Manganese acid is an inorganic unstable compound with the formula HMnO 4 . It can not be confused with any other substance, because it is characterized by a bright, saturated violet-red color.
This is a strong electrolyte in which molecules (electrically neutral particles) are almost completely dissociated into ions. Despite the fact that it exists only in solutions, because as a separate substance is not obtained. However, all its features can be described in more detail.
Chemical properties
In liquids, manganese acid gradually decomposes. This process is accompanied by the release of oxygen (chalcogen, chemically active non-metal).
As a result, a precipitate of manganese dioxide is formed. Here is how this process with the participation of manganese acid looks in the formula: 4HMnO 4 → 4MnO 2 ↓ + 3O 2 ↑ + 2H 2 O.
The resulting compound is MnO 2 . A dark brown powder that does not dissolve in water. It is the most stable compound of manganese, which belongs to the group of ferrous metals.
Also, the subject compound exhibits features common to strong acids. In particular, it enters into neutralization reactions - interacts with alkalis, forming salts and water. As a rule, such processes are exometrical, that is, accompanied by the release of heat. Here is one example: HMnO 4 + NaOH → NaMnO 4 + H 2 O.
It is also worth mentioning that manganese acid, like its permanganates (salts), is a powerful oxidizing agent, an electron acceptor. Here is an example demonstrating this: 2HMnO 4 + 14HCl → 2MnCl 2 + 5Cl 2 ↑ + 8H 2 O.
Physical properties
As mentioned earlier, manganese acid, the graphic formula of which is shown above, has not been deduced in its pure form. The maximum concentration in aqueous solutions having a characteristic bright lilac color does not exceed 20%.
This substance is susceptible to temperature readings. If it is less than 20 ° C, then the solution forms a crystalline hydrate - a solid that occurs due to the bonding of cations (positively charged ions) and water molecules. Its formula is as follows: HMnO 4 ⋅ 2H 2 O. Ionic structure: (H 5 O 2 ) + (MnO 4 ) - .
Also, speaking about the physical properties of manganese acid, it is worth noting its molar mass. It is 119.94 g / mol.
Acid production
Most often, this substance is obtained by conducting a reaction between two compounds - diluted sulfuric acid and a solution of barium permanganate, an element with high chemical activity. The result is an insoluble precipitate of its sulfate. But it is removed through filtering. It looks like this: Ba (MnO 4 ) + H 2 SO 4 → 2HMnO 4 + BaSO 4 ↓.
There is another way to obtain this acid. It is based on the cold interaction of water and manganese oxide. This, by the way, is an oily liquid, which comes in two shades (brown-green or scarlet). Whatever the color, there will always be a metallic sheen. He is stable at room temperature. And when combined with flammable substances, it ignites them, often with an explosion. So, the reaction formula looks like this: Mn 2 O 7 + H 2 O → 2HMnO 4 .
Dioxide Characterization
This substance, which has already been mentioned above, is found in large quantities in the earth's crust. In the form of a mineral called pyrolusite. Usually black or steel gray. Its crystals are small, have a columnar or needle-like appearance. The following properties are characteristic of a mineral:
- Piezoelectric . Manifest in the occurrence of polarization of the dielectric - the displacement of bound charges in it or by the rotation of electric dipoles.
- Semiconductor . Manifest in an increase in electrical conductivity with increasing temperature.
It is also worth noting that the dioxide is soluble in hydrochloric acid, which is accompanied by the release of chlorine.
The use of pyrolusite
Electrolytic manganese acid dioxide is widely used in the production of batteries and galvanic cells - chemical sources of electric current, which are usually based on the interaction of two metals or their oxides in an electrolyte. It is also used for:
- The formation of catalysts - chemicals that accelerate the reaction, but are not included in its composition. A striking example is hopcalite. They are filled with additional gas masks to protect against carbon monoxide.
- The formation of substances such as manganese salt and potassium permanganate - crystals of dark purple, almost black in color, which, dissolving in water, lead to the formation of a bright crimson liquid. The formula is KMnO 4 .
- Discoloration of green glasses.
- Manufacture of oil and varnish in the paint industry.
- For the manufacture of chrome leather in the leather sphere.
It is interesting that scientists determined that pieces of pyrolusite from the Pesh de Laze cave located in southern France consist of pure manganese dioxide. It is believed that Neanderthals, who lived 350-600 thousand years ago, used it as a catalyst and oxidizer of combustion and oxidation reactions.
Permanganate (potassium permanganate)
This substance is familiar to many. However, about its application - a little later. It is more important to note that it is precisely with the help of permanganate that many ODS of manganese acid (redox reactions) occur.
This is due to its exceptional chemical properties. Depending on the hydrogen index (pH) of the solution formed by permanganate, it is possible to oxidize various substances, with reduction to compounds of many degrees of oxidation.
There are many examples. In an acidic environment, reduction to manganese (II) compounds will occur, in a neutral indicator it will be equal to (IV), and in a highly alkaline one it will be equal to (VI). Here's what it looks like:
- In an acidic environment: 2KMnO 4 + 5K 2 SO 3 + 3H 2 SO 4 → 6K 2 SO 4 + 2MnSO 4 + 3H 2 O.
- B neutral: 2KMnO 4 + 3K 2 SO 3 + 2 → 3K 2 SO 4 + 2MnO 2 + 2KOH.
- B alkaline: 2KMnO 4 + K 2 SO 3 + 2KOH → K 2 SO 4 + 2K 2 MnO 4 + H 2 O. This reaction in this form occurs with a lack of reducing agent and in the presence of highly concentrated alkali. Such conditions provide a delay in hydrolysis.
It is worth noting that, in contact with concentrated sulfuric acid, the substance explodes. Ho, if permanganate is carefully combined with this cold substance, then unstable manganese oxide is formed.
Use of potassium permanganate
The permanganate of the substance in question has a powerful antiseptic effect. Particularly widely used in medicine are diluted solutions with a concentration of 0.1%, which I use to treat burns, gargle and wash wounds. It is also an effective emetic for poisoning with alkonides such as aconitine and morphine. Only in such cases use a less concentrated solution diluted to 0.02-0.1%.
The pharmacological effect is not typical. When the solution comes in contact with organic substances, atomic oxygen is released. The oxide in its composition forms compounds such as albuminates with proteins. In small concentrations, they have an astringent effect, and in large concentrations they are irritating, tanning and cauterizing. Therefore, the final effect depends on how the permanganate of manganese acid will be diluted - strongly or weakly.
Other applications
Potassium permanganate is actually a substance actively used in various fields. In addition to medicine, it is involved:
- When washing laboratory glassware. Perfectly removes fats and organic matter.
- In pyrotechnics as an oxidizing agent.
- When determining permanganate oxidizability in the process of assessing water quality according to GOST 2761-84 (Kubel method).
- When tinting photographs.
- For pickling wood. The liquid is used as a stain (a substance that gives color).
- For risky removal of a tattoo. The liquid burns out the skin, and the tissue with paint dies. It hurts, and scars still remain.
- As an oxidizing agent in the formation of para- and metaphthalic acids.
Finally, I would like to make a reservation that potassium permanganate is on the fourth list of precursors of the Russian Standing Committee on Drug Control.