1. Qualitative reactions to cations.
1.1.1 Qualitative reactions to alkali metal cations (Li + , Na + , K + , Rb + , Cs +).
Alkali metal cations can only be carried out with dry salts, because almost all alkali metal salts are soluble. You can detect them by adding a small amount of salt to the burner flame. One or another cation colors the flame in the corresponding color:
Li + - dark pink.
Na + - yellow.
K + - purple.
Rb+ - red.
Cs + - blue.
Cations can also be detected using chemical reactions. When a solution of lithium salt is poured with phosphates, an insoluble in water, but soluble in conc. nitric acid, lithium phosphate:
3Li + + PO4 3- = Li 3 PO 4 ↓
Li 3 PO 4 + 3HNO 3 \u003d 3LiNO 3 + H 3 PO 4

The K + cation can be derived with the hydrotartrate anion HC 4 H 4 O 6 - - anion of tartaric acid:
K + + HC 4 H 4 O 6 - = KHC 4 H 4 O 6 ↓

Cations K + and Rb + can be detected by adding to solutions of their salts of fluorosilic acid H 2 or its salts - hexafluorosilicates:
2Me + + 2- = Me 2 ↓ (Me = K, Rb)

They and Cs + are precipitated from solutions when perchlorate anions are added:
Me + + ClO 4 - = MeClO 4 ↓ (Me = K, Rb, Cs).

1.1.2 Qualitative reactions to alkaline earth metal cations (Ca 2+ , Sr 2+ , Ba 2+ , Ra 2+).
Alkaline earth metal cations can be detected in two ways: in solution and by the color of the flame. By the way, calcium, strontium, barium and radium belong to the alkaline earth. Beryllium and magnesium it is forbidden attributed to this group, as they like to do on the Internet.
Flame Color:
Ca 2+ - brick red.
Sr 2+ - carmine red.
Ba 2+ - yellowish green.
Ra 2+ - dark red.

Reactions in solutions. The cations of the metals under consideration have a common feature: their carbonates and sulfates are insoluble. The Ca 2+ cation is preferred to be detected by the carbonate anion CO 3 2-:
Ca 2+ + CO 3 2- \u003d CaCO 3 ↓
Which is easily soluble in nitric acid with the release of carbon dioxide:
2H + + CO 3 2- \u003d H 2 O + CO 2
Ba 2+, Sr 2+ and Ra 2+ cations are preferred to be detected by the sulfate anion with the formation of sulfates that are insoluble in acids:
Sr 2+ + SO 4 2- = SrSO 4 ↓
Ba 2+ + SO 4 2- \u003d BaSO 4 ↓
Ra 2+ + SO 4 2- = RaSO 4 ↓

1.1.3. Qualitative reactions to lead (II) Pb 2+, silver (I) Ag +, mercury (I) Hg 2 +, mercury (II) Hg 2+ cations. Consider them on the example of lead and silver.
This group of cations has one common feature: they form insoluble chlorides. But lead and silver cations can also be detected by other halides.

A qualitative reaction to the lead cation is the formation of lead chloride (white precipitate), or the formation of lead iodide (bright yellow precipitate):
Pb 2+ + 2I - = PbI 2 ↓

A qualitative reaction to the silver cation is the formation of a white cheesy precipitate of silver chloride, a yellowish-white precipitate of silver bromide, the formation of a yellow precipitate of silver iodide:
Ag + + Cl - = AgCl↓
Ag + + Br - = AgBr↓
Ag + + I - = AgI↓
As can be seen from the above reactions, silver halides (except fluoride) are insoluble, and bromide and iodide even have a color. But this is not their distinguishing feature. These compounds decompose under the influence of light into silver and the corresponding halogen, which also helps to identify them. Therefore, containers with these salts often emit odors. Also, when sodium thiosulfate is added to these precipitates, dissolution occurs:
AgHal + 2Na 2 S 2 O 3 = Na 3 + NaHal, (Hal = Cl, Br, I).
The same will happen when adding liquid ammonia or its conc. solution. Only AgCl dissolves. AgBr and AgI in ammonia are practically insoluble:
AgCl + 2NH 3 = Cl

There is also another qualitative reaction to the silver cation - the formation of black silver oxide when alkali is added:
2Ag + + 2OH - = Ag 2 O↓ + H 2 O
This is due to the fact that silver hydroxide does not exist under normal conditions and immediately decomposes into oxide and water.

1.1.4. Qualitative reaction to aluminum cations Al 3+, chromium (III) Cr 3+, zinc Zn 2+, tin (II) Sn 2+. These cations are united by the formation of insoluble bases, which are easily converted into complex compounds. Group reagent - alkali.
Al 3+ + 3OH - \u003d Al (OH) 3 ↓ + 3OH - \u003d 3-
Cr 3+ + 3OH - \u003d Cr (OH) 3 ↓ + 3OH - \u003d 3-
Zn 2+ + 2OH - \u003d Zn (OH) 2 ↓ + 2OH- \u003d 2-
Sn 2+ + 2OH- \u003d Sn (OH) 2 ↓ + 2OH - \u003d 2-
Do not forget that the bases of the Al 3+, Cr 3+ and Sn 2+ cations are not converted into a complex compound by ammonia hydrate. This is used to completely precipitate the cations. Zn 2+ when adding conc. ammonia solution first forms Zn (OH) 2, and with an excess of ammonia contributes to the dissolution of the precipitate:
Zn (OH) 2 + 4NH 3 \u003d (OH) 2

1.1.5. Qualitative reaction to iron (II) and (III) cations Fe 2+, Fe 3+. These cations also form insoluble bases. The Fe 2+ ion corresponds to iron (II) hydroxide Fe (OH) 2 - a white precipitate. In air, it immediately becomes covered with a green coating, so pure Fe (OH) 2 is obtained in an atmosphere of inert gases or nitrogen N 2.
The iron (III) metahydroxide FeO(OH) of brown color corresponds to the Fe 3+ cation. Note: Fe(OH) 3 compounds are unknown (not obtained). But still, most adhere to the notation Fe (OH) 3.
Qualitative reaction for Fe 2+:
Fe 2+ + 2OH - \u003d Fe (OH) 2 ↓
Fe (OH) 2 being a divalent iron compound in air is unstable and gradually turns into iron (III) hydroxide:
4Fe(OH) 2 + O 2 + 2H 2 O = 4Fe(OH) 3

Qualitative reaction for Fe 3+:
Fe 3+ + 3OH - \u003d Fe (OH) 3 ↓
Another qualitative reaction for Fe 3+ is the interaction with the thiocyanate anion SCN -, with the formation of iron thiocyanate (III) Fe (SCN) 3, coloring the solution in a dark red color ("blood" effect):
Fe 3+ + 3SCN - \u003d Fe (SCN) 3
Iron (III) thiocyanate is easily "destroyed" by the addition of alkali metal fluorides:
6NaF + Fe(SCN) 3 = Na 3 + 3NaSCN
The solution becomes colorless.
Very sensitive reaction for Fe 3+, helps to detect even very small traces of this cation.

1.1.6. Qualitative reaction to the manganese (II) cation Mn 2+. This reaction is based on the severe oxidation of manganese in an acidic environment with a change in the oxidation state from +2 to +7. In this case, the solution turns dark purple due to the appearance of the permanganate anion. Consider the example of manganese nitrate:
2Mn(NO 3) 2 + 5PbO 2 + 6HNO 3 = 2HMnO 4 + 5Pb(NO 3) 2 + 2H 2 O

1.1.7. Qualitative reaction to copper (II) Cu 2+, cobalt (II) Co 2+ and nickel (II) Ni 2+ cations. The peculiarity of these cations is the formation of complex salts - ammoniates with ammonia molecules:
Cu 2+ + 4NH 3 \u003d 2+
Ammonia dyes solutions in bright colors. For example, copper ammonia turns the solution bright blue.

1.1.8. Qualitative reactions to the ammonium cation NH 4 +. The interaction of ammonium salts with alkalis during boiling:
NH 4 + + OH - \u003d t \u003d NH 3 + H 2 O
When presented, wet litmus paper turns blue.

1.1.9. Qualitative reaction to the cerium (III) cation Ce 3+. Interaction of salts of cerium (III) with an alkaline solution of hydrogen peroxide:
Ce 3+ + 3OH - \u003d Ce (OH) 3 ↓
2Ce(OH) 3 + 3H 2 O 2 = 2Ce(OH) 3 (OOH)↓ + 2H 2 O
Cerium (IV) peroxohydroxide has a red-brown color.

1.2.1. Qualitative reaction to the cation of bismuth (III) Bi 3+. The formation of a bright yellow solution of potassium tetraiodobismuthate (III) K under the action of an excess of KI on a solution containing Bi 3+:
Bi(NO 3) 3 + 4KI = K + 3KNO 3
This is due to the fact that at first insoluble BiI 3 is formed, which is then associated with the help of I - into a complex.
This concludes the description of the detection of cations. Let us now consider qualitative reactions to some anions.

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Goals: to systematize students' ideas about qualitative reactions to some cations and anions, organic substances. Preparation for the exam.

Lesson objectives:

• Educational: to systematize, generalize and deepen students' knowledge of qualitative reactions.
• educators: to prove the leading role of theory in the knowledge of practice; to prove the materiality of the processes under study; education of independence, cooperation, ability to help each other, culture of speech, diligence, perseverance.
• Educational: development of the ability to analyze; the ability to use the studied material for learning new things; memory, attention, logical thinking.

Lesson type: lesson-lecture with elements of complex application of knowledge, skills and abilities.

During the classes

Introduction by the teacher.

Separate methods and techniques of chemical analysis were known in ancient times. Even then, they could carry out analyzes of medicines, metal ores.

English scientist Robert Boyle (1627 - 1691) is considered the founder of qualitative analysis.

The main task of qualitative analysis is the detection of substances that are in the object of interest to us (biological materials, drugs, food, environmental objects). The school course deals with the qualitative analysis of inorganic substances (which are electrolytes, i.e., in fact, the qualitative analysis of ions) and some organic compounds.

The science of methods for determining the qualitative and quantitative composition of substances or their mixtures by the intensity of an analytical signal is called analytical chemistry. Analytical chemistry develops the theoretical foundations of methods for studying the chemical composition of substances and their practical application. The task of qualitative analysis is the detection of components (or ions) contained in a given substance.

Studies of a substance always begin with its qualitative analysis, i.e., from the determination of which components (or ions) this substance consists of.

The theoretical foundations of chemical analysis are the following laws and theoretical provisions: D.I. Mendeleev; law of acting masses; theory of electrolytic dissociation; chemical equilibrium in heterogeneous systems; complexation; amphotericity of hydroxides; autoprotolysis (hydrogen and hydroxide indicators); OVR.

Chemical methods are based on transformations occurring in solutions with the formation of precipitates, colored compounds or gaseous substances. Chemical processes used for analysis purposes are called analytical reactions. Analytical reactions are those that are accompanied by some external effect, which makes it possible to establish that the chemical process is associated with the precipitation or dissolution of a precipitate, a change in the color of the analyzed solution, and the release of gaseous substances. Requirements for analytical reactions and their features can be reduced to the following provisions:

performing the analysis by the “dry” or “wet” method (dry method is pyrochemical methods, from the Greek “feast” - fire), this should include samples for coloring the flame during the combustion of the test substance on a loop of platinum (or nichrome) wire to obtain the result of a flame dyed in a characteristic color; a method of triturating a solid analyte with a solid reagent, for example, triturating a mixture of an ammonium salt with Ca(OH) 2 releases ammonia. Dry method analysis is used for express analyzes or in the field for qualitative and semi-quantitative studies of minerals and ores;

for wet analysis, the test substance must be transferred into solution and further reactions proceed as ion detection reactions.

An analytical reaction must proceed quickly and completely under certain conditions: temperature, reaction of the medium and concentration of the ion to be detected. When choosing an ion detection reaction, they are guided by the law of mass action and ideas about chemical equilibrium in solutions. In this case, the following characteristics of analytical reactions are distinguished: selectivity or selectivity; specificity; sensitivity. The latter characteristic is related to the concentration of the detectable ion in the solution, and if the reaction succeeds at a low ion concentration, then one speaks of a highly sensitive reaction. For example, if a substance is poorly soluble in water and a precipitate precipitates at its low concentration, then this is a highly sensitive reaction, if the substance is highly soluble and precipitates at a high ion concentration, then the reaction is considered insensitive. The concept of sensitivity refers to all analytical reactions, no matter what external effect they are accompanied by.

Let us consider the most characteristic qualitative reactions of the school course.

At the end of the lecture, students can be offered a control test using questions from the USE tests on this topic.

In the school chemistry course, students' acquaintance with indicators comes down mainly to litmus, methyl orange and phenolphthalein. Meanwhile, there are many more chemical indicators.

Here is one of the most common definitions of an indicator: indicator is a substance that indicates the state of the system or the moment at which the system reaches the required equilibrium. For chemists, it is important that the indicator by its state indicates the presence of a sufficient concentration of the analyte.

To make the indicator usable in practice, changing it states should be easy to fix. As a rule, indicators under the influence of the analyte change color, sometimes - aggregate state, fluoresce. There are acid-base indicators (pH indicators), redox indicators (redox indicators), as well as indicators for any specific substance or group of substances. The basic principle of the indicator is the interaction with the substance to be determined with the formation of a form that has other properties than the original one.

In particular, pH indicators are organic acids, bases or salts. For example, methyl orange is a yellow organic Lewis base, which, under the action of an acid (H + ions), turns into a red salt:

The reaction is reversible: when alkali is added to the salt, the H + ions associated with nitrogen atoms will interact with OH ions - to form water molecules and the equilibrium will shift towards the base. Therefore, when alkalized, methyl orange will turn yellow again.

The principle of action of phenolphthalein is about the same. Phenolphthalein is a colorless lactone that forms the raspberry acid anion under the action of a base:

Below are various indicators, however, for a school chemistry course, it is enough to know such indicators as litmus, methyl orange and phenophthalein:

Qualitative reactions to inorganic substances and ions. Cations

Qualitative Analysis- a section of analytical chemistry devoted to establishing the qualitative composition of substances, that is, the detection of elements and the ions they form, which are part of both simple and complex substances. This is done using chemical reactions characteristic of a given cation or anion, which make it possible to detect them both in individual substances and in mixtures.

The task of qualitative analysis is to study the methods by which it is established, what chemical elements included in the analyzed sample.

Chemical methods of analysis are based on the application characteristic chemical reactions to discover the constituent parts of matter. The substances used for these reactions are called reagents.

According to the theory of electrolytic dissociation, reactions occur between electrolyte ions formed in aqueous solutions. The chemical processes that take place are called analytical reactions.

They are accompanied characteristic external features easily perceived by our senses:

release of gas

change in the color of the solution

sedimentation

sediment dissolution

the formation of crystals of a characteristic shape

In the first four cases, the course of the reaction is observed visually, the crystals are examined under a microscope.

To obtain correct results, reactions are required that are not interfered with by other ions present. For this you need specific(interacting only with the ion being determined) or at least selective (selective) reagents.

An example of a reaction involving a specific reagent is the evolution of gaseous NH 3 by the action of strong bases (KOH or NaOH) on a substance containing an NH 4 + ion. Not a single cation interferes with the detection of the NH 4 + ion, because only it reacts with alkalis to release NH 3 .

Dimethylglyoxime (Chugaev's reagent) is an example of a selective reagent: in an alkaline medium, it reacts with Ni 2+, Co 2+, Fe 2+ ions, and in an acidic medium, only with Pd 2+ ions.

Unfortunately, there are very few selective, let alone specific, reagents; therefore, when analyzing a complex mixture, one has to resort to masking interfering ions by converting them into a reaction inert form, or, more often, to separating a mixture of cations or anions into constituent parts, called analytical groups. This is done with the help of special (group) reagents, which, reacting with a number of ions under the same conditions, form compounds with similar properties - sparingly soluble precipitates or stable soluble complexes. This allows you to divide a complex mixture into simpler components.

There are several schemes for dividing cations into analytical groups using group reagents. One of them is based on the use of differences in the solubility of chlorides, sulfates and hydroxides. By acting on a mixture of cations in a strictly defined order with solutions of HCl, H 2 SO 4 , NH 3 and NaOH (group reagents), the cations contained in the mixture can be divided into 6 analytical groups. This scheme is called acid-base by the names of the group reagents used in it.

See the qualitative reactions to cations in the table below:

Qualitative reactions to anions

Anions do not have a generally established division into groups, the number of which varies significantly in different analysis schemes. Usually, anions are classified on the basis of the solubility of salts and on the basis of redox activity.

Group reagents in the analysis of anions serve only for their detection (unlike cations, where such reagents also serve for separation).

See the qualitative reactions for anions in the table below:

Identification of organic compounds

Organic chemistry, as you know, is the chemistry of hydrocarbons and their derivatives.

Hydrocarbons are made up of the elements carbon and hydrogen. In addition to carbon and hydrogen, hydrocarbon derivatives may contain oxygen, nitrogen, sulfur, halogens and other elements.

To detect certain elements in the composition of an organic compound, the destruction of its molecule and the conversion of its constituent elements into the simplest compounds are required.

Analysis of the elemental composition can be carried out as a qualitative determination of the elements that make up organic compounds (C, H, O, N, S, Cl), and quantitative, showing the percentage of each element in the analyzed organic compound.

The presence of certain elements in an organic compound can be detected by various methods of qualitative analysis.

Halogens, for example, can be detected by a qualitative Beilstein test by changing the color of the flame when a copper wire with a sample of the analyzed substance is introduced into the flame of a gas burner, which is explained by the formation of volatile copper halides at high temperatures. This sample is sensitive even to the presence of traces of halogen in organic compounds.

Flame color test

A number of elements paint the flame in a characteristic color if, under the influence of heat, individual atoms of these elements appear in the flame. For some elements, the atoms are separated already during the first immersion in the flame, for others this requires treatment with acid. If there are no other special instructions in the determinant, then a mineral fragment must be moistened with a drop of dilute hydrochloric acid, which is applied with a glass rod or pipette, and then ignited.

When an electron makes a quantum jump from one allowed orbital to another, the atom emits light. And since the energy levels of the atoms of the two elements are different, the light emitted by an atom of one element will be different from the light emitted by an atom of the other. This is the basis of the science we call spectroscopy.

On the same position (that the atoms of different elements emit light of different wavelengths) the test for coloring the flame in chemistry is based. When a solution containing ions of one of the alkali metals (that is, one of the elements of the first column of the periodic system of Mendeleev) is heated in a gas burner flame, the flame will turn a certain color depending on which metal is present in the solution. For example, a bright yellow flame indicates the presence of sodium, purple - potassium, and carmine red - lithium. This coloring of the flame occurs as follows: a collision with the hot gases of the flame transfers the electrons to an excited state, from which they return to their original state, simultaneously emitting light of a characteristic wavelength.

This property of atoms explains why wood nailed to the ocean shore is so highly valued for stoking fireplaces. Being at sea for a long time, the logs adsorb a large number of different substances, and when the logs burn, these substances color the flame in many different colors.

Reference material for passing the test:

periodic table

Solubility table

1. Qualitative reactions to cations.
1.1. Qualitative reactions to alkali metal cations (Li + , Na + , K + , Rb + , Cs +).
Alkali metal cations can be detected by adding a small amount of salt to the burner flame. One or another cation colors the flame in the corresponding color:
Li + - dark pink.
Na + - yellow.
K + - purple.
Rb+ - red.
Cs + - blue.
Cations can also be detected using chemical reactions. When a solution of lithium salt is poured with phosphates, an insoluble in water, but soluble in conc. nitric acid, lithium phosphate:
3Li + + PO4 3- = Li 3 PO 4 ↓
Li 3 PO 4 + 3HNO 3 \u003d 3LiNO 3 + H 3 PO 4

Cations K + and Rb + can be detected by adding to solutions of their salts of fluorosilic acid H 2 or its salts - hexafluorosilicates:
2Me + + 2- = Me 2 ↓ (Me = K, Rb)

They and Cs + are precipitated from solutions when perchlorate anions are added:
Me + + ClO 4 - = MeClO 4 ↓ (Me = K, Rb, Cs).

1.2. Qualitative reactions to cations of alkaline earth metals (Ca 2+, Sr 2+, Ba 2+).
Alkaline earth metal cations can be detected in two ways: in solution and by the color of the flame. By the way, calcium, strontium, barium belong to the alkaline earth.
Flame Color:
Ca 2+ - brick red.
Sr 2+ - carmine red.
Ba 2+ - yellowish green.

Reactions in solutions. The cations of the metals under consideration have a common feature: their carbonates and sulfates are insoluble. The Ca 2+ cation is preferred to be detected by the carbonate anion CO 3 2-:
Ca 2+ + CO 3 2- \u003d CaCO 3 ↓
Which is easily soluble in nitric acid with the release of carbon dioxide:
2H + + CO 3 2- \u003d H 2 O + CO 2
Ba 2+, Sr 2+ cations are preferred to be detected by the sulfate anion with the formation of sulfates that are insoluble in acids:
Sr 2+ + SO 4 2- = SrSO 4 ↓
Ba 2+ + SO 4 2- \u003d BaSO 4 ↓

1.3. Qualitative reactions to lead (II) Pb 2+, silver (I) Ag +, mercury (I) Hg +, mercury (II) Hg 2+ cations. Consider them on the example of lead and silver.
This group of cations has one common feature: they form insoluble chlorides. But lead and silver cations can also be detected by other halides.

A qualitative reaction to the lead cation is the formation of lead chloride (white precipitate), or the formation of lead iodide (bright yellow precipitate):
Pb 2+ + 2I - = PbI 2 ↓

A qualitative reaction to the silver cation is the formation of a white cheesy precipitate of silver chloride, a yellowish-white precipitate of silver bromide, the formation of a yellow precipitate of silver iodide:
Ag + + Cl - = AgCl↓
Ag + + Br - = AgBr↓
Ag + + I - = AgI↓
As can be seen from the above reactions, silver halides (except fluoride) are insoluble, and bromide and iodide are colored. But this is not their distinguishing feature. These compounds decompose under the influence of light into silver and the corresponding halogen, which also helps to identify them. Therefore, containers with these salts often emit odors. Also, when sodium thiosulfate is added to these precipitates, dissolution occurs:
AgHal + 2Na 2 S 2 O 3 = Na 3 + NaHal, (Hal = Cl, Br, I).
The same will happen when adding liquid ammonia or its conc. solution. Only AgCl dissolves. AgBr and AgI in ammonia are practically insoluble:
AgCl + 2NH 3 = Cl

There is also another qualitative reaction to the silver cation - the formation of black silver oxide when alkali is added:
2Ag + + 2OH - = Ag 2 O↓ + H 2 O
This is due to the fact that silver hydroxide does not exist under normal conditions and immediately decomposes into oxide and water.

1.4. Qualitative reaction to aluminum cations Al 3+, chromium (III) Cr 3+, zinc Zn 2+, tin (II) Sn 2+. These cations are united by the formation of insoluble bases, which are easily converted into complex compounds. Group reagent - alkali.
Al 3+ + 3OH - \u003d Al (OH) 3 ↓ + 3OH - \u003d 3-
Cr 3+ + 3OH - \u003d Cr (OH) 3 ↓ + 3OH - \u003d 3-
Zn 2+ + 2OH - \u003d Zn (OH) 2 ↓ + 2OH- \u003d 2-
Sn 2+ + 2OH- \u003d Sn (OH) 2 ↓ + 2OH - \u003d 2-
Do not forget that the bases of the Al 3+, Cr 3+ and Sn 2+ cations are not converted into a complex compound by ammonia hydrate. This is used to completely precipitate the cations. Zn 2+ when adding conc. ammonia solution first forms Zn (OH) 2, and with an excess of ammonia contributes to the dissolution of the precipitate:
Zn (OH) 2 + 4NH 3 \u003d (OH) 2

1.5. Qualitative reaction to iron (II) and (III) cations Fe 2+, Fe 3+. These cations also form insoluble bases. The Fe 2+ ion corresponds to iron (II) hydroxide Fe (OH) 2 - a white precipitate. In air, it immediately becomes covered with a green coating, so pure Fe (OH) 2 is obtained in an atmosphere of inert gases or nitrogen N 2.
The iron (III) metahydroxide FeO(OH) of brown color corresponds to the Fe 3+ cation. Note: Fe(OH) 3 compounds are unknown (not obtained). But still, most adhere to the notation Fe (OH) 3.
Qualitative reaction for Fe 2+:
Fe 2+ + 2OH - \u003d Fe (OH) 2 ↓
Fe (OH) 2 being a divalent iron compound in air is unstable and gradually turns into iron (III) hydroxide:
4Fe(OH) 2 + O 2 + 2H 2 O = 4Fe(OH) 3

Qualitative reaction for Fe 3+:
Fe 3+ + 3OH - \u003d Fe (OH) 3 ↓
Another qualitative reaction for Fe 3+ is the interaction with the thiocyanate anion SCN -, with the formation of iron thiocyanate (III) Fe (SCN) 3, coloring the solution in a dark red color ("blood" effect):
Fe 3+ + 3SCN - \u003d Fe (SCN) 3
Iron (III) thiocyanate is easily "destroyed" by the addition of alkali metal fluorides:
6NaF + Fe(SCN) 3 = Na 3 + 3NaSCN
The solution becomes colorless.
Very sensitive reaction for Fe 3+, helps to detect even very small traces of this cation.

1.6. Qualitative reaction to the manganese (II) cation Mn 2+. This reaction is based on the severe oxidation of manganese in an acidic environment with a change in the oxidation state from +2 to +7. In this case, the solution turns dark purple due to the appearance of the permanganate anion. Consider the example of manganese nitrate:
2Mn(NO 3) 2 + 5PbO 2 + 6HNO 3 = 2HMnO 4 + 5Pb(NO 3) 2 + 2H 2 O

1.7. Qualitative reaction to copper (II) Cu 2+, cobalt (II) Co 2+ and nickel (II) Ni 2+ cations. The peculiarity of these cations is the formation of complex salts - ammoniates with ammonia molecules:
Cu 2+ + 4NH 3 \u003d 2+
Ammonia dyes solutions in bright colors. For example, copper ammonia turns the solution bright blue.

Ions and cations make it possible to determine the presence of various compounds using available, in most cases, simple methods. They can be carried out using indicators, hydroxides, oxides. The science that studies the properties and structure of various substances is called "chemistry". Qualitative reactions are part of the practical section of this science.

Classification of inorganic substances

All substances are divided into organic and inorganic. The former include such classes of compounds as salts, hydroxides (bases, acids and amphoteric) and oxides, as well as simple compounds (CI2, I2, H2 and others consisting of one element).

Salts consist of a metal cation and an anion of an acid residue. The composition of acid molecules includes H+ cations and anions of acid residues. Hydroxides are composed of metal cations and anions in the form of the OH- hydroxyl group. The composition of oxide molecules includes atoms of two chemical elements, one of which is necessarily oxygen. They can be acidic, basic and amphoteric. As their name implies, they are able to form various classes of substances in the course of certain reactions. Thus, acidic oxides react with water to form acids, while basic oxides form bases. Amphoteric, depending on the conditions, can exhibit the properties of both types of oxides. These include beryllium, aluminum, tin, chromium, lead. Their hydroxides are also amphoteric. To determine the presence of various inorganic substances in a solution, qualitative reactions for ions are used.

Diversity of organic matter

This group includes chemical compounds, the molecules of which necessarily include carbon and hydrogen. They can also contain atoms of oxygen, nitrogen, sulfur and many other elements.

They are divided into such main classes: alkanes, alkenes, alkynes, organic acids (nucleic, fatty, saturated, amino acids and others), aldehydes, proteins, fats, carbohydrates. Many qualitative reactions on organic substances are carried out using a variety of hydroxides. Reagents such as potassium permanganate, acids, oxides can also be used for this.

Qualitative reactions to organic substances

The presence of alkanes is mainly determined by the exclusion method. If you add potassium permanganate, it will not discolour. These substances burn with a light blue flame. Alkenes can be detected by adding either potassium permanganate. Both of these substances become colorless when interacting with them. The presence of phenol can also be determined by adding a solution of bromine. At the same time, it will discolor and precipitate. In addition, the presence of this substance can be detected using a solution of ferric chloride, which, when interacting with it, will give a violet-brown color. Qualitative reactions to organic substances of the class of alcohols consist in the addition of sodium to them. In this case, hydrogen will be released. The burning of alcohols is accompanied by a light blue flame.

Glycerin can be detected using cuprum hydroxide. In this case, glycerates are formed, which give the solution a cornflower blue color. The presence of aldehydes can be determined using argentum oxide. As a result of this reaction, pure argentum is released, which precipitates.

There is also a qualitative reaction to aldehydes, which is carried out with the help of To carry out it, it is necessary to heat the solution. At the same time, he should change color first from blue to yellow, then to red. Proteins can be detected using nitrate acid. As a result, a yellow precipitate is formed. If you add cuprum hydroxide, it will be purple. Qualitative reactions to organic substances of the class of acids are carried out using litmus or In both cases, the solution changes its color to red. If sodium carbonate is added, carbon dioxide will be released.

Qualitative reactions to cations

They can be used to determine the presence of any metal ions in a solution. Qualitative reactions to acids consist in identifying the H + cation, which is part of their composition. This can be done in two ways: using litmus or methyl orange. The first in an acidic environment changes its color to red, the second to pink.

Lithium, sodium and potassium cations can be distinguished by their flames. The former burn red, the latter yellow, and the third violet. Calcium ions are detected by adding carbonate solutions, resulting in a white precipitate.

Qualitative reactions to anions

The most common of these is the detection of OH-, as a result of which it is possible to find out whether bases are present in the solution. This requires indicators. These are phenolphthalein, methyl orange, litmus. The first in such an environment acquires the second - yellow, the third - blue.