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, substances and compounds occupy a special place, 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 exposed to direct sunlight, it turns brown due to the process of releasing nitrogen dioxide. Smokes on contact with air. This acid is a strong oxidizing agent with a pungent odor that 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:

- ordinary - 65%, 68%;
- smoky - 86% or more. The color of the "smoke" may be white if the concentration is between 86% and 95%, or red above 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 of 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. There are special rules for laboratory employees, as well as persons authorized to work with such substances. 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.

Modern chemistry is a science that operates with a large number of reagents. These can be salts, reagents, alkalis. But the most numerous group is acids. These are complex compounds based on hydrogen. In this case, foreign atoms here can be replaced by metal atoms. Acids are used in various branches of human activity. For example, in medicine, the food industry, in the production of household goods. That is why this group of reagents should be especially carefully studied.

Basic information about nitric acid

This is a strong reagent that belongs to the category of monocomponent acids. It looks like a normal clear liquid. Sometimes there is a yellowish tinge. This is due to the fact that at a warm temperature, nitric oxide accumulates on the surface. Nitrogen dioxide may also appear as a brown precipitate. But it happens under the sun. When exposed to air, the acid begins to smoke strongly. In addition, it normally reacts with metals. It dissolves perfectly in water, but in the case of ether there are a number of limitations.

What forms of release exist? In total, two are shared - ordinary (concentration 65-68%) and smoky (at least 85%). In this case, the color of the smoke can vary greatly. If the concentration is 86-95%, then it is white. Is the percentage higher? Then you will see red.

Receipt process

Today it does not differ both in the case of strong and weak concentration. It can be divided into several stages.

Crystalline oxidation of synthetic ammonia occurs.
It is necessary to wait until nitrous gases form.
All the water contained in the composition is absorbed.
At the final stage, it is necessary to wait until the acid reaches the required concentration.

How is storage and transportation?

This reagent does not belong to the category of particularly aggressive. Therefore, there are not so many requirements for storage and transportation. It is required to keep the acid in sealed containers made of aluminum or chromium steel. Laboratory glass is also suitable. As for the tanks, they should be marked "Dangerous". The same applies to small containers.

Precautions for use

This chemical reagent belongs to strong acids. It has III hazard class. Those persons who are allowed to work with this substance must receive appropriate instruction. In the room you must be in special clothing. It includes overalls, gloves, respirators, goggles. Individual respiratory and eye protection equipment is required. The consequences of non-compliance with safety requirements can be serious. If the acid gets on the skin, it will cause burns and ulcers. Will you breathe it in? Then you will get very poisoned or even get pulmonary edema. So in the laboratories it is necessary to organize constant monitoring, ask employees to be instructed on safety measures.

Where is nitric acid used?

Due to its chemical properties, this acid is used in many industries. A few should be singled out. First of all, it is industry. With it, you can easily synthesize artificial fibers. In addition, often nitric acid is the main component in the manufacture of motor oil. Surely you know that it is used in metallurgy. With it, you can dissolve and etch metals. There is a special industrial nitric acid that does a better job of solving the problems described.

Application in everyday life

It is used to make products that allow you to effectively clean jewelry at home. But you need to be extremely careful not to allow these products to come into contact with the skin. With drip irrigation, nitric acid can be used as a cleaner. A concentration of 60% will be enough to get rid of salts or dissolve sediment in a drip system.

What is the application in medicine?

If you look at the composition of some medicines, you will see that they contain nitric acid. For example, 30% is used to fight warts. Also often this component is added to the means to combat peptic ulcers. It is an excellent antiseptic with astringent properties.

Agricultural use

Agronomists need mineral fertilizers in order to make the crop richer. Some of them contain nitric acid. But it is necessary to clearly calculate the dose so that the resulting vegetables and fruits do not cause any harm to health. If there is too much acid, then nitrates will accumulate in the cultures. There are several types of acid-based fertilizers: amide, ammonia, nitrate.

But this reagent has salts, which are used even more often in agriculture. They are added to some drugs that are given to animals.

What can be said in conclusion?

As you can see, nitric acid is a very important component that is used in a huge number of industries. Without it, it would be impossible to imagine modern life. And chemists on a regular basis come up with where else this reagent can be used.

In contact with

Nitric acid HNO 3 is a colorless liquid, has a pungent odor, and evaporates easily. If it comes into contact with the skin, nitric acid can cause severe burns (a characteristic yellow spot forms on the skin, it should immediately be washed with plenty of water and then neutralized with NaHCO 3 soda)

Nitric acid

Molecular formula: HNO 3 , B(N) = IV, C.O. (N) = +5

The nitrogen atom forms 3 bonds with oxygen atoms by the exchange mechanism and 1 bond by the donor-acceptor mechanism.

Physical Properties

Anhydrous HNO 3 at ordinary temperature is a colorless volatile liquid with a specific odor (bp 82.6 "C).

Concentrated "fuming" HNO 3 has a red or yellow color, as it decomposes with the release of NO 2 . Nitric acid is miscible with water in any ratio.

How to get

I. Industrial - 3-stage synthesis according to the scheme: NH 3 → NO → NO 2 → HNO 3

Stage 1: 4NH 3 + 5O 2 = 4NO + 6H 2 O

Stage 2: 2NO + O 2 = 2NO 2

Stage 3: 4NO 2 + O 2 + 2H 2 O = 4HNO 3

II. Laboratory - prolonged heating of saltpeter with conc. H2SO4:

2NaNO 3 (solid) + H 2 SO 4 (conc.) = 2HNO 3 + Na 2 SO 4

Ba (NO 3) 2 (tv) + H 2 SO 4 (conc.) = 2HNO 3 + BaSO 4

Chemical properties

HNO 3 as a strong acid exhibits all the general properties of acids

HNO 3 → H + + NO 3 -

HNO 3 is a very reactive substance. In chemical reactions, it manifests itself as a strong acid and as a strong oxidizing agent.

HNO 3 interacts:

a) with metal oxides 2HNO 3 + CuO = Cu(NO 3) 2 + H 2 O

b) with bases and amphoteric hydroxides 2HNO 3 + Cu(OH) 2 = Cu(NO 3) 2 + 2H 2 O

c) with salts of weak acids 2HNO 3 + CaCO 3 = Ca(NO 3) 2 + CO 2 + H 2 O

d) with ammonia HNO 3 + NH 3 = NH 4 NO 3

The difference between HNO 3 and other acids

1. When HNO 3 interacts with metals, H 2 is almost never released, since H + ions of the acid do not participate in the oxidation of metals.

2. Instead of H + ions, NO 3 - anions have an oxidizing effect.

3. HNO 3 is capable of dissolving not only metals located in the activity row to the left of hydrogen, but also low-active metals - Cu, Ag, Hg. In a mixture with HCl, it also dissolves Au, Pt.

HNO 3 is a very strong oxidizing agent

I. Oxidation of metals:

Interaction of HNO 3: a) with low and medium activity Me: 4HNO 3 (conc.) + Сu = 2NO 2 + Cu(NO 3) 2 + 2H 2 O

8HNO 3 (razb.) + 3Сu \u003d 2NO + 3Cu (NO 3) 2 + 4H 2 O

b) with active Me: 10HNO 3 (razb.) + 4Zn \u003d N 2 O + 4Zn (NO 3) 2 + 5H 2 O

c) with alkaline and alkaline earth Me: 10HNO 3 (very dilute) + 4Са = NH 4 NO 3 + 4Ca (NO 3) 2 + 3H 2 O

Very concentrated HNO 3 at normal temperature does not dissolve some metals, including Fe, Al, Cr.

II. Oxidation of non-metals:

HNO 3 oxidizes P, S, C to their higher S.O., while itself is reduced to NO (HNO 3 dilute) or to NO 2 (HNO 3 conc).

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

2HNO 3 + S = 2NO + H 2 SO 4

III. Oxidation of complex substances:

Particularly important are the oxidation reactions of certain Me sulfides, which are insoluble in other acids. Examples:

8HNO 3 + PbS \u003d 8NO 2 + PbSO 4 + 4H 2 O

22HNO 3 + 3Сu 2 S \u003d 10NO + 6Cu (NO 3) 2 + 3H 2 SO 4 + 8H 2 O

HNO 3 - nitrating agent in organic synthesis reactions

R-H + HO-NO 2 → R-NO 2 + H 2 O

C 2 H 6 + HNO 3 → C 2 H 5 NO 2 + H 2 O nitroethane

C 6 H 5 CH 3 + 3HNO 3 → C 6 H 2 (NO 2) 3 CH 3 + ZH 2 O trinitrotoluene

C 6 H 5 OH + 3HNO 3 → C 6 H 5 (NO 2) 3 OH + ZH 2 O trinitrophenol

HNO 3 esterifies alcohols

R-OH + HO-NO 2 → R-O-NO 2 + H 2 O

C 3 H 5 (OH) 3 + 3HNO 3 → C 3 H 5 (ONO 2) 3 + ZH 2 O glycerol trinitrate

Decomposition of HNO 3

When stored in the light, and especially when heated, HNO 3 molecules decompose due to intramolecular redox:

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

A red-brown poisonous gas NO 2 is released, which enhances the aggressive oxidizing properties of HNO 3

Salts of nitric acid - nitrates Me (NO 3) n

Nitrates are colorless crystalline substances, soluble in water. They have chemical properties characteristic of typical salts.

Distinctive features:

1) redox decomposition when heated;

2) strong oxidizing properties of molten alkali metal nitrates.

Thermal decomposition

1. Decomposition of nitrates of alkali and alkaline earth metals:

Me(NO 3) n → Me(NO 2) n + O 2

2. Decomposition of metal nitrates in the activity series of metals from Mg to Cu:

Me(NO 3) n → Me x O y + NO 2 + O 2

3. Decomposition of metal nitrates in the activity series of metals above Cu:

Me(NO 3) n → Me + NO 2 + O 2

Examples of typical reactions:

1) 2NaNO 3 \u003d 2NaNO 2 + O 2

2) 2Cu(NO 3) 2 = 2CuO + 4NO 2 + O 2

3) 2AgNO 3 \u003d 2Ag + 2NO 2 + O 2

Oxidative action of melts of alkali metal nitrates

In aqueous solutions, nitrates, in contrast to HNO 3 , show almost no oxidative activity. However, melts of alkali metal and ammonium nitrates (nitrate) are strong oxidizing agents, since they decompose with the release of active oxygen.

Chemical properties of nitric acid

Nitric acid is characterized by properties: common with other acids and specific:

CHEMICAL PROPERTIES IN COMMON WITH OTHER ACIDS

1. Very strong acid. Indicators in its solution change color to red.

Dissociates in aqueous solution almost completely:

HNO 3 → H + + NO 3 -

2. Reacts with basic oxides

K 2 O + 2HNO 3 → 2KNO 3 + H 2 O

K 2 O + 2H + + 2NO 3 - → 2K + + 2NO 3 - + H 2 O

K 2 O + 2 H + → 2 K + + H 2 O

3. Reacts with bases

HNO 3 + NaOH → NaNO 3 + H 2 O

H + + NO 3 - + Na + + OH - → Na + + NO 3 - + H 2 O

H + + OH - → H 2 O

4. Reacts with salts, displaces weak acids from their salts

2HNO 3 + Na 2 CO 3 → 2NaNO 3 + H 2 O + CO 2

2H + + 2NO 3 - + 2Na + + C O 3 2- → 2Na + + 2NO 3 - + H 2 O + CO 2

2 H + + C O 3 2- → H 2 O + CO 2

SPECIFIC PROPERTIES OF NITRIC ACID

Nitric acid is a strong oxidizing agent

N +5 → N +4 → N +2 → N +1 → No → N -3

N +5 + 8 e - → N -3 oxidizing agent is reduced.

1. Decomposes in the light and when heated

4HNO 3 t˚C → 2H 2 O + 4NO 2 + O 2

Brown gas is formed

2. Colors squirrels orange-yellow (in case of contact with the skin of the hands - "xantoprotein reaction")

3. Reacts with metals.

Depending on the concentration of the acid and the position of the metal in N. Beketov's electrochemical series of voltages, various nitrogen-containing products can be formed.

When interacting with metals, hydrogen is never released

HNO 3 + Me= salt +H 2 O+ X

: 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 fuming 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 \u003d -37.62 ° C
• trihydrate HNO 3 3H 2 O, T pl \u003d -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;

Monohydrate forms orthorhombic crystals, 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 the acid. This formula poorly describes the behavior of density at a concentration of more than 97%.

Chemical properties

Highly concentrated HNO 3 usually has a brown color due to the decomposition process taking place in the light:

When heated, nitric acid decomposes according to the same reaction. Nitric acid can only be distilled (without decomposition) 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 in any concentration exhibits the properties of an oxidizing acid, while nitrogen is reduced to an oxidation state of +4 to -3. The depth of reduction depends primarily on the nature of the reducing agent and on 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. The 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 standing in the series of voltages to the left of magnesium:

b) nitrates of metals located in a series of voltages between magnesium and copper:

c) nitrates of metals located in a row of voltages to the right:

Nitrates in aqueous solutions practically do not show oxidizing properties, but at high temperatures in the solid state they are strong oxidizing agents, for example, when solids are fused:

Historical information

The technique for 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 Arabic alchemy until the 17th century.

In the 17th century, Glauber proposed a method for obtaining volatile acids by the reaction of 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