Acid with metal is specific to these classes of compounds. During its course, the hydrogen proton is reduced and, in conjunction with the acid anion, is replaced by a metal cation. This is an example of a reaction that produces a salt, although there are several types of interactions that do not follow this principle. They proceed as redox reactions and are not accompanied by the release of hydrogen.

Principles of reactions of acids with metals

All reactions with metal lead to the formation of salts. The only exception is, perhaps, the reaction of a noble metal with aqua regia, a mixture of hydrochloric acid and any other interaction of acids with metals leads to the formation of a salt. If the acid is neither concentrated sulfuric nor nitric, then molecular hydrogen is released as a product.

But when concentrated sulfuric acid, interaction with metals proceeds according to the principle of an oxidation-reduction process. Therefore, two types of interactions between typical metals and strong inorganic acids were experimentally identified:

• interaction of metals with dilute acids;
• interaction with concentrated acid.

Reactions of the first type occur with any acid. The only exceptions are concentrated and nitric acid of any concentration. They react according to the second type and lead to the formation of salts and products of the reduction of sulfur and nitrogen.

Typical interactions of acids with metals

Metals located to the left of hydrogen in the standard electrochemical series react with other acids of varying concentrations, with the exception of nitric acid, to form a salt and release molecular hydrogen. Metals located to the right of hydrogen in the electronegativity series cannot react with the above acids and interact only with nitric acid, regardless of its concentration, with concentrated sulfuric acid and with aqua regia. This is a typical reaction between acids and metals.

Reactions of metals with concentrated sulfuric acid

Reactions with dilute nitric acid

Dilute nitric acid reacts with metals located to the left and to the right of hydrogen. During the reaction with active metals, ammonia is formed, which immediately dissolves and reacts with the nitrate anion, forming another salt. The acid reacts with medium-active metals to release molecular nitrogen. With low-active ones, the reaction proceeds with the release of divalent nitrogen oxide. Most often, several sulfur reduction products are formed in one reaction. Examples of reactions are provided in the graphical appendix below.

Reactions with concentrated nitric acid

IN in this case Nitrogen also acts as an oxidizing agent. All reactions end with the formation of a salt and the release of redox reactions. Schemes for the flow of redox reactions are proposed in the graphical appendix. In this case, the reaction with low-active elements deserves special attention. This interaction of acids with metals is nonspecific.

Reactivity of metals

Metals react with acids quite readily, although there are several inert substances. These are also elements that have a high standard electrochemical potential. There are a number of metals that are built on the basis of this indicator. It is called the electronegativity series. If the metal is to the left of hydrogen in it, then it is able to react with dilute acid.

There is only one exception: iron and aluminum, due to the formation of 3-valent oxides on their surface, cannot react with acid without heating. If the mixture is heated, the metal oxide film initially reacts, and then it itself dissolves in the acid. Metals located to the right of hydrogen in the electrochemical activity series cannot react with inorganic acid, including dilute sulfuric acid. There are two exceptions to the rule: these metals dissolve in concentrated and dilute nitric acid and aqua regia. Only rhodium, ruthenium, iridium and osmium cannot be dissolved in the latter.

RATIO OF METALS TO ACIDS

Most often in chemical practice, strong acids such as sulfuric acid are used. H 2 SO 4, hydrochloric HCl and nitrogen HNO 3 . Next, we consider the relationship of various metals to the listed acids.

Hydrochloric acid ( HCl)

Hydrochloric acid is the technical name for hydrochloric acid. It is obtained by dissolving hydrogen chloride gas in water - HCl . Due to its low solubility in water, the concentration of hydrochloric acid under normal conditions does not exceed 38%. Therefore, regardless of the concentration of hydrochloric acid, the process of dissociation of its molecules into aqueous solution is active:

HCl H + + Cl -

Hydrogen ions formed in this process H+ act as an oxidizing agent, oxidizing metals located in the activity series to the left of hydrogen . The interaction proceeds according to the following scheme:

Me + HClsalt +H 2

In this case, the salt is a metal chloride ( NiCl 2, CaCl 2, AlCl 3 ), in which the number of chloride ions corresponds to the oxidation state of the metal.

Hydrochloric acid is a weak oxidizing agent, so metals with variable valency are oxidized to lowest positive oxidation states:

Fe 0 → Fe 2+

Co 0 → Co2+

Ni 0 → Ni 2+

Cr 0 →Cr 2+

Mn 0 → Mn 2+ And etc. .

Example:

2 Al + 6 HCl → 2 AlCl 3 + 3 H 2

2│ Al 0 – 3 e- → Al 3+ - oxidation

3│2 H + + 2 e- → H 2 - recovery

Hydrochloric acid passivates lead ( Pb ). Lead passivation is caused by the formation of lead chloride, which is difficult to dissolve in water, on its surface ( II ), which protects the metal from further exposure to acid:

Pb + 2 HCl → PbCl 2 ↓ + H 2

Sulfuric acid (H 2 SO 4 )

The industry produces sulfuric acid of very high concentration (up to 98%). It is necessary to take into account the difference in the oxidizing properties of a dilute solution and concentrated sulfuric acid in relation to metals.

Dilute sulfuric acid

In a dilute aqueous solution of sulfuric acid, most of its molecules dissociate:

H 2 SO 4 H + + HSO 4 -

HSO 4 - H + + SO 4 2-

Ions produced H+ perform a function oxidizing agent .

Like hydrochloric acid, diluted sulfuric acid solution reacts only with active metals And average activity (located in the activity series up to hydrogen).

The chemical reaction proceeds according to the following scheme:

Meh+H2SO4(razb .) → salt+H2

Example:

2 Al + 3 H 2 SO 4 (dil.) → Al 2 (SO 4) 3 + 3 H 2

1│2Al 0 – 6 e- → 2Al 3+ - oxidation

3│2 H + + 2 e- → H 2 - recovery

Metals with variable valence are oxidized with a dilute solution of sulfuric acid to lowest positive oxidation states:

Fe 0 → Fe 2+

Co 0 → Co2+

Ni 0 → Ni 2+

Cr 0 → Cr 2+

Mn 0 → Mn 2+ And etc. .

Lead ( Pb ) does not dissolve in sulfuric acid (if its concentration is below 80%) , since the resulting salt PbSO4 insoluble and creates a protective film on the metal surface.

Concentrated sulfuric acid

In a concentrated solution of sulfuric acid (above 68%), most of the molecules are in undissociated condition, therefore sulfur acts as an oxidizing agent , which is in the highest oxidation state ( S+6 ). Concentrated H2SO4 oxidizes all metals whose standard electrode potential is less than the potential of the oxidizing agent - sulfate ion SO 4 2- (0.36 V). In this regard, with concentrated react with sulfuric acid and some low-reactive metals .

The process of interaction of metals with concentrated sulfuric acid in most cases proceeds according to the following scheme:

Me + H 2 SO4 (conc.)salt + water + reduction product H 2 SO 4

Recovery products sulfuric acid can contain the following sulfur compounds:

Practice has shown that when a metal reacts with concentrated sulfuric acid, a mixture of reduction products is released, consisting of H 2 S, S and SO 2. However, one of these products is formed in predominant quantities. The nature of the main product is determined metal activity : the higher the activity, the deeper the process of sulfur reduction in sulfuric acid.

The interaction of metals of varying activity with concentrated sulfuric acid can be represented by the following diagram:

Aluminum (Al ) And iron ( Fe ) do not react with cold concentrated H2SO4 , becoming covered with dense oxide films, but when heated, the reaction proceeds.

Ag , Au , Ru , Os , Rh , Ir , Pt do not react with sulfuric acid.

Concentrated sulfuric acid is strong oxidizing agent , therefore, when metals with variable valency interact with it, the latter are oxidized up to more high degrees oxidation than in the case of a dilute acid solution:

Fe 0→ Fe3+,

Cr 0→ Cr3+,

Mn 0→Mn 4+,

Sn 0→ Sn 4+

Lead ( Pb ) oxidizes to divalent state with the formation of soluble lead hydrogen sulfatePb ( HSO 4 ) 2 .

Examples:

Active metal

8 A1 + 15 H 2 SO 4 (conc.) →4A1 2 (SO 4) 3 + 12H 2 O + 3H 2 S

4│2 Al 0 – 6 e- → 2 Al 3+ - oxidation

3│ S 6+ + 8 e → S 2- - recovery

Medium activity metal

2 Cr + 4 H 2 SO 4 (conc.) → Cr 2 (SO 4) 3 + 4 H 2 O + S

1│ 2Cr 0 – 6e →2Cr 3+ - oxidation

1│ S 6+ + 6 e → S 0 - recovery

Low-active metal

2Bi + 6H 2 SO 4 (conc.) → Bi 2 (SO 4) 3 + 6H 2 O + 3SO 2

1│ 2Bi 0 – 6e → 2Bi 3+ – oxidation

3│ S 6+ + 2 e → S 4+ - recovery

Nitric acid ( HNO 3 )

The peculiarity of nitric acid is that the nitrogen included in the composition NO 3 - has the highest oxidation state +5 and therefore has strong oxidizing properties. Maximum value The electrode potential for the nitrate ion is 0.96 V, so nitric acid is a stronger oxidizing agent than sulfuric acid. The role of an oxidizing agent in the reactions of metals with nitric acid is played by N 5+ . Hence, hydrogen H 2 never stands out when metals interact with nitric acid ( regardless of concentration ). The process proceeds according to the following scheme:

Me + HNO 3 salt + water + reduction product HNO 3

Recovery Products HNO 3 :

Usually, when nitric acid reacts with a metal, a mixture of reduction products is formed, but as a rule, one of them is predominant. Which product will be the main one depends on the concentration of the acid and the activity of the metal.

Concentrated nitric acid

An acid solution with a density ofρ > 1.25 kg/m 3, which corresponds to
concentrations > 40%. Regardless of the activity of the metal, the reaction of interaction with HNO3 (conc.) proceeds according to the following scheme:

Me + HNO 3 (conc.)→ salt + water + NO 2

Noble metals do not react with concentrated nitric acid (Au , Ru , Os , Rh , Ir , Pt ), and a number of metals (Al , Ti , Cr , Fe , Co , Ni ) at low temperature passivated with concentrated nitric acid. The reaction is possible with increasing temperature; it proceeds according to the scheme presented above.

Examples

Active metal

Al + 6 HNO 3 (conc.) → Al (NO 3 ) 3 + 3 H 2 O + 3 NO 2

1│ Al 0 – 3 e → Al 3+ - oxidation

3│ N 5+ + e → N 4+ - recovery

Medium activity metal

Fe + 6 HNO 3(conc.) → Fe(NO 3) 3 + 3H 2 O + 3NO

1│ Fe 0 – 3e → Fe 3+ - oxidation

3│ N 5+ + e → N 4+ - recovery

Low-active metal

Ag + 2HNO 3 (conc.) → AgNO 3 + H 2 O + NO 2

1│ Ag 0 – e → Ag + - oxidation

1│ N 5+ + e → N 4+ - recovery

Dilute nitric acid

Recovery product nitric acid in a dilute solution depends on metal activity involved in the reaction:

Examples:

Active metal

8 Al + 30 HNO 3(dil.) → 8Al(NO 3) 3 + 9H 2 O + 3NH 4 NO 3

8│ Al 0 – 3e → Al 3+ - oxidation

3│ N 5+ + 8 e → N 3- - recovery

The ammonia released during the reduction of nitric acid immediately reacts with excess nitric acid, forming a salt - ammonium nitrate NH4NO3:

NH 3 + HNO 3 → NH 4 NO 3.

Medium activity metal

10Cr + 36HNO 3(dil.) → 10Cr(NO 3) 3 + 18H 2 O + 3N 2

10│ Cr 0 – 3 e → Cr 3+ - oxidation

3│ 2 N 5+ + 10 e → N 2 0 - recovery

Except molecular nitrogen ( N 2 ) when metals of intermediate activity interact with dilute nitric acid, they are formed in equal quantities Nitric oxide ( I) – N 2 O . In the reaction equation you need to write one of these substances .

Low-active metal

3Ag + 4HNO 3(dil.) → 3AgNO 3 + 2H 2 O + NO

3│ Ag 0 – e → Ag + - oxidation

1│ N 5+ + 3 e → N 2+ - recovery

"Aqua regia"

“Royal vodka” (previously acids were called vodkas) is a mixture of one volume of nitric acid and three to four volumes of concentrated hydrochloric acid, which has very high oxidizing activity. Such a mixture is capable of dissolving some low-active metals that do not react with nitric acid. Among them is the “king of metals” - gold. This effect of “regia vodka” is explained by the fact that nitric acid oxidizes hydrochloric acid, releasing free chlorine and forming nitrogen chloroxide ( III ), or nitrosyl chloride – NOCl:

HNO 3 + 3 HCl → Cl 2 + 2 H 2 O + NOCl

2 NOCl → 2 NO + Cl 2

Chlorine at the moment of release consists of atoms. Atomic chlorine is a strong oxidizing agent, which allows “regia vodka” to affect even the most inert “noble metals”.

The oxidation reactions of gold and platinum proceed according to the following equations:

Au + HNO 3 + 4 HCl → H + NO + 2H 2 O

3Pt + 4HNO3 + 18HCl → 3H2 + 4NO + 8H2O

For Ru, Os, Rh and Ir "Aqua regia" does not work.

E.A. Nudnova, M.V. Andryukhova

Sulfur trioxide typically appears as a colorless liquid. It can also exist in the form of ice, fibrous crystals or gas. When sulfur trioxide is exposed to air, white smoke begins to be released. It is a component of such a chemically active substance as concentrated sulfuric acid. It is a clear, colorless, oily and very aggressive liquid. It is used in the production of fertilizers, explosives, other acids, in the oil industry, in lead-acid batteries in cars.

Concentrated sulfuric acid: properties

Sulfuric acid is highly soluble in water, has a corrosive effect on metals and fabrics, and upon contact chars wood and most other materials. organic matter. Adverse health effects from inhalation may occur as a result of long-term exposure to low concentrations of the substance or short-term exposure to high concentrations.

Concentrated sulfuric acid is used to make fertilizers and other chemicals, in oil refining, in iron and steel production, and for many other purposes. Because it has a fairly high boiling point, it can be used to release more volatile acids from their salts. Concentrated sulfuric acid has strong hygroscopic properties. It is sometimes used as a drying agent to dehydrate (chemically remove water) many compounds, such as carbohydrates.

Sulfuric acid reactions

Concentrated sulfuric acid reacts with sugar in an unusual way, leaving behind a brittle, spongy black mass of carbon. A similar reaction is observed when exposed to leather, cellulose and other plant and animal fibers. When concentrated acid mixed with water, a large amount of heat is released, sufficient for instant boiling. To dilute, it should be added slowly to cold water with constant stirring to limit heat buildup. Sulfuric acid reacts with liquid, forming hydrates with pronounced properties.

physical characteristics

A colorless and odorless liquid in a diluted solution has a sour taste. Sulfuric acid is extremely aggressive when exposed to the skin and all tissues of the body, causing severe burns upon direct contact. In its pure form, H 2 SO4 is not a conductor of electricity, but the situation changes in the opposite side with the addition of water.

Some properties are that the molecular weight is 98.08. The boiling point is 327 degrees Celsius, the melting point is -2 degrees Celsius. Sulfuric acid is a strong mineral acid and one of the main products of the chemical industry due to its wide commercial applications. It forms naturally from the oxidation of sulfide materials such as iron sulfide.

The chemical properties of sulfuric acid (H 2 SO4) are manifested in various chemical reactions:

1. When interacting with alkalis, two series of salts are formed, including sulfates.
2. Reacts with carbonates and bicarbonates to form salts and carbon dioxide(CO 2).
3. It affects metals differently, depending on the temperature and degree of dilution. Cold and dilute releases hydrogen, hot and concentrated releases SO 2 emissions.
4. A solution of H 2 SO4 (concentrated sulfuric acid) decomposes into sulfur trioxide (SO 3) and water (H 2 O) when boiled. Chemical properties also include the role of a strong oxidizing agent.

Fire danger

Sulfuric acid is highly reactive to ignite finely dispersed combustible materials upon contact. When heated, highly toxic gases begin to be released. It is explosive and incompatible with a large number of substances. At elevated temperatures and pressures, quite aggressive chemical changes and deformations can occur. May react violently with water and other liquids, causing splashing.

Health Hazard

Sulfuric acid corrodes all body tissues. Inhalation of vapors may cause serious lung damage. Damage to the mucous membrane of the eyes can lead to complete loss of vision. Contact with skin may cause severe necrosis. Even a few drops can be fatal if the acid gains access to the trachea. Chronic exposure can cause tracheobronchitis, stomatitis, conjunctivitis, gastritis. Gastric perforation and peritonitis may occur, accompanied by circulatory collapse. Sulfuric acid is very caustic and should be handled with extreme care. Signs and symptoms of exposure can be severe and include drooling, extreme thirst, difficulty swallowing, pain, shock and burns. Vomit is usually the color of ground coffee. Acute inhalation exposure may result in sneezing, hoarseness, choking, laryngitis, shortness of breath, airway irritation and chest pain. Bleeding from the nose and gums, pulmonary edema, chronic bronchitis and pneumonia may also occur. Skin exposure may result in severe painful burns and dermatitis.

First aid

1. Place victims in fresh air. Emergency services personnel should avoid exposure to sulfuric acid.
2. Estimate vital statistics including heart rate and breathing rate. If a pulse is not detected, perform resuscitation measures depending on the additional injuries received. If breathing is difficult, provide respiratory support.
3. Remove soiled clothing as soon as possible.
4. In case of contact with eyes, rinse with warm water for at least 15 minutes; on skin, wash with soap and water.
5. If you inhale toxic fumes, you should rinse your mouth with plenty of water; you should not drink or induce vomiting yourself.
6. Transport victims to a medical facility.

OVRs are specially highlighted in color in the article. Pay special attention to them. These equations may appear on the Unified State Exam.

Dilute sulfuric acid behaves like other acids, hiding its oxidative capabilities:

And one more thing to remember about dilute sulfuric acid: she does not react with lead. A piece of lead thrown into dilute H2SO4 becomes covered with a layer of insoluble (see solubility table) lead sulfate and the reaction immediately stops.

Oxidizing properties of sulfuric acid

– heavy oily liquid, non-volatile, tasteless and odorless

Due to sulfur in the oxidation state +6 (higher), sulfuric acid acquires strong oxidizing properties.

Rule for task 24 (old A24) when preparing sulfuric acid solutions You should never pour water into it. Concentrated sulfuric acid should be poured into the water in a thin stream, stirring constantly.

Reaction of concentrated sulfuric acid with metals

These reactions are strictly standardized and follow the following scheme:

H2SO4(conc.) + metal → metal sulfate + H2O + reduced sulfur product.

There are two nuances:

1) Aluminum, iron And chromium They do not react with H2SO4 (conc.) under normal conditions due to passivation. Needs to be heated.

2) C platinum And gold H2SO4 (conc) does not react at all.

Sulfur V concentrated sulfuric acid- oxidizer

• This means that it will recover itself;
• the degree of oxidation to which sulfur is reduced depends on the metal.

Let's consider sulfur oxidation state diagram:

• Before -2 sulfur can only be reduced by very active metals - in a series of voltages up to and including aluminum.

The reactions will go like this:

8Li+5H 2 SO 4( conc. .) → 4Li 2 SO 4 + 4H 2 O+H 2 S

4Mg + 5H 2 SO 4( conc. .) → 4MgSO 4 + 4H 2 O+H 2 S

8Al + 15H 2 SO 4( conc. .) (t)→ 4Al 2 (SO 4 ) 3 +12H 2 O+3H 2 S

• upon interaction of H2SO4 (conc) with metals in a series of voltages after aluminum, but before iron, that is, with metals with average activity, sulfur is reduced to 0 :

3Mn + 4H 2 SO 4( conc. .) → 3MnSO 4 + 4H 2 O+S↓

2Cr + 4H 2 SO 4( conc. .) (t)→Cr 2 (SO 4 ) 3 + 4H 2 O+S↓

3Zn + 4H 2 SO 4( conc. .) → 3ZnSO 4 + 4H 2 O+S↓

• all other metals starting with hardware in a number of voltages (including those after hydrogen, except for gold and platinum, of course), they can only reduce sulfur to +4. Since these are low-active metals:

2 Fe + 6 H 2 SO 4(conc.) ( t)→ Fe 2 ( SO 4 ) 3 + 6 H 2 O + 3 SO 2

(note that iron oxidizes to +3, the highest possible oxidation state, since it is a strong oxidizing agent)

Cu+2H 2 SO 4( conc. .) → CuSO 4 + 2H 2 O+SO 2

2Ag + 2H 2 SO 4( conc. .) → Ag 2 SO 4 + 2H 2 O+SO 2

Of course, everything is relative. The depth of recovery will depend on many factors: acid concentration (90%, 80%, 60%), temperature, etc. Therefore, it is impossible to predict products completely accurately. The above table also has its own approximate percentage, but you can use it. It is also necessary to remember that in the Unified State Examination, when the product of reduced sulfur is not indicated and the metal is not particularly active, then, most likely, the compilers mean SO 2. You need to look at the situation and look for clues in the conditions.

SO 2 - this is generally a common product of ORR with the participation of conc. sulfuric acid.

H2SO4 (conc) oxidizes some nonmetals(which exhibit reducing properties), as a rule, to a maximum - the highest degree of oxidation (an oxide of this non-metal is formed). In this case, sulfur is also reduced to SO 2:

C+2H 2 SO 4( conc. .) → CO 2 + 2H 2 O+2SO 2

2P+5H 2 SO 4( conc. .) → P 2 O 5 +5H 2 O+5SO 2

Freshly formed phosphorus oxide (V) reacts with water to produce orthophosphoric acid. Therefore, the reaction is recorded immediately:

2P+5H 2 SO 4( conc. ) → 2H 3 P.O. 4 + 2H 2 O+5SO 2

The same thing with boron, it turns into orthoboric acid:

2B+3H 2 SO 4( conc. ) → 2H 3 B.O. 3 +3SO 2

The interaction of sulfur with an oxidation state of +6 (in sulfuric acid) with “other” sulfur (located in a different compound) is very interesting. Within the framework of the Unified State Examination, the interaction of H2SO4 (conc) is considered with sulfur (a simple substance) and hydrogen sulfide.

Let's start with interaction sulfur (a simple substance) with concentrated sulfuric acid. IN simple matter oxidation state 0, in acid +6. In this ORR, sulfur +6 will oxidize sulfur 0. Let's look at the diagram of the oxidation states of sulfur:

Sulfur 0 will oxidize, and sulfur +6 will be reduced, that is, lower the oxidation state. Sulfur dioxide will be released:

2 H 2 SO 4(conc.) + S → 3 SO 2 + 2 H 2 O

But in the case of hydrogen sulfide:

Both sulfur (a simple substance) and sulfur dioxide are formed:

H 2 SO 4( conc. .) +H 2 S → S↓ + SO 2 + 2H 2 O

This principle can often help in determining the product of ORR, where the oxidizing and reducing agent are the same element, in different degrees oxidation. The oxidizing agent and the reducing agent “meet each other halfway” according to the oxidation state diagram.

H2SO4 (conc), one way or another, interacts with halides. Only here you need to understand that fluorine and chlorine are “themselves with a mustache” and ORR does not occur with fluorides and chlorides, undergoes a conventional ion exchange process during which hydrogen halide gas is formed:

CaCl 2 + H 2 SO 4 (conc.) → CaSO 4 + 2HCl

CaF 2 + H 2 SO 4 (conc.) → CaSO 4 + 2HF

But the halogens in the composition of bromides and iodides (as well as in the composition of the corresponding hydrogen halides) are oxidized to free halogens. Only sulfur is reduced in different ways: iodide is a stronger reducing agent than bromide. Therefore, iodide reduces sulfur to hydrogen sulfide, and bromide to sulfur dioxide:

2H 2 SO 4( conc. .) + 2NaBr → Na 2 SO 4 + 2H 2 O+SO 2 +Br 2

H 2 SO 4( conc. .) + 2HBr → 2H 2 O+SO 2 +Br 2

5H 2 SO 4( conc. .) + 8NaI → 4Na 2 SO 4 + 4H 2 O+H 2 S+4I 2 ↓

H 2 SO 4( conc. .) + 8HI → 4H 2 O+H 2 S+4I 2 ↓

Hydrogen chloride and hydrogen fluoride (as well as their salts) are resistant to the oxidizing action of H2SO4 (conc.).

And finally, the last thing: this is unique for concentrated sulfuric acid, no one else can do this. She has water-removing property.

This allows concentrated sulfuric acid to be used in a variety of ways:

First, drying of substances. Concentrated sulfuric acid removes water from the substance and it “becomes dry.”

Secondly, a catalyst in reactions in which water is eliminated (for example, dehydration and esterification):

H 3 C–COOH + HO–CH 3 (H 2 SO 4 (conc.)) → H 3 C–C(O)–O–CH 3 + H 2 O

H 3 C–CH 2 –OH (H 2 SO 4 (conc.)) → H 2 C =CH 2 + H 2 O

Physical properties of sulfuric acid:
Heavy oily liquid (“oil of vitriol”);
density 1.84 g/cm3; non-volatile, highly soluble in water - with strong heating; t°pl. = 10.3°C, t°boil. = 296°C, very hygroscopic, has water-removing properties (charring of paper, wood, sugar).

The heat of hydration is so great that the mixture can boil, splash and cause burns. Therefore, it is necessary to add acid to water, and not vice versa, since when water is added to acid, lighter water will end up on the surface of the acid, where all the heat generated will be concentrated.

Industrial production of sulfuric acid (contact method):

1) 4FeS 2 + 11O 2 → 2Fe 2 O 3 + 8SO 2

2) 2SO 2 + O 2 V 2 O 5 → 2SO 3

3) nSO 3 + H 2 SO 4 → H 2 SO 4 nSO 3 (oleum)

Crushed, purified, wet pyrite (sulfur pyrite) is poured into the kiln on top for firing in " fluidized bed". Air enriched with oxygen is passed from below (counterflow principle).
Furnace gas comes out of the furnace, the composition of which is: SO 2, O 2, water vapor (the pyrite was wet) and tiny particles of cinder (iron oxide). The gas is purified from impurities of solid particles (in a cyclone and electric precipitator) and water vapor (in a drying tower).
In a contact apparatus, sulfur dioxide is oxidized using a catalyst V 2 O 5 (vanadium pentoxide) to increase the reaction rate. The process of oxidation of one oxide to another is reversible. Therefore, optimal conditions for a direct reaction are selected - increased pressure (since direct reaction is underway with a decrease in total volume) and a temperature not higher than 500 C (since the reaction is exothermic).

In the absorption tower, sulfur oxide (VI) is absorbed by concentrated sulfuric acid.
Absorption by water is not used, because sulfur oxide dissolves in water with the release of a large amount of heat, so the resulting sulfuric acid boils and turns into steam. To prevent the formation of sulfuric acid fog, use 98% concentrated sulfuric acid. Sulfur oxide dissolves very well in such an acid, forming oleum: H 2 SO 4 nSO 3

Chemical properties of sulfuric acid:

H 2 SO 4 is a strong dibasic acid, one of the strongest mineral acids; due to its high polarity, the H – O bond is easily broken.

1) Sulfuric acid dissociates in aqueous solution , forming a hydrogen ion and an acidic residue:
H 2 SO 4 = H + + HSO 4 - ;
HSO 4 - = H + + SO 4 2- .
Summary equation:
H 2 SO 4 = 2H + + SO 4 2- .

2) Interaction of sulfuric acid with metals:
Dilute sulfuric acid dissolves only metals in the voltage series to the left of hydrogen:
Zn 0 + H 2 +1 SO 4 (diluted) → Zn +2 SO 4 + H 2

3) Reaction of sulfuric acidwith basic oxides:
CuO + H 2 SO 4 → CuSO 4 + H 2 O

4) Reaction of sulfuric acid withhydroxides:
H 2 SO 4 + 2NaOH → Na 2 SO 4 + 2H 2 O
H 2 SO 4 + Cu(OH) 2 → CuSO 4 + 2H 2 O

5) Exchange reactions with salts:
BaCl 2 + H 2 SO 4 → BaSO 4 ↓ + 2HCl
The formation of a white precipitate of BaSO 4 (insoluble in acids) is used to detect sulfuric acid and soluble sulfates ( qualitative reaction to sulfate ion).

Special properties of concentrated H 2 SO 4:

1) Concentrated sulfuric acid is strong oxidizing agent ; when interacting with metals (except Au, Pt), it is reduced to S +4 O 2, S 0 or H 2 S -2 depending on the activity of the metal. Without heating, it does not react with Fe, Al, Cr - passivation. When interacting with metals with variable valency, the latter oxidize to higher oxidation states than in the case of a dilute acid solution: Fe 0→ Fe 3+, Cr 0→ Cr 3+ , Mn 0→Mn 4+,Sn 0→ Sn 4+

Active metal

8 Al + 15 H 2 SO 4 (conc.) → 4Al 2 (SO 4) 3 + 12H 2 O + 3 H2S
4│2Al 0 – 6 e— → 2Al 3+ — oxidation
3│ S 6+ + 8e → S 2– recovery

4Mg+ 5H 2 SO 4 → 4MgSO 4 + H 2 S + 4H 2 O

Medium activity metal

2Cr + 4 H 2 SO 4 (conc.) → Cr 2 (SO 4) 3 + 4 H 2 O + S
1│ 2Cr 0 – 6e →2Cr 3+ - oxidation
1│ S 6+ + 6e → S 0 – recovery

Low-active metal

2Bi + 6H 2 SO 4 (conc.) → Bi 2 (SO 4) 3 + 6H 2 O + 3 SO 2
1│ 2Bi 0 – 6e → 2Bi 3+ – oxidation
3│ S 6+ + 2e →S 4+ - recovery

2Ag + 2H 2 SO 4 →Ag 2 SO 4 + SO 2 + 2H 2 O

2) Concentrated sulfuric acid oxidizes some non-metals, usually to the maximum oxidation state, and is itself reduced toS+4O2:

C + 2H 2 SO 4 (conc) → CO 2 + 2SO 2 + 2H 2 O

S+ 2H 2 SO 4 (conc) → 3SO 2 + 2H 2 O

2P+ 5H 2 SO 4 (conc) → 5SO 2 + 2H 3 PO 4 + 2H 2 O

3) Oxidation of complex substances:
Sulfuric acid oxidizes HI and HBr to free halogens:
2 KBr + 2H 2 SO 4 = K 2 SO 4 + SO 2 + Br 2 + 2H 2 O
2 KI + 2H 2 SO 4 = K 2 SO 4 + SO 2 + I 2 + 2H 2 O
Concentrated sulfuric acid cannot oxidize chloride ions to free chlorine, which makes it possible to obtain HCl by the exchange reaction:
NaCl + H 2 SO 4 (conc.) = NaHSO 4 + HCl

Sulfuric acid takes away chemically bound water from organic compounds containing hydroxyl groups. Dehydration of ethyl alcohol in the presence of concentrated sulfuric acid produces ethylene:
C 2 H 5 OH = C 2 H 4 + H 2 O.

The charring of sugar, cellulose, starch and other carbohydrates upon contact with sulfuric acid is also explained by their dehydration:
C 6 H 12 O 6 + 12H 2 SO 4 = 18H 2 O + 12SO 2 + 6CO 2.