallest amount of a substance (ion), ĸᴏᴛᴏᴩᴏᴇ, can be opened with this reagent. Quantitatively, the sensitivity of reactions is characterized by three indicators: opening minimum, limiting concentration, dilution limit.

In analytical practice, the ion to be determined usually has to be discovered in the presence of other ions. Reactions and reagents that make it possible to open a given ion in the presence of others are called specific.

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