8 julio, 2024

Potassium fluoride (KF): what it is, structure, properties, uses

What is potassium fluoride?He potassium fluoride It is an inorganic halide that consists of a salt formed between the metal and the halogen. Its chemical formula is KF, which means that for every K+ cation there is an F– counterpart. The interactions are electrostatic, and as a consequence there are no KF covalent bonds.

This salt is characterized by its extreme solubility in water, which is why it forms hydrates, absorbs moisture and is deliquescent. Therefore, it is very easy to prepare aqueous solutions of it, which serve as a source of fluoride anions for all those syntheses where it is desired to incorporate it into some structure.

KI is produced by reacting potassium carbonate with hydrofluoric acid, producing potassium bifluoride (KHF2), which, by thermal decomposition, ends up producing potassium fluoride.

Potassium Fluoride Structure

The top image shows the structure of potassium fluoride. The purple spheres represent K+ cations, while the yellowish spheres represent F– anions.

Note that the arrangement is cubic and corresponds to a rock salt type structure, very similar to that of sodium chloride. All spheres are surrounded by six neighbors, which make up a KF6 or FK6 octahedron, that is, each K+ is surrounded by six F–, and the same occurs vice versa.

It was previously mentioned that KF is hygroscopic and therefore absorbs moisture from the environment. Thus, the arrangement shown would correspond to the anhydrous form (without water) and not to its hydrates, which absorb so much water that they even become solubilized and «melt» (deliquescence).

hydrates

The crystal structures of the hydrates become less simple. Because now the water molecules are directly involved in the arrangements and interact with the K+ and F– ions. Some of the most stable hydrates are KF·2H2O and KF·4H2O.

In both hydrates the octahedrons just mentioned are deformed by the water molecules. This is mainly due to hydrogen bonding between F– and H₂O (F–—HOH). Crystallographic studies have determined that, despite this, the two ions continue to maintain the same number of neighbors.

As a result, the original cubic structure for anhydrous potassium fluoride is transformed into a monoclinic and even rhombohedral arrangement.

The anhydrous share the deliquescent property, so its white crystals, if left in contact with a cold mist, would turn watery in a short time.

Potassium Fluoride Properties

Molecular weight: 58.097 g/mol.
Physical appearance (color):cwhite cubic crystals or deliquescent white crystalline powder.
Flavor:sacute saline odor.
Boiling point: 2741°F at 760mmHg (1502°C). In the liquid state it becomes electrically conductive, although F– anions may do not collaborate to the same degree in conduction as the K+.
Melting point: 1576°F; 858°C; 1131K (anhydrous KF). This is indicative of its strong ionic bonds.
Solubility:ssoluble in HF, but insoluble in alcohol. This shows that hydrogen bonds between fluoride and alcohols, F–—HOR, do not favor the solvation process over the dissolution of its crystalline network.
Water solubility: tonhydro 92 g/100 ml (18 °C); 102g/100ml (25°C); dihydrate 349.3 g/100 ml (18 °C). That is, as the KF hydrates, it becomes more soluble in water.
Density: 2.48g/cm3.
Vapor pressure: 100 kPa (750 mmHg) at 1499°C.
Decomposition: cWhen heated to decomposition, it emits a toxic fume of potassium oxide and hydrogen fluoride.
corrosive action: orAn aqueous solution corrodes glass and porcelain.
Flashpoint: noor is it a flammable substance
Experimental refractive index (ηD): 1,363.
Stability: andstable if protected from moisture, otherwise the solid will dissolve. Incompatible with strong acids and bases.

Potassium Fluoride Uses

adjust pH: himAqueous potassium fluoride solutions are used in industrial applications and processes. For example, KF solutions allow adjustment of the pH in manufacturing that takes place in textile processing facilities and in laundries (approximate it to a value of 7).
fluoride source:ePotassium fluoride is, after hydrogen fluoride, the main source of obtaining fluorine. This element is used in nuclear plants and in the production of inorganic and organic compounds, some with uses such as its incorporation into toothpastes.
Fluorocarbon synthesis:ePotassium fluoride can be used in the synthesis of fluorcarbon or fluorcarbon from chlorocarbon, using the Finkeistein reaction. In this reaction, ethylene glycol and dimethyl sulfoxide are used as solvents.
fluorination:cSince it is a source of fluoride where it lies dissolved in water, complex fluorides can be synthesized from its solutions, that is, an F– is incorporated into them. to the structures. An example is found in the following chemical equation:

MnBr2(ac) + 3KF(ac) => KMnF3(s) + 2KBr(ac)

The mixed fluoride of KMnF3 then precipitates. Thus, F– could be added to form part of a complex metal salt. In addition to manganese, fluorides of other metals can be precipitated: KCoF3, KFeF3, KNiF3, KCuF3 and KZnF3.
Likewise, fluorine can be covalently incorporated into an aromatic ring, synthesizing organofluorines.
Several:el KF is used as an intermediate or raw material for the synthesis of compounds that are mainly used in agrochemicals or pesticide products.
In addition, it is used as a solder flux agent and in glass engraving, that is, its aqueous solution eats away at the glass surface and, on a mould, prints the desired finish.

References

Potassium fluoride. Retrieved from chemicalbook.com.
Potassium fluoride. Retrieved from pubchem.ncbi.nlm.nih.gov.

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