POTASSIUM HYPOCHLORITE (KOCL): STRUCTURE, PROPERTIES - CHEMISTRY - 2024

The potassium hypochlorite is the potassium salt of hypochlorous acid. It is also a ternary salt of potassium, oxygen and chlorine, and constitutes an inorganic compound. Its chemical formula is KOCl, which means that the K ⁺ cation and the OCl ^- anion are found in the ionic solid in a 1: 1 stoichiometric ratio.

Of its homologous compounds (LiOCl, NaOCl, Ca (OCl) ₂) it is perhaps the least used and popularly known within the chemical and pragmatic culture. All these salts have the common denominator of the hypochlorite anion (OCl ^-), which gives them their main characteristics as a bleaching agent.

Hypochlorous acid

The history of potassium hypochlorite and its physicochemical properties are similar to the sodium hypochlorite salt. It was initially produced in 1789 by Claude Louis Berthollet in Javel, Paris. The author's reaction that led to the synthesis of said compound is expressed by the following chemical equation:

Cl ₂ + 2KOH => KCl + KClO + H ₂ O

According to the equation, molecular chlorine reacts with potassium hydroxide (or caustic potash), reducing and oxidizing the chlorine atoms. This can be verified by comparing the oxidation number of Cl in KCl (-1) with that of Cl in KClO (+1).

Chemical structure

The upper image represents the electrostatic interactions between the K ⁺ cation and the OCl ^- anion (with oxygen carrying a negative formal charge).

These ions have the same stoichiometric proportions (1: 1) and their non-directional forces form a crystalline arrangement, where the K ⁺ is positioned closest to the O atom.

Although there are no studies that describe the crystal system of KOCl (cubic, orthorhombic, monoclinic, etc.), it is enough to visualize it as a large sphere of K ⁺ attracted towards the ion of linear geometry of OCl ^-.

It can be thought that, unlike NaOCl, KOCl forms crystals with lower lattice energy, because K ⁺ is larger than Na ⁺ compared to OCl ^-. This greater dissimilarity between their ionic radii makes the electrostatic forces present between them less effective.

Also, the performance in aqueous solution for this salt can be expected to be similar to that of NaOCl. Surrounded by water, the K ⁺ -more voluminous- must have a greater hydration sphere than that of Na ⁺. Otherwise, the properties of their solutions (color, smell and whitening power) do not differ to a significant degree.

Nomenclature

Why is the potassium hypochlorite salt so named? To answer this, one must resort to the nomenclature of ternary salts governed by the IUPAC. First of all, because potassium only has a +1 valence, it is unnecessary to write it down; therefore, it is ignored. So, potassium hypochlorite (I) is not written.

Chloric acid has the formula HClO ₃. As the number of oxygens decreases, the chlorine atom gains more electrons; that is, it has less positive oxidation numbers. For example, in this acid Cl has an oxidation number of +5.

As in HClO, Cl has an oxidation number of +1 which, in addition, has two less O atoms (1 instead of 3 compared to HClO ₃), the suffix of its name changes to –oso. Also, since +1 is the smallest oxidation number that the Cl atom can reach, the prefix -hypo is added.

So, HClO is called hypochlorous acid. However, KOCl is its potassium salt and for Cl oxidation numbers less than +5 the suffix –oso is exchanged for the suffix –ito. Otherwise, for oxidation numbers equal to or greater than +5, the suffix is ​​changed to –ato. So, the name remains potassium hypochlorite.

Properties

Molar mass

90.55 g / mol.

Appearance

It is a slightly grayish liquid.

Density

1.16 g / cm ³

Melting point

-2 ° C (28 ° F; 271 ° K). This low melting point, despite the ionic character of its bonds, demonstrates the weak crystalline lattice energy of its pure solid, a product of the monovalent charges of K ⁺ and OCl ^-, and the difference in their ionic radii.

Boiling point

102 ° C (216 ° F; 375 ° K). It is only slightly higher than pure water.

Water solubility

25% w / v, this being a reasonable value given the ease of water molecules to solvate K ⁺ ions.

Aqueous solutions of potassium hypochlorite have bleaching qualities, as do those of NaOCl. It is irritating and can cause severe damage in contact with the skin, eyes and mucous membranes. Likewise, its inhalation produces bronchial irritation, respiratory distress and pulmonary edema.

Reactivity

-Potassium hypochlorite is a powerful oxidizing agent that is not considered an element that causes fires or explosions. However, it is capable of combining with different chemical elements to produce flammable and explosive compounds.

-In contact with urea it can form NCl ₃, a highly explosive compound. When heated or brought into contact with acids, it produces highly toxic chloride smoke. Reacts vigorously with charcoal in a potentially explosive reaction.

-It combines with acetylene to form the explosive chloroacetylene. Likewise, its reaction with organic matter, oil, hydrocarbons and alcohols can cause explosions. Its reaction with nitromethane, methanol and ethanol can become explosive.

-It decomposes releasing oxygen, a process that can be catalyzed by rust or by the metal container that contains it.

-Potassium hypochlorite must be kept cold to avoid the formation of potassium chlorate, whose decomposition can even be explosive.

Applications

-It is used as a disinfectant for surfaces and drinking water.

-The degradation in soils of potassium hypochlorite into potassium chloride has suggested its use in crops as a source of potassium, a primary nutritional element for plants.

-Some companies have suggested its application as a substitute for NaOCl as a bleaching agent, claiming the beneficial properties of the K ⁺ ion compared to the environmental impact caused by Na ⁺.

References

1. Enviro Tech. The Sodium Free Solution.. Retrieved on May 29, 2018, from: envirotech.com
2. PubChem. (2018). Potassium Hypochlorite. Retrieved on May 29, 2018, from: pubchem.ncbi.nlm.nih.gov
3. Wikipedia. (2018). Potassium hypochlorite. Retrieved on May 29, 2018, from: en.wikipedia.org
4. Chemical Book. (2017). Potassium hypochlorite. Retrieved on May 29, 2018, from: chemicalbook.com
5. Whitten, Davis, Peck & Stanley. Chemistry. (8th ed.). CENGAGE Learning, p 873, 874.