The potassium nitrite is an inorganic salt whose chemical formula is KNOtwo, which is chemically and pharmacologically related to potassium nitrate, KNO3. Its physical appearance consists of yellowish white crystals, highly hygroscopic, and therefore deliquescent; that is, they dissolve quickly in humid environments.
Its formula indicates that the proportion of K ions+ and notwo- is 1: 1, and they are held together by electrostatic forces or ionic bonds. No pure natural sources appear to have been found for its crystals, although nitrite anions can be found in soils, fertilizers, plants and animals..
The image above shows what the KNO crystals look liketwo, with pronounced yellow tones. If these crystals are left in contact with the air, they will absorb moisture until they become an aqueous solution; solution that has generated controversies regarding whether or not its use for medical purposes is beneficial.
On the other hand, its crystals, in very small quantities (200 ppm), are used to salinize meats and guarantee their preservation against bacterial action. Likewise, the KNOtwo improves the color of meats, making them more reddish; however, it is subject to several restrictions to avoid the toxic effects of this salt in the body.
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The ions present in potassium nitrite are shown above. The K cation+ corresponds to the purple sphere, while the anion NOtwo- is represented by the bluish and red spheres.
Anion NOtwo- shown with one double and one single bond [O = N-O]-; but in reality, both bonds are equal product of the resonance of the negative charge between them.
K ions+ and notwo- they attract each other in space until they organize a structural pattern with the least energy; this is, where the repulsions between equal charges are minimal. And so they create KNO crystalstwo, whose unit cell is susceptible to temperature changes, which phase transitions.
For example, at low temperatures (less than 25 ° C) KNO crystalstwo adopt a monoclinic system (phase I). When the temperature exceeds 25 ° C, a phase transition from monoclinic to rhombohedral (phase II) occurs. Finally, above 40 ° C the KNO crystalstwo change to be cubic (phase III).
Likewise, the KNOtwo it can exhibit other crystalline phases (phases IV, V and VI) under high pressures. With this, the K ions+ and notwo- they end up moving and ordering in different ways in their pure crystals.
85.1038 g / mol.
1.9150 g / mL.
440.02 ° C (but begins to decompose from 350 ° C, emitting toxic fumes).
537 ° C (explodes).
312 g / 100 g water at 25 ° C.
Its solubility in water is such that it is hygroscopic; so much so that it exhibits deliquescence, absorbing enough moisture to dissolve. This affinity for water may be due to the energy stability gained by K ions.+ when hydrated, as well as a low lattice enthalpy for KNO crystalstwo.
Crystals can absorb water without dissolving to become a hydrate, KNOtwoHtwoO. In the hydrate the water molecule is found accompanying the ions, which modifies the crystalline structure.
This hydrate (or several of them), can be formed below -9 ° C; at higher temperatures, the water dissolves and hydrates the ions, deforming the crystal.
Slightly soluble in hot alcohols, and very soluble in ammonia.
6-9. Its aqueous solutions are therefore alkaline, since the anion NOtwo- can be hydrolyzed.
To the KNOtwo it can also be named in other ways. 'Potassium nitrite' corresponds to the name for this salt according to the stock nomenclature; 'potassium nitrite', according to the systematic nomenclature, in which the only valence of potassium is highlighted, +1; and potassium dioxonitrate (III), according to the systematic nomenclature.
The name 'potassium dioxonitrate (III)' highlights the +3 valence of the nitrogen atom. Although it is the most recommended name by the IUPAC for the KNOtwo, 'potassium nitrite' continues to be the most convenient and the easiest to remember.
The most direct way to synthesize it, but with a lower yield, is through the thermal decomposition of potassium nitrate or saltpeter at 400 ° C or more:
2KNO3 => KNOtwo + ORtwo
However, part of the KNOtwo ends up decomposing by heat, in addition to other products are formed.
Another method to prepare or synthesize it with a higher yield is by reducing the KNO3 in the presence of lead, copper or zinc. The equation for this reaction is as follows:
KNO3 + Pb => KNOtwo + PbO
Potassium nitrate and lead are mixed stoichiometrically in an iron skillet, where they melt with constant stirring and heating for half an hour. Lead (II) oxide is yellow in color, and the resulting mass is pulverized hot and treated with boiling water. Then the hot mixture is filtered.
The hot filtrate is bubbled with carbon dioxide for five minutes, which will precipitate lead carbonate, PbCO3, insoluble. In this way, the lead is separated from the filtrate. Dilute nitric acid is added to the filtrate until the pH is neutral, it is allowed to cool, and finally the water is evaporated so that the KNO crystals are formed.two.
Potassium nitrite is used as an additive to cure red meat, maintaining its flavor and color for a longer time during storage, while delaying the action of bacteria and certain toxins, such as botulinum. Therefore, it exhibits antibacterial action.
The KNOtwo it oxidizes to NO, which reacts with myoglobin in the meat and, consequently, ends up changing its natural red color. Later, when the meat is cooked it acquires its characteristic strong pink color.
However, under conditions without specifying the KNOtwo reacts with meat proteins to give rise to nitrosamines, which can become carcinogenic.
On the other hand, the KNOtwo (although preferably NaNOtwo) is an analytical reagent that can be used in the synthesis of azo dyes (the reaction of nitrous acid with aromatic amines), and in the analysis of amino acids.
While it has its negative effects, the KNOtwo acts as an antidote in patients poisoned with cyanides and hydrogen sulfide. Its mechanism consists of oxidizing the Fe centerstwo+ to Faith3+ of the groups we have hemoglobins, producing methemoglobin, which then reacts with the CN anions- and HS-.
In the gastric juice of the stomach the anion NOtwo- it is reduced to NO, which is known to have a vasodilator action, increasing blood flow. In other regions of the body where the pH is not acidic enough, some enzymes, such as xanthine oxidoreductase, are responsible for reducing NOtwo-.
KNO has been usedtwo to treat ailments and diseases such as angina pectoris and epilepsy (with very negative side effects).
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