Potassium Chloride (KCl)

Table of Contents

• • What is Potassium Chloride?
  • Medicinal Use of Potassium Chloride
  • Preparation of Potassium Chloride
  • Structure of KCl Molecules
  • Properties of Potassium Chloride
  • Uses of Potassium Chloride
  • Frequently Asked Questions

What is Potassium Chloride?

Potassium chloride is an ionic salt featuring a bond between an alkali metal and a halogen. It is denoted by the chemical formula KCl and is made up of potassium cations and chloride anions in a 1:1 ratio.

Potassium chloride is characterized by a colourless, crystalline appearance and an odourless smell. In its solid form, potassium chloride can be easily dissolved in water and the resulting KCl solution is said to have a salty taste.

The primary application of this ionic salt is in the agriculture industry, where it is used in the production of crop fertilizers. Potash, a water-soluble crystalline material that is used for fertilization, can be prepared from potassium chloride (and some other minerals). This compound is also used as a substitute for common salt (sodium chloride) in food. Oral consumption of appropriate quantities of KCl can help treat low blood potassium in humans. 

Medicinal Use of Potassium Chloride

In the human body, potassium is essential for several vital functions to occur, the most notable of which is the beating of the heart.  Dangerously low levels of potassium in the body can, therefore, prove fatal. The condition in which the levels of potassium in the blood become very low is called hypokalemia. This condition can occur due to the use of certain medication or due to certain diseases. For example, an individual may develop hypokalemia during or after a prolonged illness which is accompanied by vomiting and/or diarrhoea.

Potassium chloride is a great source of potassium and is, therefore, used to treat hypokalemia. In fact, it can even be taken to prevent hypokalemia. Potassium chloride is usually prescribed in the form of a capsule or a tablet. It can also be administered orally in the liquid form. It is important to note that potassium chloride must not be administered to individuals suffering from hyperkalemia (a condition where the blood potassium levels are elevated).

Preparation of Potassium Chloride

Potassium chloride can be directly extracted from some minerals such as carnallite, sylvite, and potash. This compound can also be extracted from seawater. KCl is produced as a by-product during the synthesis of nitric acid from hydrochloric acid and potassium nitrate. 

In the laboratory, KCl can be prepared by reacting bases of potassium (such as potassium hydroxide) with hydrochloric acid. The ensuing acid-base neutralization reaction will yield water and potassium chloride as the products.

Structure of KCl Molecules

An illustration describing the structure of a KCl molecule is provided below.

Structure of Potassium Chloride

The type of chemical bond that holds together the potassium and chlorine atoms in a potassium chloride molecule is an ionic bond. The electronegative chlorine atom accepts the 4s electron belonging to the potassium atom and an ionic attraction arises between the resulting K⁺ and the Cl^– ions.

Properties of Potassium Chloride

In the solid-state, KCl is readily soluble in many polar solvents, including water. The salt is ionized into the K⁺ cation and the Cl^– anions in these polar solvents. Some other physical and chemical properties of potassium chloride are discussed in this subsection.

Physical Properties

• • • • The crystals of potassium chloride are made up of face-centred cubic (FCC) unit cells.
      • The molar mass of KCl is 74.5513 grams/mol.
      • Its density in the solid, crystalline form is 1.984 grams per cubic centimetre.
      • The melting and boiling points of potassium chloride are 1040 K and 1690 K respectively.
      • At 0^oC, 20^oC, and 100^oC, the solubility of KCl in water corresponds to 217.1 g/L, 253.9 g/L, and 360.5 g/L respectively.
      • Potassium chloride is highly soluble in alcohols but not soluble in ether (organic compounds with the formula R-O-R’).

Chemical Properties

• • • • Since potassium chloride is completely ionized into K⁺ and Cl^– ions in water, the resulting aqueous solution exhibit high values of electrical conductivity.
      • The reduction of potassium chloride into metallic can be achieved with the help of metallic sodium, despite the lower electropositivity of sodium when compared to potassium.
      • This is achieved by heating the KCl with metallic sodium to a temperature of 850 ^o
      • The chemical equation for this reaction is: KCl + Na ⇌ NaCl + K

It can be noted that when the solid form of potassium chloride is subjected to a flame test, it burns with a pale violet or a lilac-coloured flame, as is the case with most other potassium-containing compounds.

Uses of Potassium Chloride

Potassium chloride has a wide range of medical and industrial applications. It is also an integral part of fertilizer production. Some important uses of KCl are listed below.

• • • • Potassium chloride is used in the manufacture of potash, an important form of fertilizer that enriches soils with potassium which promotes the growth of plant life. Potassium availability is usually the key inhibitor for plant growth. Potassium chloride, acting as a source of potassium, can increase the availability of potassium in the soil.
      • The potash fertilizers made from KCl (called Muriate of Potash, or MOP) make up the majority of potash fertilizers sold worldwide.
      • The medical treatment of low blood pressure commonly employs potassium chloride as a part of the medication.
      • KCl is used as a salt substitute in food where a low concentration of sodium in the salt is desired in order to reduce the risk of high blood pressure.
      • Potassium chloride is one of the important raw materials required in the manufacture of potassium metal.
      • The metal halide salt KCl is also used in the manufacture of soaps. Water softening units can involve the use of potassium chloride as an alternative to sodium chloride as well.
      • The use of potassium chloride as a source of beta radiation is extremely useful in calibrating radiation monitoring equipment.
      • The flux required in the oxy-fuel welding of aluminium consists of potassium chloride along with the chloride salts of lithium and sodium.

Potassium chloride has the potential to be used as a fire extinguishing agent was initially used in portable and wheeled fire extinguishers. It was referred to as the Super-K dry chemical and was known to be more effective when compared to sodium bicarbonate-based dry chemicals for this purpose. Furthermore, potassium chloride is known to be compatible with protein foam. However, the use of potassium chloride for this purpose gradually reduced with the introduction of potassium bicarbonate (also referred to as Purple-K) dry chemical towards the end of the 1960s. Purple-K was found to be far less corrosive (and more effective) than potassium chloride for this purpose.

Thus, the various physical and chemical properties of potassium chloride are discussed along with its uses. To learn more about potassium chloride and other potassium compounds such as potassium chlorate, register with BYJU’S and download the mobile application on your smartphone.