Very dilute nitric acid. Nitrous and nitric acids and their salts

DEFINITION

Pure Nitric acid- a colorless liquid, at -42 o C solidifying into a transparent crystalline mass (the structure of the molecule is shown in Fig. 1).

In air, it, like concentrated hydrochloric acid, "smokes", since its vapors form small droplets of fog with air moisture.

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

4HNO 3 \u003d 4NO 2 + O 2 + 2H 2 O.

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

Rice. 1. The structure of the molecule nitric acid.

Table 1. Physical properties nitric acid.

Obtaining nitric acid

Nitric acid is formed as a result of the action of oxidizing agents on nitrous acid:

5HNO 2 + 2KMnO 4 + 3H 2 SO 4 = 5HNO 3 + 2MnSO 4 + K 2 SO 4 + 3H 2 O.

Anhydrous nitric acid can be obtained by distillation under reduced pressure of a concentrated solution of nitric acid in the presence of P 4 O 10 or H 2 SO 4 in all glass equipment without lubrication in the dark.

The industrial process for the production of nitric acid is based on the catalytic oxidation of ammonia over heated platinum:

NH 3 + 2O 2 \u003d HNO 3 + H 2 O.

Chemical properties of nitric acid

Nitric acid is one of the strongest acids; in dilute solutions, it completely dissociates into ions. Its salts are called nitrates.

HNO 3 ↔H + + NO 3 -.

characteristic property nitric acid is its pronounced oxidizing ability. Nitric acid is one of the most energetic oxidizers. Many non-metals are easily oxidized by it, turning into the corresponding acids. So, when sulfur is boiled with nitric acid, it gradually oxidizes to sulfuric acid, phosphorus - in phosphoric. A smoldering ember immersed in concentrated HNO 3 flares up brightly.

Nitric acid acts on almost all metals (with the exception of gold, platinum, tantalum, rhodium, iridium), turning them into nitrates, and some metals into oxides.

Concentrated nitric acid passivates some metals.

When dilute nitric acid reacts with inactive metals, such as copper, nitrogen dioxide is released. In the case of more active metals - iron, zinc - dinitrogen oxide is formed. Highly dilute nitric acid reacts with active metals - zinc, magnesium, aluminum - to form an ammonium ion, which gives ammonium nitrate with acid. Usually several products are formed simultaneously.

Cu + HNO 3 (conc) = Cu(NO 3) 2 + NO 2 + H 2 O;

Cu + HNO 3 (dilute) = Cu(NO 3) 2 + NO + H 2 O;

Mg + HNO 3 (dilute) = Mg (NO 3) 2 + N 2 O + H 2 O;

Zn + HNO 3 (highly dilute) = Zn(NO 3) 2 + NH 4 NO 3 + H 2 O.

Under the action of nitric acid on metals, hydrogen, as a rule, is not released.

S + 6HNO 3 \u003d H 2 SO 4 + 6NO 2 + 2H 2 O;

3P + 5HNO 3 + 2H 2 O \u003d 3H 3 PO 4 + 5NO.

A mixture consisting of 1 volume of nitrogen and 3-4 volumes of concentrated of hydrochloric acid, is called aqua regia. Royal vodka dissolves some metals that do not interact 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 (III) chloride, or nitrosyl chloride, NOCl:

HNO 3 + 3HCl \u003d Cl 2 + 2H 2 O + NOCl.

The use of nitric acid

Nitric acid is one of the most important compounds of nitrogen: in large quantities it is used in the production of nitrogen fertilizers, explosives and organic dyes, serves as an oxidizing agent in many chemical processes, used in the production of sulfuric acid by the nitrous method, used for the manufacture of cellulose varnishes, film.

Examples of problem solving

EXAMPLE 1

The scope of use of nitric acid is very wide. Such a substance is made at 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 the boiling point is 84 degrees. The process of crystallization of the substance occurs at -41 degrees Celsius, which then turns into a white substance.

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

A highly saturated acid is capable of releasing toxic compounds (nitrogen oxides) into the air. They are very harmful and all precautions should be observed 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 during the destruction of protein tissues.

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

It is very corrosive and reacts chemically with most metals except for gold, platinum and other similar substances. This feature used to separate gold from other materials such as silver.

When exposed to metals, it forms:

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

Nitric acid is a very strong oxidizing agent and therefore given property used in industrial processes. In most cases, it is used as water solution different concentration.

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

She happens to be important component"royal vodka", a substance that can dissolve gold.

Synthesis of nitric acid, see the video:

Nitric acid - important but dangerous chemical reagent

Chemical reagents, laboratory equipment and instruments, as well as glass laboratory glassware or from other materials are components of any modern industrial or research laboratory. In this list, as well as many centuries ago, special place occupied by substances and compounds, since they represent the main chemical base, without which it is impossible to carry out any, even the simplest experiment or analysis.

Modern chemistry has a huge number of chemical reagents: alkalis, acids, reagents, salts and others. Among them, acids are the most common group. Acids are complex hydrogen-containing compounds whose atoms can be replaced by metal atoms. The scope of their application is extensive. It covers many branches of production: chemical, machine-building, oil refining, food, as well as medicine, pharmacology, cosmetology; widely used in everyday life.

Nitric acid and its definition

refers to monobasic acids and is a strong reagent. It is a transparent liquid, which may have a yellowish tint when stored for a long time in a warm room, since nitrogen oxides accumulate in it at positive (room) temperature. When heated or interacting with direct sunbeams acquires a brown color due to the process of release of nitrogen dioxide. Smokes on contact with air. This acid is a strong oxidizing agent with a sharp bad smell, which reacts with most metals (with the exception of platinum, rhodium, gold, tantalum, iridium and some others), turning them into oxides or nitrates. This acid is highly soluble in water, and in any ratio, limitedly in ether.

The release form of nitric acid depends on its concentration:

- regular - 65%, 68%;
- smoky - 86% and more. The color of the "smoke" can be white if the concentration is from 86% to 95%, or red - over 95%.

Receipt

Currently, the production of highly or weakly concentrated nitric acid goes through the following stages:
1. process of catalytic oxidation of synthetic ammonia;
2. as a result - obtaining a mixture of nitrous gases;
3. water absorption;
4. the process of concentrating nitric acid.

Storage and transportation

This reagent is the most aggressive acid, Therefore, the following requirements are put forward for its transportation and storage:
- store and transport in special hermetically sealed tanks made of chromium steel or aluminum, as well as in bottles made of laboratory glass.

Each container is marked with the inscription "Dangerous".

Where is the chemical used?

The scope of nitric acid is currently huge. It covers many industries such as:
- chemical (production of explosives, organic dyes, plastics, sodium, potassium, plastics, some types of acids, artificial fibers);
- agricultural (production of nitrogen mineral fertilizers or saltpeter);
- metallurgical (dissolution and pickling of metals);
- pharmacological (included in preparations for the removal of skin formations);
- jewelry production (determination of the purity of precious metals and alloys);
- military (included in explosives as a nitrating agent);
- rocket and space (one of the components rocket fuel);
- medicine (for cauterization of warts and other skin formations).

Precautionary measures

When working with nitric acid, it must be taken into account that this chemical reagent is a strong acid, which belongs to substances of the 3rd hazard class. For laboratory staff, as well as persons admitted to work with such substances, there are special rules. To avoid direct contact with the reagent, all work must be carried out strictly in special clothing, which includes: acid-proof gloves and shoes, overalls, nitrile gloves, as well as glasses and respirators, as means of protecting the respiratory and vision organs. Failure to comply with these requirements can lead to the most serious consequences: in case of contact with the skin - burns, ulcers, and if inhaled - poisoning, up to pulmonary edema.

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

NH 3 + HNO 3 \u003d NH 4 NO 3

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

Mg + 4HNO 3 (conc.) \u003d 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.) \u003d Hg (NO 3) 2 + 2NO 2 + 2H 2 O

Metals variable valence when interacting with concentrated nitric acid, they are oxidized to the highest degree oxidation. In this case, those metals that are oxidized to an oxidation state of +4 and above 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 interact with other acids.

In the interaction of metals with dilute nitric acid, the product of its reduction depends on reducing properties metal: the more active the metal, the more nitric acid is reduced.

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

8K + 10HNO 3 (razb.) \u003d 8KNO 3 + NH 4 NO 3 + 3H 2 O

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

5Mn + 12HNO 3 (diff.) \u003d 5Mn (NO 3) 2 + N 2 + 6H 2 O

4Cd + 10HNO 3 (diff.) \u003d 4Cd (NO 3) 2 + N 2 O + 5H 2 O

Inactive metals, when interacting with dilute nitric acid, form salt, water and nitric oxide (II), for example:

3Cu + 8HNO 3 (razb.) \u003d 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 metal activity and the lower the acid concentration, the lower the degree of nitrogen oxidation in the product, which is formed more than others.

6. Interaction of metals with "royal vodka"

"Aqua regia" 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. A comparison of half-reactions 29 and 30 with half-reactions 31–32 (Table 1) shows that the redox potential decreases during the formation of complex compounds of gold and platinum, which makes their oxidation with nitric acid possible. The equations for the reactions of gold and platinum with "aqua regia" are written as follows:

Au + HNO 3 + 4HCl \u003d H + NO + 2H 2 O

3Pt + 4HNO 3 + 18HCl = 3H 2 + 4NO + 8H 2 O

Three metals do not interact with "royal vodka": 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 + 2HNO 3 + 8HF = H 2 + 2NO + 4H 2 O

3Nb + 5HNO 3 + 21HF = 3H 2 + 5NO + 10H 2 O

3Ta + 5HNO 3 + 24HF = 3H 3 + 5NO + 10H 2 O

In some teaching aids there is another explanation for the interaction of noble metals with "royal vodka". 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 \u003d NOCl + 2H 2 O

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

NOCl = NO + Cl(atomic)

Thus, the metal oxidizing agent is atomic (i.e., very active) chlorine at the time 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 + 4HNO 3 + 12HCl = 3PtCl 4 + 4NO + 8H 2 O,

and complex compounds are formed in the following reactions:

HCl + AuCl 3 = H; 2HCl + PtCl 4 \u003d H 2

Nitric acid(HNO 3) - one of the strong monobasic acids with a pungent suffocating odor, sensitive to light and in bright light decomposes into one of the nitrogen oxides (also called brown gas - NO 2) and water. Therefore, it is desirable to store it in dark containers. In a concentrated state, it does not dissolve aluminum and iron, so it can be stored in appropriate metal containers.

Nitric acid is strong electrolyte like many acids) and a very strong oxidizing agent. It is often used in reactions with organic substances.

Anhydrous nitric acid- a colorless volatile liquid (bp = 83 ° C; due to volatility, anhydrous nitric acid is called "fuming") with a pungent odor.

Nitric acid, like ozone, can be formed in the atmosphere during lightning flashes. Nitrogen, which makes up 78% of the composition atmospheric air, reacts with atmospheric oxygen, forming nitric oxide NO. Upon further oxidation in air, this oxide turns into nitrogen dioxide (brown gas NO2), which reacts with atmospheric moisture (clouds and fog), forming nitric acid. But such a small amount is completely harmless to the ecology of the earth and living organisms.

One volume of nitric acid and three volumes of hydrochloric acid form a compound called "royal vodka". It is able to dissolve metals (platinum and gold) that are insoluble in ordinary acids. When paper, straw, cotton are introduced into this mixture, vigorous oxidation will occur, even ignition.

When boiled, it decomposes into its constituent components (chemical decomposition reaction):

HNO 3 \u003d 2NO 2 + O 2 + 2H 2 O - brown gas (NO 2), oxygen and water are released.

Nitric acid
(when heated, a brown gas is released)

Properties of nitric acid

Properties of nitric acid can be diverse even in reactions with the same substance. They are directly related to the concentration nitric acid. Consider options for chemical reactions.

- nitric acid concentrated:

With metals iron (Fe), chromium (Cr), aluminum (Al), gold (Au), platinum (Pt), iridium (Ir), sodium (Na) - does not interact due to the formation of a protective film on their surface, which does not allows further oxidation of the metal.

With everyone else metals during a chemical reaction, brown gas (NO 2) is released. For example, in a chemical reaction with copper (Cu):
4HNO 3 conc. + Cu \u003d Cu (NO 3) 2 + 2NO 2 + H 2 O
With non-metals, such as phosphorus:
5HNO 3 conc. + P \u003d H 3 PO 4 + 5NO 2 + H 2 O

- decomposition of nitric acid salts

Depending on the dissolved metal, the decomposition of salt at temperature occurs as follows:
Any metal (marked as Me) up to magnesium (Mg):
MeNO 3 \u003d MeNO 2 + O 2
Any metal from magnesium (Mg) to copper (Cu):
MeNO 3 \u003d MeO + NO 2 + O 2
Any metal after copper (Cu):
MeNO 3 \u003d Me + NO 2 + O 2

- nitric acid diluted:

When interacting with alkaline earth metals, as well as zinc (Zn), iron (Fe), it is oxidized to ammonia (NH 3) or to ammonium nitrate (NH 4 NO 3). For example, when reacting with magnesium (Mg):
10HNO 3 diluted + 4Zn = 4Zn(NO 3) 2 + NH 4 NO 3 + 3H 2 O
But nitrous oxide (N 2 O) can also be formed, for example, when reacting with magnesium (Mg):
10HNO 3 diluted + 4Mg \u003d 4Mg (NO 3) 2 + N 2 O + 5H 2 O
Reacts with other metals to form nitric oxide (NO), for example, dissolves silver (Ag):
2HNO 3 diluted + Ag \u003d AgNO 3 + NO + H 2 O
Reacts similarly with non-metals, such as sulfur:
2HNO 3 diluted + S \u003d H 2 SO 4 + 2NO - oxidation of sulfur to the formation of sulfuric acid and the release of nitrogen oxide gas.

Chemical reaction with metal oxides, e.g. calcium oxide:

2HNO 3 + CaO = Ca(NO 3) 2 + H 2 O - salt (calcium nitrate) and water are formed

Chemical reaction with hydroxides (or bases), such as slaked lime

2HNO 3 + Ca(OH) 2 = Ca(NO 3) 2 + H 2 O - salt (calcium nitrate) and water are formed - neutralization reaction

Chemical reaction with salts, such as chalk:

2HNO 3 + CaCO 3 \u003d Ca (NO 3) 2 + H 2 O + CO 2 - a salt (calcium nitrate) and another acid are formed (in this case carbonic acid is formed, which decomposes into water and carbon dioxide).