One of the very first mineral acids that has become known to man is sulfuric, or sulfate. Not only she herself, but many of her salts were used in construction, medicine, food industry, and for technical purposes. So far, nothing has changed in this regard. A number of characteristics that sulfate acid possesses make it simply indispensable in chemical synthesis. In addition, in almost all branches of life and industry, its salt is used. Therefore, we will consider in detail what it is and what are the features of the manifested properties.
Variety of names
To begin with, there are many names for this substance. Among them, there are those that are formed according to rational nomenclature, and those that have historically developed. So, this compound is designated as:
- sulfate acid;
- oil of vitriol;
- sulfuric acid;
- oleum.
Although the term "oleum" is not quite suitable for this substance, since it is a mixture of sulfuric acid and higher sulfur oxide - SO 3 .
Sulfate acid: the formula and structure of the molecule
From the point of view of chemical abbreviations, the formula of this acid can be written as follows: H 2 SO 4 . Obviously, the molecule consists of two hydrogen cations and an anion of the acid residue - the sulfate ion, which has a charge of 2+.
In this case, the following bonds act inside the molecule:
- covalent polar between sulfur and oxygen;
- covalent strongly polar between hydrogen and the acid residue SO 4 .
Sulfur, having 6 unpaired electrons, forms two double bonds with two oxygen atoms. Even with a pair - single, and those, in turn, are single with hydrogens. As a result, the structure of the molecule allows it to be strong enough. At the same time, the hydrogen cation is very mobile and easily leaves, because sulfur and oxygen are much more electronegative. By pulling the electron density onto themselves, they provide hydrogen with a partially positive charge, which becomes complete when disconnected. Thus, acidic solutions are formed in which H + is present.
If we talk about the oxidation states of elements in the compound, then sulfate acid, the formula of which is H 2 SO 4 , can easily calculate them: for hydrogen +1, for oxygen -2, for sulfur +6.
As in any molecule, the total charge is zero.
Discovery story
Sulfate acid has been known to people since antiquity. Even alchemists knew how to get it by calcining various vitriol. From the very ninth century, people received and used this substance. Later in Europe, Albert Magnus learned to extract acid during the decomposition of iron sulfate.
However, none of the methods was profitable. Then the so-called chamber synthesis option became known. To do this, sulfur and nitrate were burned, and the released vapors were absorbed by water. As a result, sulfate acid was formed.
Even later, the British managed to find the cheapest method of obtaining this substance. For this, pyrite - FeS 2 , iron pyrite was used. Its roasting and subsequent interaction with oxygen are still one of the most important industrial methods for the synthesis of sulfuric acid. Such raw materials are more affordable, cheap and of high quality for large volumes of production.
Physical properties
There are several parameters, including external ones, according to which sulfate acid differs from others. Its physical properties can be described in several paragraphs:
- Under standard conditions - liquid.
- In a concentrated state it is heavy, oily, for which it received the name "vitriol oil".
- The density of the substance is 1.84 g / cm 3 .
- It is colorless and odorless.
- It has a pronounced "copper" taste.
- It dissolves in water very well, almost unlimited.
- Hygroscopic, able to trap both free and bound water from tissues.
- Non-volatile.
- Boiling point - 296 about C.
- Melting at 10.3 about C.
One of the most important features of this compound is its ability to hydrate with the release of a large amount of heat. That is why, even from school, children are encouraged that water should not be added to acid in any case, but only vice versa. Indeed, in terms of density, water is easier, therefore, it will accumulate on the surface. If you add it sharply to acid, then as a result of the dissolution reaction, so much energy will be released that the water will boil and begin to spray with particles of a dangerous substance. This can cause severe chemical burns to the skin of the hands.
Therefore, it is necessary to pour acid into water in a thin stream, then the mixture will heat up very much, but boiling will not occur, which means that the liquid will also spray.
Chemical properties
From the point of view of chemistry, this acid is very strong, especially if it is a concentrated solution. It is dibasic, therefore, it dissociates stepwise, with the formation of the hydrosulfate and sulfate anions.
In general, its interaction with various compounds corresponds to all the main reactions characteristic of this class of substances. Examples of several equations in which sulfate acid is involved can be given. Chemical properties are manifested in its interaction with:
- salts;
- metal oxides and hydroxides;
- amphoteric oxides and hydroxides;
- metals in a series of stresses up to hydrogen.
As a result of such interactions, in almost all cases, middle salts of a given acid (sulfates) or acidic (hydrosulfates) are formed.
A special feature is also the fact that only a solution of this substance, that is, a dilute acid, reacts with metals according to the usual Me + H 2 SO 4 = MeSO 4 + H 2 ↑ scheme. If we take concentrated or highly saturated (oleum), then the interaction products will be completely different.
Special properties of sulfuric acid
These include precisely the interaction of concentrated solutions with metals. So, there is a certain scheme that reflects the whole principle of such reactions:
- If the metal is active, the result is the formation of hydrogen sulfide, salt and water. That is, sulfur is reduced to -2.
- If the metal is of medium activity, then the result is sulfur, salt and water. That is, the reduction of the sulfate ion to free sulfur.
- Metals of low chemical activity (after hydrogen) are sulfur dioxide, salt and water. Sulfur in the oxidation state +4.
Also special properties of sulfate acid are the ability to oxidize some non-metals to their highest oxidation state and to react with complex compounds and oxidize them to simple substances.
Production Methods in Industry
The sulfate process for producing sulfuric acid consists of two main types:
Both are the most common ways in industry in all countries of the world. The first option is based on the use of iron pyrite or sulfur pyrite - FeS 2 as a raw material. There are three stages in total:
- Raw material firing with the formation of sulfur dioxide gas as a combustion product.
- The transmission of this gas through oxygen over a vanadium catalyst with the formation of sulfuric anhydride - SO 3 .
- In the absorption tower, anhydride is dissolved in a solution of sulfate acid with the formation of a solution of high concentration - oleum. Very heavy oily thick liquid.
The second option is almost the same, but nitrogen oxides are used as a catalyst. From the point of view of parameters such as product quality, cost and energy consumption, raw material purity, productivity, the first method is more efficient and acceptable, therefore it is most often used.
Laboratory Synthesis
If it is necessary to obtain sulfuric acid in small quantities for laboratory research, the best way is the interaction of hydrogen sulfide with sulfates of inactive metals.
In these cases, the formation of ferrous metal sulfides occurs, and sulfuric acid is formed as a by-product. For small studies, this option is suitable, however, such acid will not differ in purity.
Also in the laboratory, you can conduct a high-quality reaction to sulfate solutions. The most common reagent is barium chloride, since the Ba 2+ ion, together with the sulfate anion, precipitates into a white precipitate - barite milk: H 2 SO 4 + BaCL 2 = 2HCL + BaSO 4 ↓
The most common salts
The sulfate acid and sulfates that it forms are important compounds in many industries and households, including food. The most common salts of sulfuric acid are the following:
- Gypsum (alabaster, selenite). The chemical name is aqueous calcium sulfate crystalline hydrate. Formula: CaSO 4 . It is used in construction, medicine, the pulp and paper industry, and the manufacture of jewelry.
- Barite (heavy spar). Barium sulfate. The solution is a milky precipitate. In solid form - transparent crystals. Used in optical instruments, x-rays, for the manufacture of an insulating coating.
- Mirabilite (Glauber's salt). The chemical name is sodium hydrogen sulfate decahydrate. Formula: Na 2 SO 4 * 10H 2 O. It is used in medicine as a laxative.
One can cite as examples many salts that are of practical importance. However, the above are the most common.
Sulphate liquor
This substance is a solution that is formed due to the heat treatment of wood, that is, cellulose. The main purpose of this compound is to obtain sulfate soap on its basis by the settling method. The chemical composition of sulfate liquor is as follows:
- lignin;
- hydroxy acids;
- monosaccharides;
- phenols;
- resins;
- volatile and fatty acids;
- sulfides, chlorides, carbonates and sodium sulfates.
There are two main types of this substance: white and black sulfate liquor. White goes to pulp and paper production, and black is used to produce sulfate soap in industry.
Main applications
The annual production of sulfuric acid is 160 million tons per year. This is a very significant figure, which indicates the importance and prevalence of this compound. There are several industries and places where the use of sulfate acid is necessary:
- In batteries as an electrolyte, especially in lead.
- In factories where sulfate fertilizers are produced. The bulk of this acid goes precisely to the manufacture of mineral fertilizers for plants. Therefore, plants for the production of sulfuric acid and the manufacture of fertilizers are most often built nearby.
- In the food industry as an emulsifier, indicated by code E513.
- In numerous organic syntheses as a dewatering agent, a catalyst. This gives explosives, resins, cleaning and washing products, caprons, polypropylene and ethylene, dyes, chemical fibers, esters and other compounds.
- Used in filters for water purification and the manufacture of distilled water.
- Used in the extraction and processing of rare elements from ore.
Also, a lot of sulfuric acid goes to laboratory tests, where it is obtained by local methods.