Chemistry qualitative reactions table. Qualitative reactions to inorganic and organic substances (Grade 9)

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.

To determine the silver cation, you need to carry out a reaction with some kind of chloride. The interaction of Ag(+) and Cl(-) results in a white precipitate AgCl↓. Barium cations Ba2+ are found in the reaction with sulfates: Ba(2+)+SO4(2-)=BaSO4↓ (white precipitate). The opposite is also true: in order to detect chloride ions or sulfate ions in a solution, it is necessary to carry out a reaction with silver and barium salts, respectively.

To determine the Fe(2+) cations, potassium hexacyanoferrate (III) K3 is used, or rather, the complex ion (3-). The resulting dark blue precipitate of Fe32 is called "Turnbull blue". To detect iron (III) cations, potassium hexacyanoferrate (II) K4 is already taken, which, when interacting with Fe (3+), gives a dark blue precipitate Fe43 - “Prussian blue”. Fe(3+) can also be detected in the reaction with ammonium thiocyanate NH4CNS. As a result, low-dissociating iron(III) thiocyanate Fe(CNS)3 is formed, and the solution acquires a blood-red color.

An excess of hydrogen cations H + creates an acidic environment in which the colors of the indicators change accordingly: orange and purple litmus become red. In an excess of hydroxide ions OH- (alkaline medium), litmus turns blue, methyl orange turns yellow, and phenolphthalein, which is colorless in neutral and acidic media, acquires a crimson color.

To understand if there is an ammonium cation NH4 + in the solution, you need to add alkali. Upon reversible interaction with hydroxide ions, NH4+ gives ammonia NH3 and water. Ammonia has a characteristic smell, and wet litmus paper will turn blue in such a solution.

The qualitative reaction for ammonia uses HCl. During the formation of ammonium chloride HN4Cl from ammonia and hydrogen chloride, white smoke can be observed.

Carbonate and bicarbonate ions CO3(2-) and HCO3(-) can be detected by adding acid. As a result of the interaction of these ions with hydrogen cations, carbon dioxide is released and water is formed. When the resulting gas is passed through Ca(OH) lime water, since an insoluble compound is formed - calcium carbonate CaCO3↓. With further transmission of carbon dioxide, an acid salt is formed - already soluble Ca (HCO3) 2.

Reagent for the detection of sulfide ions S(2-) - soluble lead salts, which react with S(2-) to give a black precipitate PbS↓.

Ion detection with a torch

Salts of some metals, when added to the flame of the burner, color it. This property is used in qualitative analysis to detect cations of these elements. So, Ca(2+) colors the flame brick-red, Ba(2+) - yellow-green. The burning of potassium salts is accompanied by a violet flame, lithium - bright red, sodium - yellow, strontium - carmine red.

Qualitative reactions in organic chemistry

Compounds with double and triple bonds (alkenes, alkadienes, alkynes) discolor red-brown bromine water Br2 and pink solution of potassium permanganate KMnO4. Substances with two or more hydroxo groups -OH (polyhydric alcohols, monosaccharides, disaccharides) dissolve a freshly prepared blue precipitate of Cu (OH) 2 in an alkaline medium, forming a bright blue solution. Aldehydes, aldoses, and reducing disaccharides (aldehyde group) also react with copper (II) hydroxide, but brick-red Cu2O↓ precipitates here.

Phenol in a solution of iron (III) chloride forms a complex compound with FeCl3 and gives a violet color. Substances containing an aldehyde group give "silver mirror" reactions with an ammonia solution of silver oxide. When starch is added to an iodine solution, it turns purple, and peptide bonds of proteins are found in reaction with a saturated solution of copper sulfate and concentrated sodium hydroxide.

Sources:

• § Qualitative reactions in chemistry

An acid is a complex substance that can be either organic or inorganic. What they have in common is that they contain hydrogen atoms and an acidic residue. It is the latter that gives specific properties to each acid, and also a qualitative analysis is carried out on it. Any water-soluble acid dissociates (breaks down) into particles - positively charged hydrogen ions, which determine the acidic properties, and into negatively charged ions of the acid residue.

You will need

• - tripod;
• - test tubes;
• - indicator solutions;
• - silver nitrate;
• - acid solutions;
• - barium nitrate;
• - copper shavings.

Instruction

To determine what exactly is in the solution, use the indicator (paper or in solution). Add litmus to the test solution, which turns red in an acidic environment. For reliability, add another indicator - methyl orange, which will change color to pink or pink. The third indicator, namely phenolphthalein, does not change in an acidic environment, while remaining transparent. These experiments prove the presence of acid, but not the specificity of each of them.

In order to determine specifically what is in the flask, it is necessary to carry out a qualitative reaction to the residue. Sulfuric acid contains a sulfate ion, the reagent for which is a barium ion. Add to a substance containing this ion, such as barium nitrate. A white precipitate will instantly form, which is barium sulfate.

Qualitative Analysis is designed to detect individual elements or ions that make up the substance.

Analytical reactions are accompanied by an analytical effect that allows obtaining information about the presence of the element being determined. Analytical effects include: the precipitation or dissolution of a precipitate, the release of gaseous products, a change in the color of the solution, the formation of crystals of a certain shape.

To determine the presence of substances, anions, cations are used quality responses. By conducting them, you can confirm unambiguously their presence. These reactions are widely used in qualitative analysis, the purpose of which is to determine the presence of substances or ions in solutions or mixtures. Here is the minimum of qualitative reactions necessary for passing the exam.

I. Qualitative reactions to cations.

1. Hydrogen cation H +, change in the color of the indicators: red litmus, pink-red - methyl orange.

2. Ammonium ion:

NH + 4 + OH → NH 3 + H 2 O (smell or blue of wet litmus paper).

3. Fe 2+ ion:

3Fe 2+ + 2 2 ↓ (turnbull blue); Fe 2+ + 2OH \u003d Fe (OH) 2 ↓ . (greenish precipitate).

4. Fe 3+ ion:

4Fe 3+ + 3 4- → Fe 4 3 ↓ (Prussian blue);

Fe 3+ + 3CNS → Fe(CNS) 3 (blood red);

Fe 3+ + 3OH - \u003d Fe (OH) 3 ↓ (brown precipitate).

5. IonA1 3+:

Al 3+ + 3OH - → A1 (OH) 3 ↓ (white precipitate, soluble in excess alkali).

6. Ion Va 2+:

Ba 2+ + SO 4 2- → BaSO 4 ↓ . (white precipitate).

7. Ca 2+ ion:

Ca 2+ + CO 3 2- → CaCO 3 ↓ . (white precipitate).

8. Ion C 2+:

Cu 2+ + 2OH - → Сu (OH) 2 ↓ (blue precipitate).

9. Ion Ag +:

Ag + + CI - → AgCl ↓ (white curdled sediment).

10. Flame Coloring:

II. Qualitative reactions to anions.

1. Hydroxide ion: OH - : color change of indicators: litmus - blue, phenolphthalein - raspberry, methyl orange - yellow.

2. Halide ions:

F - + Ag + → no precipitate is formed;

С1 - + Ag + → AgC ↓ - white precipitate

Br - + Ag + →AgBr ↓ - yellowish white precipitate

I - + Ag + →AgI ↓ - bright yellow sediment

3. Sulfide ion:

H 2 S + Pb(NO 3) 2 → PbS ↓ + 2HNO 3 ;

CuSO 4 + H 2 S (Na 2 S) → H 2 SO 4 (Na,SO 4) + CuS ↓ (black precipitate).

4. Sulfate ion:

BaCI 2 + H,SO 4 → BaSO 4 ↓ + 2HC1; Ba 2+ + SO 4 2- \u003d BaSO 4 ↓ (white precipitate).

5. Nitrate ion:

Cu 2+ + NO 3 - + 2H + → Cu 2+ + NO 2 + H 2 O (brown gas).

6. Phosphate ion:

PO 4 3- + 3Ag + → Ag 3 PO 4 ↓ (yellow precipitate, which, unlike the AgBr precipitate, is soluble in mineral acids).

7. Chromate ion:

CrO 4 2- + Ba 2+ → BaCrO 4 ↓ . (yellow precipitate).

8. Carbonate ion, detection of CO 2:
CO 3 2- + 2H + → CO 2 + H 2 O;

CO 2 + Ca (OH) 2 → CaCO 3 + H 2 O;

CaCO 3 + CO 2 + H 2 O → Ca (HCO 3) 2.

III. Qualitative reaction to ozone:

2KI + O 3 + H 2 O → I 2 ↓ + 2KOH + O 2; KI + O 2 → does not go

The formation of iodine can be proved by the change in color of the solution in the presence of starch: a blue color occurs.

Identification of organic compounds

1. Qualitative reactions to compounds containing double and triple bonds (alkenes, alkadienes, alkynes, etc.). Discoloration of potassium permanganate:

3CH 2 \u003d CH 2 + 2KMnO 4 + 4H 2 O → 3C H 2 OH - C H 2 OH + 2MnO 2 + 2KOH;

3C H \u003d C H + 8KMpO 4 → 3KOOS-COOK + 8MnO 2 + 2KOH + 2H 2 O.

Discoloration of bromine water:

H 3 C-CH 2 -CH \u003d CH 2 + Br 2 → H 3 C-CH 2 -CH-CH 2;

CH≡CH + 2Br 2 → CHBr 2 -CHBr 2

CH 2 \u003d CH-COOH + Br 2 → CH 2 Br-CHBr-COOH.

Qualitative reactions to polyhydric alcohols, mono- and disaccharides.

Interaction with Cu (OH) 2 in the cold is qualitative reaction on polyhydric alcohols, as well as on mono- and disaccharides:

Monosaccharide (disaccharide) + Сu (OH) (blue precipitate) → blue solution:

3. Qualitative reaction to phenols.

C 6 H 5 OH + FeCl 3 → dark purple complex compound.

4. Qualitative reactions "Silver Mirror" and with a freshly prepared precipitate of Cu (OH) 2 for the aldehyde group:

CH 3 CHO + Ag 2 O (NH 3) → CH 3 COOH + 2Ag |;

HCHO + 2Ag 2 O (NH 3) → CO 2 + H 2 O + 4Ag ↓

CH 2 OH-(CHOH) 4 -CHO + Ag 2 O (NH 3) → CH 2 OH-(CHOH) 4 -COOH + 2Ag ↓ ;

CH 3 CHO + 2Сu(OH) 2 →CH 3 COOH + Cu 2 O ↓ + 2H 2 O

5. Qualitative reactions for organic acids:
CH 3 COOH: litmus red;

CH 3 COOH + Na 2 CO 3 → CH 3 COONa + H 2 O + CO 2 (gas evolution);

HCOOH: litmus red;

2HCOOH + Na 2 CO 3 → 2HCOONa + H 2 O + CO 2 (gas evolution);

HCOOH + Ag 2 O (NH 3) → CO 2 + H 2 O + 2Ag ↓

6. Qualitative reaction with iodine for starch:

(C 6 H | 0 O 5) n + I 2 → blue color.

Qualitative reactions to proteins

a) biuret reaction.

When the protein is treated with a concentrated solution of alkali and a solution of copper sulfate, a red-violet color appears, caused by the formation of a copper complex of the protein (reaction to a peptide bond);

b) xantoprotein reaction.

Under the action of concentrated nitric acid, the protein turns yellow. The reaction is associated with the presence of aromatic groups in the protein molecule, which are nitrated under mild conditions;

c) sulfhydryl reaction.

When lead (II) acetate and sodium hydroxide are added to a protein solution, a black precipitate of lead sulfide precipitates when heated, due to the presence of thiol (sulfhydryl) groups in the protein.