The 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 each cation K+ there is an F- counterpart. As can be seen, the interactions are electrostatic, and as a consequence there are no covalent K-F 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..
Above is cation K+ (purple sphere) and the anion F- (bluish sphere). Both ions interact attracting each other by their +1 and -1 charges.
Although KF is not as dangerous as HF, the fact that it has the anion F-, makes it a toxic salt. That is why their solutions have been used as insecticides.
KI is produced by reacting potassium carbonate with hydrofluoric acid, producing potassium bifluoride (KHFtwo); which by thermal decomposition ends up originating potassium fluoride.
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The upper image shows the structure of potassium fluoride. The purple spheres, as in the first image, represent the K cations+; while the yellowish spheres represent the anions F-.
Note that the arrangement is cubic and corresponds to a rock-salt-like structure, very similar to that of sodium chloride. All the spheres are surrounded by six neighbors, which make up an octahedron KF6 or FK6; that is, each K+ surrounds himself with six F-, and the same happens in vice versa.
It was mentioned earlier that KF is hygroscopic and therefore absorbs moisture from the environment. This being the case, 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).
The crystal structures of hydrates become less simple. Why? Because now the water molecules intervene directly in the arrangements and interact with the K ions+ and F-. One of the most stable hydrates is KF2HtwoO and KF 4HtwoOR.
In both hydrates the octahedra just mentioned are deformed by the water molecules. This is mainly due to the hydrogen bonds between the F- and the HtwoO (F--HOH). Crystallographic studies have determined that despite this the two ions continue to have the same number of neighbors.
As a result of all this, the original cubic structure for anhydrous potassium fluoride becomes a monoclinic and even rhombohedral arrangement..
Anhydrous ones share the deliquescent property, so their white crystals, if left in contact with a cold mist, would become watery in a short time..
58.097 g / mol.
White cubic crystals or deliquescent white crystalline powder.
Sharp salty taste.
2,741 ° F to 760 mmHg (1502 ° C). In the liquid state it becomes a conductor of electricity, although the anions F- do not collaborate to the same degree as the K+.
1,576 ° F; 858 ° C; 1131 K (anhydrous KF). This is indicative of its strong ionic bonds..
Soluble in HF, but insoluble in alcohol. This shows that hydrogen bonds between fluoride and alcohols, F--HOR, do not favor the solvation process against the dissolution of its crystalline lattice.
Anhydrous 92 g / 100 ml (18 ° C); 102 g / 100 ml (25 ° C); dihydrate 349.3 g / 100 ml (18 ° C). That is, as KF is hydrated, it becomes more soluble in water..
2.48 g / cm3.
100 kPa (750 mmHg) at 1,499 ºC.
When heated to decomposition it emits toxic smoke of potassium oxide and hydrogen fluoride..
A watery solution corrodes glass and porcelain.
It is not a flammable substance
1,363.
Stable if protected from moisture, otherwise the solid will dissolve. Incompatible with strong acids and bases.
Aqueous potassium fluoride solutions are used in industrial applications and processes; For example, KF solutions allow the pH to be adjusted in manufacturing in textile processing facilities and in laundries (they approximate it to a value of 7).
Potassium 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 in toothpastes..
Potassium fluoride can be used in the synthesis of fluorocarbon or fluorocarbon from chlorocarbon, using the Finkeistein reaction. Ethylene glycol and dimethyl sulfoxide are used as solvents in this reaction..
As it is a source of fluorine where it lies dissolved in water, complex fluorides can be synthesized from its solutions; that is, an F is added to them- to structures. An example is in the following chemical equation:
MnBrtwo(ac) + 3KF (ac) => KMnF3(s) + 2KBr (ac)
KMnF mixed fluoride then precipitates3. Thus, F- so that it is 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 organofluorides.
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 fluxing agent for welding and glass etching; that is, its aqueous solution eats away at the surface of the glass and, on a mold, prints the desired finish.
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