Practical work No. 1

Reagents : paraffin (C 14 H 30

Equipment :

Note:

2. The halogen in organic matter can be detected by the flame color reaction.

Work algorithm:

Pour lime water into the receiver tube.

Connect the test tube with the mixture to the test tube with a gas outlet tube with a stopper.

Heat the test tube with the mixture in the flame of an alcohol lamp.

Ignite the copper wire in the flame of an alcohol lamp until a black coating appears on it.

Bring the cooled wire into the test substance and again bring the spirit lamp into the flame.

Conclusion:

pay attention to: changes occurring with lime water, copper sulfate (2).

What color does the flame of the spirit lamp turn into when the test solution is added?

Practical work No. 1

"Qualitative analysis of organic compounds".

Reagents: paraffin (C 14 H 30 ), lime water, copper oxide (2), dichloroethane, copper sulfate (2).

Equipment : metal stand with foot, spirit lamp, 2 test tubes, cork with gas tube, copper wire.

Note:

carbon and hydrogen can be detected in organic matter by its oxidation with copper oxide (2).

halogen in organic matter can be detected using a flame color reaction.

Work algorithm:

1st stage of work: Melting of paraffin with copper oxide

1. Assemble the device according to fig. 44 on page 284, for this, place 1-2 g of copper oxide and paraffin in the bottom of the test tube, heat it up.

2nd stage of work: Qualitative determination of carbon.

1. Pour lime water into the receiver tube.

2. Connect the test tube with the mixture to the test tube with a gas outlet tube with a stopper.

3.Heat the test tube with the mixture in the flame of an alcohol lamp.

3rd stage of work: Qualitative determination of hydrogen.

1. In the upper part of the test tube with the mixture, place a piece of cotton wool, putting copper sulfate (2) on it.

4th stage of work: Qualitative determination of chlorine.

1. Ignite the copper wire in the flame of an alcohol lamp until a black coating appears on it.

2. Insert the cooled wire into the test substance and again bring the spirit lamp into the flame.

Conclusion:

1. pay attention to: changes occurring with lime water, copper sulfate (2).

2. What color is the flame of the spirit lamp colored when the test solution is added.

Most drugs used in medical practice are organic substances.

To confirm that a drug belongs to a particular chemical group, it is necessary to use identification reactions that should detect the presence of a certain functional group in its molecule (for example, an alcohol or phenolic hydroxyl, a primary aromatic or aliphatic group, etc.). Such an analysis is called a functional group analysis.

Analysis by functional groups is based on the knowledge acquired by students in the study of organic and analytical chemistry.

Information

Functional groups - these are groups of atoms that are highly reactive and easily interact with various reagents with a noticeable specific analytical effect (color change, odor, gas or precipitate, etc.).

Identification of preparations by structural fragments is also possible.

Structural fragment - this is the part of the drug molecule that interacts with the reagent with a noticeable analytical effect (for example, anions of organic acids, multiple bonds, etc.).

Functional groups

Functional groups can be divided into several types:

2.2.1. containing oxygen:

a) hydroxyl group (alcohol and phenolic hydroxyl):

b) aldehyde group:

c) keto group:

d) carboxyl group:

e) ester group:

f) simple ether group:

2.2.2. Containing nitrogen:

a) primary aromatic and aliphatic amino groups:

b) secondary amino group:

c) tertiary amino group:

d) amide group:

e) nitro group:

2.2.3. Sulfur containing:

a) thiol group:

b) sulfamide group:

2.2.4. Halogen containing:

2.3. Structural fragments:

a) double bond:

b) phenyl radical:

2.4. Anions of organic acids:

a) Acetate ion:

b) tartrate ion:

c) citrate ion:

d) benzoate ion:

This methodological manual provides the theoretical foundations for the qualitative analysis of structural elements and functional groups of the most common methods of analysis of medicinal substances in practice.

2.5. IDENTIFICATION OF ALCOHOLIC HYDROXYL

Medicines containing alcohol hydroxyl:

a) Ethyl alcohol

b) Methyltestosterone

c) Menthol

2.5.1. Esters formation reaction

Alcohols in the presence of concentrated sulfuric acid form esters with organic acids. Low molecular weight ethers have a characteristic odor, high molecular weight ones have a certain melting point:

Alcohol ethyl acetate

Ethyl (characteristic smell)

Methodology: 0.5 ml of acetic acid, 1 ml of concentrated sulfuric acid are added to 2 ml of ethyl alcohol 95% and heated to a boil - a characteristic smell of ethyl acetate is felt.

2.5.2. Oxidation reactions

Alcohols are oxidized to aldehydes by adding oxidizing agents (potassium dichromate, iodine).

Overall reaction equation:

iodoform

(yellow sediment)

Methodology: 0.5 ml of ethyl alcohol 95% is mixed with 5 ml of sodium hydroxide solution, 2 ml of 0.1 M iodine solution are added - a yellow precipitate of iodoform gradually precipitates, which also has a characteristic odor.

2.5.3. Reactions for the formation of chelate compounds (polyhydric alcohols)

Polyhydric alcohols (glycerol, etc.) form blue chelate compounds with a solution of copper sulfate and in an alkaline medium:

glycerine blue intense blue

precipitate color solution

Methodology: 1-2 ml of sodium hydroxide solution is added to 5 ml of copper sulfate solution until a precipitate of copper (II) hydroxide is formed. Then add a solution of glycerin until the precipitate dissolves. The solution turns intense blue.

2.6 IDENTIFICATION OF PHENOLIC HYDROXYL

Medicinal products containing phenolic hydroxyl:

a) Phenol b) Resorcinol

c) Sinestrol

d) Salicylic acid e) Paracetamol

2.6.1. Reaction with iron (III) chloride

Phenols in a neutral medium in aqueous or alcoholic solutions form salts with iron (III) chloride, colored blue-violet (monatomic), blue (resorcinol), green (pyrocatechol) and red (phloroglucinol). This is due to the formation of cations C 6 H 5 OFe 2+, C 6 H 4 O 2 Fe +, etc.

Methodology: to 1 ml of an aqueous or alcoholic solution of the test substance (phenol 0.1:10, resorcinol 0.1:10, sodium salicylate 0.01:10) add from 1 to 5 drops of iron (III) chloride solution. Characteristic coloration is observed.

2.6.2. Oxidation reactions (indophenol test)

a) Reaction with chloramine

When phenols interact with chloramine and ammonia, indophenol is formed, which is colored in various colors: blue-green (phenol), brownish-yellow (resorcinol), etc.

Methodology: 0.05 g of the test substance (phenol, resorcinol) is dissolved in 0.5 ml of chloramine solution, 0.5 ml of ammonia solution is added. The mixture is heated in a boiling water bath. Staining is observed.

b) Lieberman's nitrosoreaction

The colored product (red, green, red-brown) is formed by phenols, in which ortho- and pair-provisions have no substitutes.

Methodology: a grain of a substance (phenol, resorcinol, thymol, salicylic acid) is placed in a porcelain cup and moistened with 2-3 drops of a 1% solution of sodium nitrite in concentrated sulfuric acid. Coloring is observed, which changes with the addition of sodium hydroxide.

in) Substitution reactions (with bromine water and nitric acid)

The reactions are based on the ability of phenols to be brominated and nitrated due to the replacement of a mobile hydrogen atom in ortho- and pair-provisions. The bromo derivatives precipitate as a white precipitate, while the nitro derivatives are yellow.

resorcinol white precipitate

yellow staining

Methodology: bromine water is added dropwise to 1 ml of a solution of a substance (phenol, resorcinol, thymol). A white precipitate forms. When adding 1-2 ml of dilute nitric acid, a yellow color gradually appears.

2.7. IDENTIFICATION OF THE ALDEHYDE GROUP

Medicinal substances containing an aldehyde group

a) formaldehyde b) glucose

2.7.1. Redox reactions

Aldehydes are easily oxidized to acids and their salts (if the reactions proceed in an alkaline medium). If complex salts of heavy metals (Ag, Cu, Hg) are used as oxidizing agents, then as a result of the reaction, a precipitate of metal (silver, mercury) or metal oxide (copper (I) oxide) precipitates.

a) reaction with ammonia solution of silver nitrate

Methodology: 10-12 drops of ammonia solution and 2-3 drops of a substance solution (formaldehyde, glucose) are added to 2 ml of silver nitrate solution, heated in a water bath at a temperature of 50-60 ° C. Metallic silver is released in the form of a mirror or a gray precipitate.

b) reaction with Fehling's reagent

red precipitate

Methodology: 2 ml of Fehling's reagent is added to 1 ml of an aldehyde (formaldehyde, glucose) solution containing 0.01-0.02 g of the substance, heated to a boil, a brick-red precipitate of copper oxide precipitates.

2.8. IDENTIFICATION OF THE ESTER GROUP

Medicinal substances containing an ester group:

a) Acetylsalicylic acid b) Novocaine

c) Anestezin d) Cortisone acetate

2.8.1. Reactions of acid or alkaline hydrolysis

Medicinal substances containing an ester group in their structure are subjected to acid or alkaline hydrolysis, followed by the identification of acids (or salts) and alcohols:

acetylsalicylic acid

acetic acid

salicylic acid

(white precipitate)

purple staining

Methodology: 5 ml of sodium hydroxide solution is added to 0.01 g of salicylic acid and heated to a boil. After cooling, sulfuric acid is added to the solution until a precipitate forms. Then 2-3 drops of a solution of ferric chloride are added, a purple color appears.

2.8.2. hydroxam test.

The reaction is based on alkaline ester hydrolysis. During hydrolysis in an alkaline medium in the presence of hydroxylamine hydrochloride, hydroxamic acids are formed, which, with iron (III) salts, give red or red-violet iron hydroxamates. Copper(II) hydroxamates are green precipitates.

hydroxylamine hydrochloride

hydroxamic acid

iron(III) hydroxamate

anestezin hydroxylamine hydroxamic acid

iron(III) hydroxamate

Methodology: 0.02 g of the substance (acetylsalicylic acid, novocaine, anestezin, etc.) is dissolved in 3 ml of ethyl alcohol 95%, 1 ml of an alkaline solution of hydroxylamine is added, shaken, heated in a boiling water bath for 5 minutes. Then add 2 ml of dilute hydrochloric acid, 0.5 ml of 10% solution of iron (III) chloride. A red or red-violet color appears.

2.9. LACTONE DETECTION

Medicinal substances containing a lactone group:

a) Pilocarpine hydrochloride

The lactone group is an internal ester. The lactone group can be determined using the hydroxam test.

2.10. IDENTIFICATION OF THE KETO GROUP

Medicinal substances containing a keto group:

a) Camphor b) Cortisone acetate

Ketones are less reactive than aldehydes due to the lack of a mobile hydrogen atom, so oxidation takes place under harsh conditions. Ketones readily condense with hydroxylamine hydrochloride and hydrazines. Oximes or hydrazones (precipitates or colored compounds) are formed.

camphor oxime (white precipitate)

phenylhydrazine sulfate phenylhydrazone

(yellow coloration)

Methodology: 0.1 g of a medicinal substance (camphor, bromcamphor, testosterone) is dissolved in 3 ml of ethyl alcohol 95%, 1 ml of a solution of phenylhydrazine sulfate or an alkaline solution of hydroxylamine is added. The appearance of a precipitate or a colored solution is observed.

2.11. IDENTIFICATION OF THE CARBOXY GROUP

Medicinal substances containing a carboxyl group:

a) Benzoic acid b) Salicylic acid

c) Nicotinic acid

The carboxyl group easily reacts due to the mobile hydrogen atom. There are basically two types of reactions:

a) formation of esters with alcohols(see section 5.1.5);

b) formation of complex salts by heavy metal ions

(Fe, Ag, Cu, Co, Hg, etc.). This creates:

Silver salts, white

Gray mercury salts

Salts of iron (III) pinkish-yellow color,

Salts of copper (II) blue or blue,

Lilac or pink cobalt salts.

The following is the reaction with copper(II) acetate:

nicotinic acid blue precipitate

Methodology: to 5 ml of a warm solution of nicotinic acid (1:100), 1 ml of a solution of acetate or copper sulfate is added, a blue precipitate forms.

2.12. IDENTIFICATION OF A SIMPLE ETHER GROUP

Medicinal substances containing a simple ether group:

a) Diphenhydramine b) Diethyl ether

Ethers have the ability to form oxonium salts with concentrated sulfuric acid, which are colored orange.

Methodology: 3-4 drops of concentrated sulfuric acid are applied to a watch glass or a porcelain cup and 0.05 g of a medicinal substance (diphenhydramine, etc.) is added. A yellow-orange color appears, gradually turning into brick red. When water is added, the color disappears.

For diethyl ether, the reaction with sulfuric acid will not be performed due to the formation of explosive substances.

2.13. IDENTIFICATION OF PRIMARY AROMATIC

AMINO GROUPS

Medicinal substances containing a primary aromatic amino group:

a) Anestezin

b) Novocaine

Aromatic amines are weak bases, since the lone electron pair of nitrogen is shifted towards the benzene nucleus. As a result, the ability of the nitrogen atom to attach a proton is reduced.

2.13.1. Azo dye formation reaction

The reaction is based on the ability of the primary aromatic amino group to form diazonium salts in an acidic medium. When a diazonium salt is added to an alkaline solution of β-naphthol, a red-orange, red or crimson color appears (azo dye). This reaction is given by local anesthetics, sulfamides, etc.

diazonium salt

azo dye

Methodology: 0.05 g of a substance (anesthesin, novocaine, streptocide, etc.) is dissolved in 1 ml of dilute hydrochloric acid, cooled in ice, 2 ml of 1% sodium nitrite solution are added. The resulting solution is added to 1 ml of an alkaline solution of β-naphthol containing 0.5 g of sodium acetate.

A red-orange, red or crimson color or an orange precipitate appears.

2.13.2. Oxidation reactions

Primary aromatic amines are easily oxidized even by atmospheric oxygen, forming colored oxidation products. Bleach, chloramine, hydrogen peroxide, iron (III) chloride, potassium dichromate, etc. are also used as oxidizing agents.

Methodology: 0.05-0.1 g of a substance (anesthesin, novocaine, streptocide, etc.) is dissolved in 1 ml of sodium hydroxide. To the resulting solution add 6-8 drops of chloramine and 6 drops of a 1% phenol solution. As it is heated in a boiling water bath, a color appears (blue, blue-green, yellow-green, yellow, yellow-orange).

2.13.3. Lignin test

This is a type of condensation reaction of a primary aromatic amino group with aldehydes in an acidic medium. It is made on wood or newsprint.

Aromatic aldehydes contained in lignin ( P-hydroxy-bezaldehyde, lilac aldehyde, vanillin - depending on the type of lignin) interact with primary aromatic amines. Forming Schiff bases.

Methodology: several crystals of the substance are placed on lignin (newsprint), 1-2 drops of hydrochloric acid, diluted. An orange-yellow color appears.

2.14. IDENTIFICATION OF THE PRIMARY ALIPHATIC

AMINO GROUPS

Medicinal substances containing a primary aliphatic amino group:

a) Glutamic acid b) γ-Aminobutyric acid

2.14.1. Ninhydrin test

Primary aliphatic amines are oxidized by ninhydrin when heated. Ninhydrin is a stable hydrate of 1,2,3-trioxyhydrindane:

Both equilibrium forms react:

Schiff's base 2-amino-1,3-dioxoindane

blue-violet coloration

Methodology: 0.02 g of the substance (glutamic acid, aminocaproic acid and other amino acids and primary aliphatic amines) is dissolved when heated in 1 ml of water, 5-6 drops of ninhydrin solution are added and heated, a purple color appears.

2.15. IDENTIFICATION OF THE SECONDARY AMINE GROUP

Medicinal substances containing a secondary amino group:

a) Dikain b) Piperazine

Medicinal substances containing a secondary amino group form precipitates of white, greenish-brown colors as a result of reaction with sodium nitrite in an acidic medium:

nitrosamine

Methodology: 0.02 g of the medicinal substance (dicaine, piperazine) is dissolved in 1 ml of water, 1 ml of sodium nitrite solution mixed with 3 drops of hydrochloric acid is added. A precipitate falls out.

2.16. IDENTIFICATION OF THE TERTIARY AMINO GROUP

Medicinal substances containing a tertiary amino group:

a) Novocaine

b) Diphenhydramine

Medicinal substances that have a tertiary amino group in their structure have basic properties, and also exhibit strong reducing properties. Therefore, they are easily oxidized to form colored products. For this, the following reagents are used:

a) concentrated nitric acid;

b) concentrated sulfuric acid;

c) Erdmann's reagent (a mixture of concentrated acids - sulfuric and nitric);

d) Mandelin's reagent (solution of (NH 4) 2 VO 3 in sulfuric acid);

e) Frede's reagent (solution of (NH 4) 2 MoO 3 in sulfuric acid);

f) Brand's reagent (a solution of formaldehyde in sulfuric acid).

Methodology: 0.005 g of a substance (papaverine hydrochloride, reserpine, etc.) is placed on a Petri dish in the form of a powder and 1-2 drops of the reagent are added. Observe the appearance of the corresponding color.

2.17. IDENTIFICATION OF THE AMIDE GROUP.

Medicinal substances containing an amide and a substituted amide group:

a) Nicotinamide b) Nicotinic diethylamide

2.17.1. Alkaline hydrolysis

Medicinal substances containing an amide (nicotinamide) and a substituted amide group (ftivizide, fthalazol, purine alkaloids, nicotinic acid diethylamide), when heated in an alkaline medium, are hydrolyzed to form ammonia or amines and acid salts:

Methodology: 0.1 g of the substance is shaken in water, 0.5 ml of 1 M sodium hydroxide solution is added and heated. There is a smell of released ammonia or amine.

2.18. IDENTIFICATION OF THE AROMATIC NITRO GROUP

Medicinal substances containing an aromatic nitro group:

a) Levomycetin b) Metronilazole

2.18.1. Recovery reactions

Preparations containing an aromatic nitro group (levomycetin, etc.) are identified using the reduction reaction of the nitro group to the amino group, then the azo dye formation reaction is carried out:

Methodology: to 0.01 g of levomycetin add 2 ml of dilute hydrochloric acid solution and 0.1 g of zinc dust, heat in a boiling water bath for 2-3 minutes, filter after cooling. Add 1 ml of 0.1 M sodium nitrate solution to the filtrate, mix well and pour the contents of the tube into 1 ml of freshly prepared β-naphthol solution. A red color appears.

2.19. IDENTIFICATION OF THE SULFHYDRIL GROUP

Medicinal substances containing a sulfhydryl group:

a) Cysteine ​​b) Mercazolil

Organic medicinal substances containing a sulfhydryl (-SH) group (cysteine, mercazolil, mercaptopuril, etc.) form precipitates with salts of heavy metals (Ag, Hg, Co, Cu) - mercaptides (gray, white, green, etc. colors) . This is due to the presence of a mobile hydrogen atom:

Methodology: 0.01 g of the medicinal substance is dissolved in 1 ml of water, 2 drops of silver nitrate solution are added, a white precipitate is formed, insoluble in water and nitric acid.

2.20. IDENTIFICATION OF THE SULFAMIDE GROUP

Medicinal substances containing a sulfa group:

a) Sulfacyl sodium b) Sulfadimethoxine

c) Phthalazole

2.20.1. Salt formation reaction with heavy metals

A large group of medicinal substances that have a sulfamide group in the molecule exhibits acidic properties. In a weakly alkaline environment, these substances form precipitates of various colors with salts of iron (III), copper (II) and cobalt:

norsulfazole

Methodology: 0.1 g of sodium sulfacyl is dissolved in 3 ml of water, 1 ml of copper sulfate solution is added, a bluish-green precipitate is formed, which does not change upon standing (unlike other sulfonamides).

Methodology: 0.1 g of sulfadimesine is shaken with 3 ml of 0.1 M sodium hydroxide solution for 1-2 minutes and filtered, 1 ml of copper sulfate solution is added to the filtrate. A yellowish-green precipitate is formed, which quickly turns brown (unlike other sulfonamides).

The identification reactions of other sulfonamides are carried out similarly. The color of the precipitate formed in norsulfazol is dirty violet, in etazol it is grassy green, turning into black.

2.20.2. Mineralization reaction

Substances having a sulfamide group are mineralized by boiling in concentrated nitric acid to sulfuric acid, which is detected by the precipitation of a white precipitate after adding a solution of barium chloride:

Methodology: 0.1 g of the substance (sulfanilamide) is carefully (under draft) boiled for 5-10 minutes in 5 ml of concentrated nitric acid. Then the solution is cooled, carefully poured into 5 ml of water, stirred and a solution of barium chloride is added. A white precipitate falls out.

2.21. IDENTIFICATION OF ANIONS OF ORGANIC ACIDS

Medicinal substances containing acetate ion:

a) Potassium acetate b) Retinol acetate

c) Tocopherol acetate

d) Cortisone acetate

Medicinal substances that are esters of alcohols and acetic acid (retinol acetate, tocopherol acetate, cortisone acetate, etc.) are hydrolyzed when heated in an alkaline or acidic medium to form alcohol and acetic acid or sodium acetate:

2.21.1. Acetic ethyl ester formation reaction

Acetates and acetic acid interact with 95% ethyl alcohol in the presence of concentrated sulfuric acid to form ethyl acetate:

Methodology: 2 ml of an acetate solution is heated with an equal amount of concentrated sulfuric acid and 0.5 ml of 95 5 ethyl alcohol, the smell of ethyl acetate is felt.

2.21.2.

Acetates in a neutral medium interact with a solution of iron (III) chloride to form a complex red salt.

Methodology: 0.2 ml of a solution of iron (III) chloride is added to 2 ml of a neutral solution of acetate, a red-brown color appears, which disappears when diluted mineral acids are added.

Medicinal substances containing benzoate ion:

a) Benzoic acid b) Sodium benzoate

2.21.3. The reaction of formation of a complex salt of iron (III)

Medicinal substances containing benzoate ion, benzoic acid form a complex salt with a solution of iron (III) chloride:

Methodology: 0.2 ml of a solution of iron (III) chloride is added to 2 ml of a neutral solution of benzoate, a pinkish-yellow precipitate is formed, soluble in ether.

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 ».

"Dry" 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 some 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		Group reagent	Solubility of compounds
	Ag + , Pb 2+ , Hg 2 2+		Chlorides are insoluble in water
	Ca2+, Sr2+, Ba2+		Sulfates are insoluble in water
	Zn 2+ , Al 3+ , Cr 3+ , Sn 2+ , Si 4+ , ​​As		Hydroxides are amphoteric, soluble in excess alkali
	Mg 2+ , Mn 2+ , Fe 2+ , Fe 3+ , Bi 3+ , Sb 3+ , Sb 5+		Hydroxides are insoluble in excess NaOH or NH 3
Group number		Group reagent	Solubility of compounds
	Co 2+ , Ni 2+ , Cu 2+ , Cd 2+ , Hg 2+		Hydroxides dissolve in excess NH 3 with the formation of complex compounds
	Na + , K + , NH 4 +		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
Aldehyde		a) 2,4 - dinitrophenylhydrozide b) hydroxylamine hydrochloride c) sodium hydrogen sulfate
		a) nitrous acid b) benzenesulfonyl chloride
aromatic hydrocarbon		Azoxybenzene and aluminum chloride
		See aldehyde
unsaturated hydrocarbon	C \u003d C - - C ≡ C -	a) KMnO 4 solution b) Br 2 solution in CCL 4
Nitro compound		a) Fe (OH) 2 (Mohr's salt + KOH) b) zinc dust + NH 4 Cl c) 20% NaOH solution
		a) (NH 4) 2 b) ZnCl 2 solution in HCl c) iodic acid
		a) FeCl 3 in pyridine b) bromine water
Ether is simple		a) hydroiodic acid b) bromine water
Ether complex		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.

Functional analysis determines the type of functional group. For example, a reaction with (NH 4) 2 can detect alcohol, and with a KMnO 4 solution, primary, secondary and tertiary alcohols can be distinguished. Primary KMnO 4 oxidizes to aldehydes, discoloring, secondary oxidizes to ketones, forming MnO 2, and does not react with tertiary ones (Table 1.3.2).

Structural analysis establishes the structural formula of an organic substance or its individual structural elements (double and triple bonds, cycles, and so on).

Molecular analysis establishes the entire substance. For example, phenol can be detected by reaction with FeCl 3 in pyridine. More often, molecular analysis is reduced to establishing the complete composition of a compound on the basis of data on the elemental, functional, and structural composition of the substance. At present, molecular analysis is carried out mainly by instrumental methods.

When calculating the results of the analysis, it is necessary to perform the calculations very carefully. A mathematical error made in numerical values ​​is tantamount to an error in analysis.

Numerical values ​​are divided into exact and approximate. Accurate, for example, can include the number of analyzes performed, the serial number of the element in the periodic table, approximate - the measured values ​​of mass or volume.

Significant digits of an approximate number are all its digits, except for zeros to the left of the decimal point and zeros to the right after the decimal point. Zeros in the middle of a number are significant. For example, in the number 427.205 - 6 significant digits; 0.00365 - 3 significant figures; 244.00 - 3 significant figures.

The accuracy of calculations is determined by GOST, OST or TU for analysis. If the calculation error is not specified in advance, then it should be borne in mind that that the concentration is calculated up to the 4th significant figure after the decimal point, the mass - up to the 4th decimal place after the decimal point, the mass fraction (percentage) - up to hundredths.

Each analysis result cannot be more accurate than the measuring instruments allow (therefore, in the mass expressed in grams, there cannot be more than 4-5 decimal places, i.e. more than the accuracy of the analytical balance 10 -4 -10 -5 g) .

Extra numbers are rounded off according to the following rules.

1. The last digit, if it is  4, is discarded, if  5, add one to the previous one, if it is 5, and there is an even number in front of it, then add one to the previous one, and if odd, then subtract (for example, 12.465  12, 46; 12.475  12.48).

2. In the sums and differences of approximate numbers, as many decimal places are retained as there were in the number with the smallest number of them, and when dividing and multiplying, as much as is required for a given measurand (for example, when calculating the mass using the formula

Although V is measured to hundredths, the result should be calculated to 10 -4 -10 -5 g).

3. When raising to a power, as a result, take as many significant digits as there were in the number being raised to a power.

4. In intermediate results, take one decimal digit more than according to the rounding rules, and to evaluate the order of calculations, round all numbers to the first digit.

Mathematical processing of analysis results

At any of the listed stages of quantitative analysis, errors can be made and, as a rule, errors are allowed, therefore, the fewer stages an analysis has, the more accurate its results.

error measurement refers to the deviation of the measurement result x i from the true value of the measured quantity .

Difference х i -  =∆х i called absolute error , and attitude (∆х i /)100% called relative error .

The errors of the results of quantitative analysis are divided into gross (misses), systematic and random . Based on them, the quality of the obtained analysis results is assessed. Quality parameters are their right, accuracy, reproducibility and reliability.

The result of the analysis is considered correct , if it has no gross and systematic error, and if, in addition, the random error is minimized, then accurate, corresponding to the truth. To obtain accurate measurement results, quantitative determinations are repeated several times (usually odd).

Gross errors ( misses) are those that lead to a sharp difference in the result of a repeated measurement from the rest. The causes of misses are gross operational errors of the analyst (for example, the loss of part of the sediment during its filtering or weighing, incorrect calculation or recording of the result). Misses are identified among a series of repeated measurements, usually using Q-criteria. To calculate it, the results are arranged in a row in ascending order: x 1, x 2, x 3,…x n-1, x n. Doubtful is usually the first or last result in this row.

The Q-criterion is calculated as the ratio of the absolute value of the difference between the questionable result and the one closest to it in the series to the difference between the last and the first in the series. Difference x n- x 1 called range of variation.

For example, if the last result in a row is doubtful, then

To identify a miss, the Q calculated for it is compared with the tabular critical value Q table given in analytical reference books. If Q  Q table, then the questionable result is excluded from consideration, considering it a miss. Mistakes must be identified and corrected.

Systematic errors are those that lead to a deviation of the results of repeated measurements by the same positive or negative value from the true value. They can be caused by incorrect calibration of measuring devices and instruments, impurities in the reagents used, incorrect actions (for example, the choice of an indicator) or the individual characteristics of the analyst (for example, vision). Systematic errors can and should be eliminated. For this use:

1) obtaining the results of quantitative analysis by several methods different in nature;

2) development of the analysis methodology on standard samples, i.e. materials, the content of analytes, in which is known with high accuracy;

3) the method of additions (the "introduced-found" method).

Random errors - these are those that lead to insignificant deviations of the results of repeated measurements from the true value for reasons whose occurrence cannot be clarified and taken into account (for example, voltage fluctuations in the mains, the mood of the analyst, etc.). Random errors cause scatter in the results of repeated determinations carried out under identical conditions. Scatter determines reproducibility results, i.e. obtaining the same or similar results with repeated determinations. The quantitative characteristic of reproducibility is standard deviation S, which is found by methods of mathematical statistics. For a small number of measurements (small sample) with n=1-10

elective call the set of results of repeated measurements. The results themselves are called sampling options . The totality of the results of an infinitely large number of measurements (in titration n30) called the general sample , and the standard deviation calculated from it is denoted by . The standard deviation S() shows by what average value the results of n measurements deviate from the average result x or true.

"Chemistry. Grade 10". O.S. Gabrielyan (gdz)

Qualitative analysis of organic compounds | Detection of carbon, hydrogen and halogens

Experience 1. Detection of carbon and hydrogen in an organic compound.
Work conditions:
The device was assembled as shown in Fig. 44 textbooks. Pour a pinch of sugar and a little copper oxide (II) CuO into the test tube. They put a small cotton swab in a test tube, somewhere at the level of two-thirds of it, then poured a little anhydrous copper sulphate CuSO 4 . The test tube was closed with a cork with a gas outlet tube, so that its lower end was lowered into another test tube with calcium hydroxide Ca(OH) 2 previously poured into it. Heated the test tube in the flame of a burner. We observe the release of gas bubbles from the tube, the turbidity of the lime water and the blueness of the white CuSO 4 powder.
C 12 H 22 O 11 + 24CuO → 12CO 2 + 11H 2 O + 24Cu
Ca(OH) 2 + CO 2 → CaCO 3 ↓ + H 2 O
CuSO 4 + 5H 2 O → CuSO 4 . 5H2O
Conclusion: The initial substance contains carbon and hydrogen, since carbon dioxide and water were obtained as a result of oxidation, and they were not contained in the CuO oxidizer.

Experience 2. Detection of halogens
Work conditions:
They took a copper wire, bent at the end with a loop with tongs, calcined it in a flame until a black coating of copper oxide (II) CuO formed. Then the cooled wire was dipped into a solution of chloroform and again brought into the flame of the burner. We observe the coloring of the flame in a bluish-green color, since copper salts color the flame.
5CuO + 2CHCl 3 \u003d 3CuCl 2 + 2CO 2 + H 2 O + 2Cu

>> Chemistry: Practical work No. 1. Qualitative analysis of organic compounds

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