Potassium Nitrate: Formula, Structure, Uses, How It's Done and Properties

He potassium nitrate It is a ternary salt composed of potassium, alkali metal, and oxoanion nitrate. Its chemical formula is KNO 3 , which means that for every K ion + , there is an NO ion 3 ÂÂ- interacting with this. Therefore, it is an ionic salt and constitutes one of the alkali nitrates (LiNO 3 , NaNO 3 , RbNO 3 ...)

The KNO 3 It is a strong oxidizing agent due to the presence of the nitrate anion. That is to say, it acts as a reserve of ions, solid nitrates and anhydrides, unlike other salts highly soluble in water or very hygroscopic. Many of the properties and uses of this compound are due to the nitrate anion, rather than the potassium cation.

In the image above, KNO crystals are illustrated 3 with needle shapes. The natural source of KNO 3 is the saltpeter, known by the names Saltpeter or salpetre , in English. This element is also known as potassium nitrate or nitro mineral.

It is found in arid or desert areas, as well as efflorescence of the cavernous walls. Another important source of KNO 3 is the guano, excrement of animals that inhabit dry environments.

Index

  • 1 Chemical structure
    • 1.1 Other crystalline phases
  • 2 Applications
  • 3 How is it done?
  • 4 Physical and chemical properties
  • 5 References

Chemical structure

The crystal structure of the KNO is represented in the upper image 3 . The purple spheres correspond to the K ions + , while the red and blue are the oxygen and nitrogen atoms, respectively. The crystal structure is orthorhombic at room temperature.

The geometry of the NO anion 3 - is that of a trigonal plane, with the oxygen atoms at the vertices of the triangle, and the nitrogen atom at its center. It has a positive formal charge on the nitrogen atom, and two negative formal charges on two oxygen atoms (1-2 = (-1)).

These two negative charges of NO 3 - they are delocalised among the three oxygen atoms, always maintaining the positive charge on the nitrogen. As a consequence of the above, the K ions + of the crystal avoid placing just above or below the nitrogen of the anions NO 3 - .

In fact, the image shows how the K ions + they are surrounded by oxygen atoms, red spheres. In conclusion, these interactions are responsible for the crystal arrangements.

Other crystalline phases

Variables such as pressure and temperature can modify these arrangements and originate different structural phases for the KNO 3 (phases I, II and III). For example, phase II is that of the image, while phase I (with trigonal crystalline structure) is formed when the crystals are heated to 129 ° C.

Phase III is a transitional solid obtained from the cooling of phase I, and some studies have shown that it exhibits some important physical properties, such as ferroelectricity. In this phase the crystal forms layers of potassium and nitrates, possibly sensitive to electrostatic repulsions between the ions.

In the layers of phase III the anions do NOT 3 - they lose a little of their planarity (the triangle curves slightly) to allow this arrangement, which, before any mechanical disturbance, becomes the structure of phase II.

Applications

Salt is of great importance since it is used in many activities of man, which are manifested in industry, agriculture, food, etc. Among these uses, the following stand out:

- The preservation of food, especially meat. Despite the suspicion that it is involved in the formation of nitrosamine (carcinogenic agent) it is still used in charcuterie.

- Fertilizer, because potassium nitrate provides two of the three macronutrients of plants: nitrogen and potassium. Together with phosphorus, this element is necessary for the development of plants. That is, it is an important and manageable reserve of these nutrients.

- It accelerates the combustion, being able to produce explosions if the combustible material is extensive or if it is finely divided (greater surface area, greater reactivity). In addition, it is one of the main components of gunpowder.

- It facilitates the removal of the stumps of the felled trees. The nitrate supplies the necessary nitrogen for the fungi to destroy the wood of the stumps.

- It intervenes in the reduction of tooth sensitivity through its incorporation in dentifrices, which increases the protection to the painful sensations of the tooth produced by cold, heat, acid, sweet or contact.

- It acts as a hypotensor in the regulation of blood pressure in humans. This effect would be given or interrelated with a change in sodium excretion. The recommended dose in the treatment is 40-80 mEq / day of potassium. In this regard, it is pointed out that potassium nitrate would have a diuretic action.

How is it done?

Most of the nitrate is produced in the mines of the deserts in Chile. It can be synthesized by several reactions:

NH 4 DO NOT 3 (ac) + KOH (ac) => NH 3 (ac) + KNO 3 (ac) + H 2 O (l)

Potassium nitrate is also produced by neutralizing nitric acid with potassium hydroxide in a highly exothermic reaction.

KOH (ac) + HNO 3 (conc) => KNO 3 (ac) + H 2 O (l)

On an industrial scale, potassium nitrate is produced by a double displacement reaction.

Elder brother 3 (ac) + KCl (ac) => NaCl (ac) + KNO 3 (ac)

The main source of KCl is silvin mineral, and not other minerals such as carnallite or cainite, which are also composed of ionic magnesium.

Physical and chemical properties

Potassium nitrate in the solid state is presented as a white powder or in the form of crystals of orthohombic structure at room temperature, and trigonal at 129 ° C. It has a molecular weight of 101.1032 g / mol, is odorless and has an acrid saline taste.

It is a compound very soluble in water (316-320 g / liter of water, at 20 ºC), due to its ionic nature and the ease of water molecules to solvate ion K + .

Its density is 2.1 g / cm 3 at 25 ° C. This means that it is approximately twice as dense as water.

Its melting point (334 ° C) and boiling point (400 ° C) are indicative of the ionic bonds between K + and not 3 - . However, they are low compared to other salts, because the crystal lattice energy is lower for monovalent ions (ie, with charges ± 1), and also have sizes that are not very similar.

It decomposes at a temperature close to the boiling point (400 ºC) to produce potassium nitrite and molecular oxygen:

KNO 3 (s) => KNO 2 (s) + O 2 (g)

References

  1. Pubchem. (2018). Potassium Nitrate. Retrieved on April 12, 2018, from: pubchem.ncbi.nlm.nik.gov
  2. Anne Marie Helmenstine, Ph.D. (September 29, 2017). Saltpeter or Potassium Nitrate Facts. Retrieved on April 12, 2018, from: thoughtco.com
  3. K. Nimmo & B. W. Lucas. (May 22, 1972). Conformation and Orientation of NO3 in α-Phase Potassium Nitrate. Nature Physical Science 237, 61-63.
  4. Adam Rędzikowski. (April 8, 2017). Potassium nitrate crystals. [Figure]. Retrieved on April 12, 2018, from: https://commons.wikimedia.org
  5. Acta Cryst. (2009). Growth and single-crystal refinement of phase-III potassium nitrate, KNO 3 . B65, 659-663.
  6. Marni Wolfe. (October 3, 2017). Potassium Nitrate Risks. Retrieved on April 12, 2018, from: livestrong.com
  7. Amethyst Galleries, Inc. (1995-2014). The mineral niter. Retrieved on April 12, 2018, from: galleries.com


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