Hno3 is what kind of acid. Oxidative properties of nitric acid

16.10.2019

Regardless of the concentration, the oxidizing agent in nitric acid is nitrations NO, containing nitrogen in the oxidation state +5. Therefore, when metals interact with nitric acid, hydrogen is not released. Nitric acid oxidizes all metals except the most inactive (noble). In this case, salt, water and nitrogen reduction products (+5) are formed: NH−3 4 NO 3, N 2, N 2 O, NO, НNO 2, NO 2. Free ammonia is not released, since it reacts with nitric acid, forming ammonium nitrate:

NH 3 + HNO 3 = NH 4 NO 3

When metals interact with concentrated nitric acid (30–60% HNO 3), the product of HNO 3 reduction is predominantly nitric oxide (IV), regardless of the nature of the metal, for example:

Mg + 4HNO 3 (conc.) = Mg(NO 3) 2 + 2NO 2 + 2H 2 O

Zn + 4HNO 3 (conc.) = Zn(NO 3) 2 + 2NO 2 + 2H 2 O

Hg + 4HNO 3 (conc.) = Hg(NO 3) 2 + 2NO 2 + 2H 2 O

Metals of variable valence, when interacting with concentrated nitric acid, are oxidized to highest degree oxidation. In this case, those metals that are oxidized to an oxidation state of +4 and higher form acids or oxides. For example:

Sn + 4HNO 3 (conc.) = H 2 SnO 3 + 4NO 2 + H 2 O

2Sb + 10HNO 3 (conc.) = Sb 2 O 5 + 10NO 2 + 5H 2 O

Mo + 6HNO 3 (conc.) = H 2 MoO 4 + 6NO 2 + 2H 2 O

Aluminum, chromium, iron, nickel, cobalt, titanium and some other metals are passivated in concentrated nitric acid. After treatment with nitric acid, these metals do not react with other acids.

When metals interact with dilute nitric acid, the product of its reduction depends on the reducing properties of the metal: the more active the metal, the more to a greater extent nitric acid is reduced.

Active metals reduce dilute nitric acid to the maximum, i.e. salt, water and NH 4 NO 3 are formed, for example:

8K + 10HNO 3 (diluted) = 8KNO 3 + NH 4 NO 3 + 3H 2 O

Metals of medium activity, when reacting with dilute nitric acid, form salt, water and nitrogen or N 2 O. The further to the left the metal in this range (the closer to aluminum), the more likely the formation of nitrogen, for example:

5Mn + 12HNO 3 (diluted) = 5Mn(NO 3) 2 + N 2 + 6H 2 O

4Cd + 10HNO 3 (diluted) = 4Cd(NO 3) 2 + N 2 O + 5H 2 O

Low-active metals, when reacting with dilute nitric acid, form salt, water and nitric oxide (II), for example:

3Сu + 8HNO 3 (diluted) = 3Cu(NO 3) 2 + 2NO + 4H 2 O

But the reaction equations in these examples are conditional, since in reality a mixture of nitrogen compounds is obtained, and the higher the activity of the metal and the lower the acid concentration, the lower the degree of oxidation of nitrogen in the product that is formed more than others.

6. Interaction of metals with aqua regia

“Royal vodka” is a mixture of concentrated nitric and hydrochloric acids. It is used to oxidize and dissolve gold, platinum and other precious metals.

Hydrochloric acid in aqua regia is spent on the formation of a complex compound of the oxidized metal. From a comparison of half-reactions 29 and 30 with half-reactions 31–32 (Table 1), it is clear that during the formation of complex compounds of gold and platinum, the redox potential decreases, which makes their oxidation with nitric acid possible. The reaction equations for gold and platinum with aqua regia are written as follows:

Au + HNO 3 + 4HCl = H + NO + 2H 2 O

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

Three metals do not interact with aqua regia: tungsten, niobium and tantalum. They are oxidized with a mixture of concentrated nitric acid and hydrofluoric acid, since hydrofluoric acid forms stronger complex compounds than hydrochloric acid. The reaction equations are as follows:

W + 2HNO3 + 8HF = H2 + 2NO + 4H2O

3Nb + 5HNO3 + 21HF = 3H2 + 5NO + 10H2O

3Ta + 5HNO3 + 24HF = 3H3 + 5NO + 10H2O

In some textbooks There is another explanation for the interaction of noble metals with aqua regia. It is believed that in this mixture between HNO 3 and HCl a reaction catalyzed by noble metals occurs, in which nitric acid oxidizes hydrochloric acid according to the equation:

HNO 3 + 3HCl = NOCl + 2H 2 O

Nitrosyl chloride NOCl is fragile and decomposes according to the equation:

NOCl = NO + Cl(atomic)

Thus, the oxidizing agent of the metal is atomic (i.e., very active) chlorine at the moment of release. Therefore, the products of the interaction of aqua regia with metals are salt (chloride), water and nitric oxide (II):

Au + HNO 3 + 3HCl = AuCl 3 + NO + 2H 2 O

3Pt + 4HNO3 + 12HCl = 3PtCl4 + 4NO + 8H2O,

and complex compounds are formed in the following reactions:

HCl + AuCl 3 = H; 2HCl + PtCl 4 = H 2

The scope of use of nitric acid is very wide. This substance is produced in specialized chemical plants.

The production is very extensive and today you can buy such a solution in very large quantities. Nitric acid is sold in bulk only by certified manufacturers.

Physical characteristics

Nitric acid is a liquid that has a specific pungent odor. Its density is 1.52 g/cm3, and its boiling point is 84 degrees. The process of crystallization of a substance occurs at -41 degrees Celsius, which then turns into a substance white.

Nitric acid is highly soluble in water, and in practice a solution of any concentration can be obtained. The most common is a 70% ratio of the substance. This concentration is the most common and is used everywhere.

A highly saturated acid can release toxic compounds (nitrogen oxides) into the air. They are very harmful and all precautions should be taken when handling it.

A concentrated solution of this substance is a strong oxidizing agent and can react with many organic compounds. So, with prolonged exposure to the skin, it causes burns, which are formed when protein tissues are destroyed.

Nitric acid breaks down easily when exposed to heat and light into nitric oxide, water and oxygen. As already mentioned, the products of such breakdown are very toxic.

She is very aggressive and gets into chemical reactions with most metals, with the exception of gold, platinum and other similar substances. This feature is used to separate gold from other materials such as silver.

When exposed to metals it forms:

nitrates;
hydrated oxides (the formation of one of two types of substances depends on the specific metal).

Nitric acid is a very strong oxidizing agent and therefore this property is used in industrial processes. In most cases, it is used as an aqueous solution of varying concentrations.

Nitric acid plays an important role in the production of nitrogen fertilizers and is also used to dissolve various ores and concentrates. Also included in the process of producing sulfuric acid.

She is an important component"Aqua regia", a substance that can dissolve gold.

We watch the synthesis of nitric acid in the video:

Special properties of nitric and concentrated sulfuric acid.

Nitric acid- HNO3, oxygen-containing monobasic strong acid. Solid nitric acid forms two crystal modifications with monoclinic and orthorhombic lattices. Nitric acid mixes with water in any ratio. In aqueous solutions, it almost completely dissociates into ions. Forms an azeotropic mixture with water with a concentration of 68.4% and boiling point 120 °C at 1 atm. Two solid hydrates are known: monohydrate (HNO3 H2O) and trihydrate (HNO3 3H2O).
Highly concentrated HNO3 is usually brown in color due to the decomposition process that occurs in the light:

HNO3 ---> 4NO2 + O2 + 2H2O

When heated, nitric acid decomposes according to the same reaction. Nitric acid can be distilled (without decomposition) only under reduced pressure.

Nitric acid is strong oxidizing agent , concentrated nitric acid oxidizes sulfur to sulfuric acid, and phosphorus to phosphoric acid; some organic compounds (for example, amines and hydrazine, turpentine) spontaneously ignite upon contact with concentrated nitric acid.

The oxidation degree of nitrogen in nitric acid is 4-5. Acting as an oxidizing agent, HNO can be reduced to various products:

When reacting with dilute nitric acid with low-active metals, for example, with copper, NO is released. In the case of more active metals - iron, zinc - is formed.

Highly dilute nitric acid reacts with active metals-zinc, magnesium, aluminum - with the formation of ammonium ion, which gives ammonium nitrate with acid. Usually several products are formed simultaneously.

Gold, some platinum group metals and tantalum are inert to nitric acid over the entire concentration range, other metals react with it, the course of the reaction being determined by its concentration. Thus, concentrated nitric acid reacts with copper to form nitrogen dioxide, and diluted nitric acid reacts with nitric oxide (II):

Cu + 4HNO3----> Cu(NO3)2 + NO2 + 2H2O

3Cu + 8 HNO3 ----> 3Cu(NO3)2 + 2NO + 4H2O

Most metal c react with nitric acid to release nitrogen oxides in various oxidation states or mixtures thereof; dilute nitric acid, when reacting with active metals, can react to release hydrogen and reduce the nitrate ion to ammonia.

Some metals (iron, chromium, aluminum), which react with dilute nitric acid, are passivated by concentrated nitric acid and are resistant to its effects.

A mixture of nitric and sulfuric acids is called “melange”. Nitric acid is widely used to produce nitro compounds.

A mixture of three volumes of hydrochloric acid and one volume of nitric acid is called “aqua regia.” Aqua regia dissolves most metals, including gold. Its strong oxidizing abilities are due to the resulting atomic chlorine and nitrosyl chloride:

3HCl + HNO3 ----> NOCl + 2 =2H2O

Sulfuric acid– heavy oily liquid that has no color. Miscible with water in any ratio.

Concentrated sulfuric acidactively absorbs water from the air and removes it from other substances. When organic substances enter concentrated sulfuric acid charring occurs, for example, paper:

(C6H10O5)n + H2SO4 => H2SO4 + 5nH2O + 6C

When concentrated sulfuric acid reacts with sugar, a porous carbon mass is formed, similar to a black hardened sponge:

C12H22O11 + H2SO4 => C + H2O + CO2 + Q

Chemical properties dilute and concentrated sulfuric acid are different.

Dilute solutions sulfuric acid react with metals , located in electrochemical series voltages to the left of hydrogen, with the formation of sulfates and the release of hydrogen.

Concentrated solutions sulfuric acid exhibits strong oxidizing properties due to the presence in its molecules of a sulfur atom in the highest oxidation state (+6), therefore concentrated sulfuric acid is a strong oxidizing agent. This is how some nonmetals oxidize:

S + 2H2SO4 => 3SO2 + 2H2O

C + 2H2SO4 => CO2 + 2SO2 + 2H2O

P4 + 8H2SO4 => 4H3PO4 + 7SO2 + S + 2H2O

H2S + H2SO4 => S + SO2 + 2H2O

She interacts with metals , located in the electrochemical voltage series of metals to the right of hydrogen (copper, silver, mercury), with the formation of sulfates, water and sulfur reduction products. Concentrated solutions sulfuric acid don't react with gold and platinum due to their low activity.

a) low-active metals reduce sulfuric acid to sulfur dioxide SO2:

Cu + 2H2SO4 => CuSO4 + SO2 + 2H2O

2Ag + 2H2SO4 => Ag2SO4 + SO2 + 2H2O

b) with metals of intermediate activity, reactions are possible with the release of any of the three products of the reduction of sulfuric acid:

Zn + 2H2SO4 => ZnSO4 + SO2 + 2H2O

3Zn + 4H2SO4 => 3ZnSO4 + S + 4H2O

4Zn + 5H2SO4 => 4ZnSO4 + H2S + 2H2O

c) sulfur or hydrogen sulfide can be released with active metals:

8K + 5H2SO4 => 4K2SO4 + H2S + 4H2O

6Na + 4H2SO4 => 3Na2SO4 + S + 4H2O

d) concentrated sulfuric acid does not interact with aluminum, iron, chromium, cobalt, nickel in the cold (that is, without heating) - passivation of these metals occurs. Therefore, sulfuric acid can be transported in iron containers. However, when heated, both iron and aluminum can interact with it:

2Fe + 6H2SO4 => Fe2(SO4)3 + 3SO2 + 6H2O

2Al + 6H2SO4 => Al2(SO4)3 + 3SO2 + 6H2O

THAT. the depth of sulfur reduction depends on the reducing properties of metals. Active metals (sodium, potassium, lithium) reduce sulfuric acid to hydrogen sulfide, metals located in the voltage range from aluminum to iron - to free sulfur, and metals with less activity - to sulfur dioxide.

Obtaining acids.

1. Oxygen-free acids are obtained by synthesizing hydrogen compounds of non-metals from simple substances and then dissolving the resulting products in water

Non-metal + H 2 = Hydrogen bond of non-metal

H2 + Cl2 = 2HCl

2. Oxoacids are obtained by reacting acid oxides with water.

Acidic oxide + H 2 O = Oxoacid

SO 3 + H 2 O = H 2 SO 4

3. Most acids can be obtained by reacting salts with acids.

Salt + Acid = Salt + Acid

2NaCl + H 2 SO 4 = 2HCl + Na 2 SO 4

Bases are complex substances whose molecules consist of a metal atom and one or more hydroxide groups.

Bases are electrolytes that dissociate to form metal element cations and hydroxide anions.

For example:
KON = K +1 + OH -1

6.Classification of grounds:

1.By the number of hydroxyl groups in the molecule:

a) · Monoacid, the molecules of which contain one hydroxide group.

b) · Diacids, the molecules of which contain two hydroxide groups.

c) · Triacids, the molecules of which contain three hydroxide groups.
2. According to solubility in water: Soluble and Insoluble.

7.Physical properties of bases:

All inorganic bases are solids (except ammonium hydroxide). The grounds have different color: potassium hydroxide - white, copper hydroxide - blue, iron hydroxide - red-brown.

Soluble grounds form solutions that feel soapy to the touch, which is how these substances got their name alkali.

Alkalis form only 10 elements of the periodic table chemical elements D.I. Mendeleev: 6 alkali metals - lithium, sodium, potassium, rubidium, cesium, francium and 4 alkaline earth metals - calcium, strontium, barium, radium.

8. Chemical properties of bases:

1. Aqueous solutions of alkalis change the color of indicators. phenolphthalein - crimson, methyl orange - yellow. This is ensured by the free presence of hydroxo groups in the solution. That is why poorly soluble bases do not give such a reaction.

2. Interact :

a) with acids: Base + Acid = Salt + H 2 O

KOH + HCl = KCl + H2O

b) with acid oxides: Alkali + Acid oxide = Salt + H 2 O

Ca(OH) 2 + CO 2 = CaCO 3 + H 2 O

c) with solutions: Lye solution + Salt solution = New base + New salt

2NaOH + CuSO 4 = Cu(OH) 2 + Na 2 SO 4

d) with amphoteric metals: Zn + 2NaOH = Na 2 ZnO 2 + H 2

Amphoteric hydroxides:

a) React with acids to form salt and water:

Copper(II) hydroxide + 2HBr = CuBr2 + water.

b). React with alkalis: result - salt and water (condition: fusion):

Zn(OH)2 + 2CsOH = salt + 2H2O.

V). React with strong hydroxides: the result is salts if the reaction occurs in an aqueous solution: Cr(OH)3 + 3RbOH = Rb3

When heated, bases that are insoluble in water decompose into the basic oxide and water:

Insoluble Base = Basic Oxide + H2O

Cu(OH) 2 = CuO + H 2 O

Salts – these are products of incomplete replacement of hydrogen atoms in acid molecules with metal atoms or these are products of replacement of hydroxide groups in base molecules with acidic residues .

Salts- these are electrolytes that dissociate to form cations of the metal element and anions of the acid residue.

For example:

K 2 CO 3 = 2K +1 + CO 3 2-

Classification:

Normal salts. These are the products of complete replacement of hydrogen atoms in an acid molecule with non-metal atoms, or the products of complete replacement of hydroxide groups in a base molecule with acidic residues.

Acid salts. These are products of incomplete replacement of hydrogen atoms in the molecules of polybasic acids with metal atoms.

Basic salts. These are products of incomplete replacement of hydroxide groups in molecules of polyacid bases with acidic residues.

Types of salts:

Double salts- they contain two different cations; they are obtained by crystallization from a mixed solution of salts with different cations, but the same anions.

Mixed salts- they contain two different anions.

Hydrate salts(crystalline hydrates) - they contain molecules of water of crystallization.

Complex salts- they contain a complex cation or a complex anion.

A special group consists of salts of organic acids, the properties of which differ significantly from the properties of mineral salts. Some of them can be classified as a special class of organic salts, the so-called ionic liquids or otherwise “liquid salts,” organic salts with a melting point below 100 °C.

Physical properties:

Most salts are white solids. Some salts are colored. For example, potassium orange dichromate, green nickel sulfate.

According to solubility in water salts are divided into soluble in water, slightly soluble in water and insoluble.

Chemical properties:

Soluble salts in aqueous solutions dissociate into ions:

1. Medium salts dissociate into metal cations and anions of acidic residues:

Acid salts dissociate into metal cations and complex anions:

KHSO 3 = K + HSO 3

· Basic metals dissociate into complex cations and anions of acidic residues:

AlOH(CH 3 COO) 2 = AlOH + 2CH 3 COO

2. Salts interact with metals to form a new salt and a new metal: Me(1) + Salt(1) = Me(2) + Salt(2)

CuSO 4 + Fe = FeSO 4 + Cu

3. Solutions interact with alkalis Salt solution + Alkali solution = New salt + New base:

FeCl 3 + 3KOH = Fe(OH) 3 + 3KCl

4. Salts interact with acids Salt + Acid = Salt + Acid:

BaCl 2 + H 2 SO 4 = BaSO 4 + 2HCl

5. Salts can interact with each other Salt(1) + Salt(2) = Salt(3) + Salt(4):

AgNO 3 + KCl = AgCl + KNO 3

6. Basic salts interact with acids Basic salt + Acid = Medium salt + H 2 O:

CuOHCl + HCl = CuCl 2 + H 2 O

7. Acid salts interact with alkalis Acid salt + Alkali = Medium salt + H 2 O:

NaHSO 3 + NaOH = Na 2 SO 3 + H 2 O

8. Many salts decompose when heated: MgCO 3 = MgO + CO 2

Representatives of salts and their meaning:

Salts are widely used both in production and in everyday life:

Salts hydrochloric acid. The most commonly used chlorides are sodium chloride and potassium chloride.

Sodium chloride (table salt) is isolated from lake and sea water, and are also mined in salt mines. Table salt is used for food. In industry, sodium chloride serves as a raw material for the production of chlorine, sodium hydroxide and soda.

Potassium chloride is used in agriculture as potassium fertilizer.

Salts of sulfuric acid. In construction and medicine, semi-aqueous gypsum, obtained by firing rock (calcium sulfate dihydrate), is widely used. When mixed with water, it quickly hardens to form calcium sulfate dihydrate, that is, gypsum.

Sodium sulfate decahydrate is used as a raw material for the production of soda.

Salts of nitric acid. Nitrates are mostly used as fertilizers in agriculture. The most important of them are sodium nitrate, potassium nitrate, calcium nitrate and ammonium nitrate. Usually these salts are called nitrate.

Of the orthophosphates, the most important is calcium orthophosphate. This salt serves as the main component of minerals - phosphorites and apatites. Phosphorites and apatites are used as raw materials in the production of phosphate fertilizers, such as superphosphate and precipitate.

Salts of carbonic acid. Calcium carbonate is used as a raw material to produce lime.

Sodium carbonate (soda) is used in glass production and in soap making.
- Calcium carbonate is also found in nature in the form of limestone, chalk and marble.

The material world in which we live and of which we are a tiny part is one and at the same time infinitely diverse. Unity and diversity chemicals of this world is most clearly manifested in the genetic connection of substances, which is reflected in the so-called genetic series.

Genetic call the connection between substances of different classes based on their mutual transformations.

If the basis of the genetic series in inorganic chemistry is made up of substances formed by one chemical element, then the basis of the genetic series in organic chemistry (chemistry of carbon compounds) is made up of substances with the same number of carbon atoms in the molecule.

Knowledge control:

1. Define salts, bases, acids, their characteristics, main characteristic reactions.

2.Why are acids and bases combined into the group hydroxides? What do they have in common and how are they different? Why does alkali need to be added to a solution of aluminum salt, and not vice versa?

3. Assignment: Give examples of reaction equations illustrating these general properties of insoluble bases.

4. Task: Determine the oxidation state of atoms of metallic elements in the given formulas. What pattern can be observed between their oxidation states in the oxide and the base?

HOMEWORK:

Work through: L2.pp.162-172, retelling of lecture notes No. 5.

Write down the equations of possible reactions according to the diagrams, indicate the types of reactions: a) HCl + CaO ... ;
b) HCl + Al(OH) 3 ...;
c) Mg + HCl ... ;
d) Hg + HCl ... .

Divide substances into classes of compounds. Formulas of substances: H 2 SO 4, NaOH, CuCl 2, Na 2 SO 4, CaO, SO 3, H 3 PO 4, Fe(OH) 3, AgNO 3, Mg(OH) 2, HCl, ZnO, CO 2, Cu 2 O, NO 2

Lecture No. 6.

Topic: Metals. Position of metal elements in the periodic table. Finding metals in nature. Metals. Interaction of metals with non-metals (chlorine, sulfur and oxygen).

Equipment: periodic table of chemical elements, collection of metals, activity series of metals.

Topic study plan

(list of questions required to study):

1. The position of elements - metals in the periodic table, the structure of their atoms.

2. Metals as simple substances. Metal bond, metal crystal lattices.

3. General physical properties metals

4. The prevalence of metal elements and their compounds in nature.

5. Chemical properties of metal elements.

6. The concept of corrosion.

Nitric acid and its properties.

Pure nitric acid HNO 3 is a colorless liquid. In the air, it “smoke”, like concentrated hydrochloric acid, since its vapors form small droplets of fog with the moisture in the air.

Nitric acid is not strong. Already under the influence of light it gradually decomposes:

4HN0 3 = 4N0 2 + 0 2 + 2H 2 0.

The higher the temperature and the more concentrated the acid, the faster the decomposition occurs. The released nitrogen dioxide dissolves in the acid and gives it a brown color.

Nitric acid is one of the strongest acids: in dilute solutions it completely disintegrates into H+ and N0_ ions.

Nitric acid is one of the most energetic oxidizing agents. Many non-metals are easily oxidized by it, turning into the corresponding acids. Thus, sulfur, when boiled with nitric acid, is gradually oxidized into sulfuric acid, phosphorus into phosphoric acid.

Nitric acid acts on almost all metals (see section 11.3.2), turning them into nitrates, and some metals into oxides.

Concentrated HNO 3 passivates some metals.

The oxidation state of nitrogen in nitric acid is +5. Acting as an oxidizing agent, HNO 3 can be reduced to various products:

4 +3 +2 +1 0 -3

N0 2 N 2 0 3 NO N 2 O N 2 NH 4 N0 3

Which of these substances is formed, i.e., how deeply nitric acid is reduced in a given case, depends on the nature of the reducing agent and on the reaction conditions, primarily on the concentration of the acid. The higher the HNO3 concentration, the less deeply it is reduced. When reacting with concentrated acid, NO2 is most often released. When dilute nitric acid reacts with low-active metals, for example, copper, NO is released. In the case of more active metals - iron, zinc - N2O is formed. Highly diluted nitric acid reacts with active metals - zinc, magnesium, aluminum - to form ammonium ion, which gives ammonium nitrate with the acid. Usually several products are formed simultaneously.

Cu + HN0 3(conc.) - Cu(N0 3) 2 + N0 2 + H 2 0;

Cu + HN0 3 (diluted) -^ Cu(N0 3) 2 + N0 + H 2 O;

Mg + HN0 3 (diluted) -> Mg(N0 3) 2 + N 2 0 + n 2 0;

Zn + HN0 3 (very dilute) - Zn(N0 3) 2 + NH 4 N0 3 + H 2 0.

When nitric acid acts on metals, hydrogen, as a rule, is not released.

When non-metals are oxidized, concentrated nitric acid, as in the case of metals, is reduced to NO 2, for example

S + 6HNO 3 = H 2 S0 4 + 6N0 2 + 2H 2 0.

ZR + 5HN0 3 + 2N 2 0 = ZN 3 RO 4 + 5N0

The given diagrams illustrate the most typical cases of interaction of nitric acid with metals and non-metals. In general, redox reactions involving HNO 3 are complex.

A mixture consisting of 1 volume of nitric acid and 3-4 volumes of concentrated hydrochloric acid is called aqua regia. Aqua regia dissolves some metals that do not react with nitric acid, including the “king of metals” - gold. Its action is explained by the fact that nitric acid oxidizes hydrochloric acid with the release of free chlorine and the formation of nitrogen chloroxide (1N), or nitrosyl chloride, N0C1:

HN0 3 + ZNS1 = C1 2 + 2H 2 0 + N0C1.

Nitrosyl chloride is an intermediate product of the reaction and decomposes:

2N0C1 = 2N0 + C1 2.

Chlorine at the moment of release consists of atoms, which determines the high oxidizing ability of aqua regia. The oxidation reactions of gold and platinum proceed mainly according to the following equations:

Au + HN0 3 + ZNS1 = AuCl 3 + NO + 2H 2 0;

3Pt + 4HN0 3 + 12HC1 = 3PtCl 4 + 4N0 + 8H 2 0.

Nitric acid acts on many organic substances in such a way that one or more hydrogen atoms in the molecule of an organic compound are replaced by nitro groups - NO 2. This process is called nitration and has great value in organic chemistry.

Salts of nitric acid are called nitrates. All of them dissolve well in water, and when heated, they decompose, releasing oxygen. In this case, the nitrates of the most active metals turn into nitrites:

2KN0 3 = 2KN0 2 +O 2

Industrial production nitric acid. Modern industrial methods for producing nitric acid are based on the catalytic oxidation of ammonia with atmospheric oxygen. When describing the properties of ammonia, it was indicated that it burns in oxygen, and the reaction products are water and free nitrogen. But in the presence of catalysts, the oxidation of ammonia with oxygen can proceed differently. If a mixture of ammonia and air is passed over the catalyst, then at 750 °C and a certain composition of the mixture, NH 3 is almost completely converted into N0:

4NH 3 (r) + 5O 2 (g) = 4NO (r) + 6H 2 O (g), AN = -907 kJ.

The resulting NO2 easily transforms into NO2, which, with water in the presence of atmospheric oxygen, produces nitric acid.

Platinum-based alloys are used as catalysts for the oxidation of ammonia.

The nitric acid obtained by the oxidation of ammonia has a concentration not exceeding 60%. If necessary, it is concentrated.

The industry produces diluted nitric acid with concentrations of 55, 47 and 45%, and concentrated nitric acid - 98 and 97%. Concentrated acid is transported in aluminum tanks, diluted acid is transported in tanks made of acid-resistant steel.

Ticket 5

2. The role of iron in the life processes of the body.

Iron in the body. Iron is present in the bodies of all animals and in plants (on average about 0.02%); it is necessary mainly for oxygen metabolism and oxidative processes. There are organisms (so-called concentrators) capable of accumulating it in large quantities (for example, iron bacteria - up to 17-20% of iron). Almost all of the iron in animals and plants is bound to proteins. Iron deficiency causes growth retardation and chlorosis in plants associated with reduced chlorophyll formation. Excess Iron also has a harmful effect on plant development, causing, for example, sterility of rice flowers and chlorosis. In alkaline soils, Iron compounds are formed that are inaccessible for absorption by plant roots, and plants do not receive it in sufficient quantities; in acidic soils, iron turns into soluble compounds in excess quantities. When there is a deficiency or excess of assimilable iron compounds in the soil, plant diseases can be observed over large areas.

Iron enters the body of animals and humans with food (the richest sources in it are liver, meat, eggs, legumes, bread, cereals, spinach, and beets). Normally, a person receives 60-110 mg of Iron in their diet, which significantly exceeds it daily requirement. Absorption of iron received from food occurs in the upper part of the small intestines, from where it enters the blood in protein-bound form and is carried with the blood to various organs and tissues, where it is deposited in the form of an iron-protein complex - ferritin. The main depot of iron in the body is the liver and spleen. Due to ferritin, the synthesis of all iron-containing compounds of the body occurs: the respiratory pigment hemoglobin is synthesized in the bone marrow, myoglobin is synthesized in muscles, cytochromes and other iron-containing enzymes are synthesized in various tissues. Iron is released from the body mainly through the wall of the large intestines (in humans, about 6-10 mg per day) and to a small extent by the kidneys.

: monohydrate (HNO 3 ·H 2 O) and trihydrate (HNO 3 ·3H 2 O).

Physical and physico-chemical properties

Phase diagram of an aqueous solution of nitric acid.

Nitrogen in nitric acid is tetravalent, oxidation state +5. Nitric acid is a colorless liquid that fumes in air, melting point −41.59 °C, boiling point +82.6 °C with partial decomposition. The solubility of nitric acid in water is not limited. Aqueous solutions of HNO 3 with a mass fraction of 0.95-0.98 are called “fuming nitric acid”, with a mass fraction of 0.6-0.7 - concentrated nitric acid. Forms an azeotropic mixture with water (mass fraction 68.4%, d 20 = 1.41 g/cm, T bp = 120.7 °C)

When crystallized from aqueous solutions, nitric acid forms crystalline hydrates:

monohydrate HNO 3 H 2 O, T pl = −37.62 °C
trihydrate HNO 3 3H 2 O, T pl = −18.47 °C

Solid nitric acid forms two crystalline modifications:

monoclinic, space group P 2 1/a, a= 1.623 nm, b= 0.857 nm, c= 0.631, β = 90°, Z = 16;

The monohydrate forms crystals in the orthorhombic system, space group P na2, a= 0.631 nm, b= 0.869 nm, c= 0.544, Z = 4;

The density of aqueous solutions of nitric acid as a function of its concentration is described by the equation

where d is the density in g/cm³, c is the mass fraction of acid. This formula poorly describes the behavior of density at concentrations greater than 97%.

Chemical properties

Highly concentrated HNO 3 is usually brown in color due to the decomposition process that occurs in the light:

When heated, nitric acid decomposes according to the same reaction. Nitric acid can be distilled (without decomposition) only under reduced pressure (the indicated boiling point at atmospheric pressure is found by extrapolation).

c) displaces weak acids from their salts:

When boiling or exposed to light, nitric acid partially decomposes:

Nitric acid at any concentration exhibits the properties of an oxidizing acid, with nitrogen being reduced to an oxidation state from +4 to −3. The depth of reduction depends primarily on the nature of the reducing agent and the concentration of nitric acid. As an oxidizing acid, HNO 3 interacts:

Nitrates

Nitric acid is a strong acid. Its salts - nitrates - are obtained by the action of HNO 3 on metals, oxides, hydroxides or carbonates. All nitrates are highly soluble in water. Nitrate ion does not hydrolyze in water.

Salts of nitric acid decompose irreversibly when heated, and the composition of the decomposition products is determined by the cation:

a) nitrates of metals located in the voltage series to the left of magnesium:

b) nitrates of metals located in the voltage range between magnesium and copper:

c) nitrates of metals located in the voltage series to the right:

Nitrates in aqueous solutions exhibit practically no oxidizing properties, but at high temperatures in the solid state they are strong oxidizing agents, for example, when fusing solids:

Historical information

The method of obtaining dilute nitric acid by dry distillation of saltpeter with alum and copper sulfate was apparently first described in the treatises of Jabir (Geber in Latinized translations) in the 8th century. This method, with various modifications, the most significant of which was the replacement of copper sulfate with iron sulfate, was used in European and Arab alchemy until the 17th century.

In the 17th century, Glauber proposed a method for producing volatile acids by reacting their salts with concentrated sulfuric acid, including nitric acid from potassium nitrate, which made it possible to introduce concentrated nitric acid into chemical practice and study its properties. Method