Potassium Hydroxide: Definition, Formula, Preparation, Properties & Uses

Potassium hydroxide is an alkali metal hydroxide. It is an inorganic compound with the chemical formula \({\rm{KOH}}.\) It is commonly known as caustic potash, lye, potash lye and potassia. Like sodium hydroxide, potassium hydroxide is also a prototypical strong base. As potassium hydroxide is a strong base, it is marketed in various forms such as pellets, powders, and flakes. In this article, we are going to discuss more about potassium hydroxide.

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Potassium Hydroxide (KOH): Details

The chemical formula of potassium hydroxide is \({\rm{KOH}}.\) It contains potassium \(\left( {{{\rm{K}}^{\rm{ + }}}} \right)\) ion and hydroxyl \(\left( {{\rm{O}}{{\rm{H}}^{\rm{ – }}}} \right)\) ions. The bond formed between this potassium \(\left( {{{\rm{K}}^{\rm{ + }}}} \right)\) ion and hydroxyl \(\left( {{\rm{O}}{{\rm{H}}^{\rm{ – }}}} \right)\) ions is an ionic bond. Therefore, it is considered as an ionic compound. Solid potassium hydroxide \(\left( {{\rm{KOH}}} \right)\) has a rhombohedral crystal structure. Potassium hydroxide \(\left( {{\rm{KOH}}} \right)\) can be represented as,

The molar mass of potassium hydroxide \(\left( {{\rm{KOH}}} \right)\) is \(56.11\;{\rm{g}}/{\rm{mol}}.\)

Potassium Hydroxide (KOH): Preperations

In ancient times, potassium hydroxide is made by the reaction of potassium carbonate with a strong solution of slaked lime (calcium hydroxide). The chemical equation for the reaction can be given as,

\({\rm{Ca}}{({\rm{OH}})_2} + {{\rm{K}}_2}{\rm{C}}{{\rm{O}}_3} \to {\rm{CaC}}{{\rm{O}}_3} + 2{\rm{KOH}}\)

The above reaction is an example of a double displacement or salt metathesis reaction.

The above method was replaced by a new method which involves the electrolysis of potassium chloride solutions. As a result, potassium hydroxide is produced. This process results in the production of chlorine (at the anode) and hydrogen (at the cathode) gas as a byproduct. That is,

\(2{\rm{KCl}} + 2{{\rm{H}}_2}{\rm{O}} \to 2{\rm{KOH}} + {\rm{C}}{{\rm{l}}_2} + {{\rm{H}}_2}\)

The above method is similar to the preparation of sodium chloride by Chloralkali process.

Potassium Hydroxide (KOH): Properties

Let us discuss the physical and chemical properties of potassium hydroxide \(\left( {{\rm{KOH}}} \right).\)

Potassium Hydroxide (KOH): Physical Properties

1. Potassium hydroxide appears as a white solid. It is odourless too.
2. It is a deliquescent (a substance that absorbs moisture from air and becomes a liquid) and a hygroscopic (a substance that has the ability to absorb water from the surrounding environment) substance. 
3. It is soluble in water, alcohol and glycerol. It is insoluble in ether and liquid ammonia.
4. A solution of potassium hydroxide in ethanol is generally called as ethanolic potassium hydroxide. 
5. It has a melting point approximately equal to \({\rm{633}}\,{\rm{K}}\) and a boiling point approximately equal to \({\rm{1600}}\,{\rm{K}}{\rm{.}}\)

Potassium Hydroxide (KOH): Chemical Properties

1. Potassium hydroxide dissolves in water to form a strongly alkaline solution. 
2. Potassium hydroxide is a strong base. Therefore, it reacts with acids to form salt and water as the products. Such reactions are called as neutralization reactions.

Reaction of Potassium Hydroxide with Sulphuric Acid

Potassium hydroxide reacts with sulphuric acid to form potassium sulphate and water. The chemical equation for the reaction can be given as,

\({{\rm{H}}_2}{\rm{S}}{{\rm{O}}_4} + 2{\rm{KOH}} \to {{\rm{K}}_2}{\rm{S}}{{\rm{O}}_4} + 2{{\rm{H}}_2}{\rm{O}}\)

Reaction of Potassium Hydroxide with Hydrochloric Acid

Potassium hydroxide reacts with hydrochloric acid to form potassium chloride and water. The chemical equation for the reaction can be given as,

\({\rm{KOH}} + {\rm{HCl}} \to {\rm{KCl}} + {{\rm{H}}_2}{\rm{O}}\)

Reaction of Potassium Hydroxide with Nitric Acid

Potassium hydroxide reacts with nitric acid to form potassium nitrate and water. The chemical equation for the reaction can be given as,

\({\rm{HN}}{{\rm{O}}_3} + {\rm{KOH}} \to {\rm{KN}}{{\rm{O}}_3} + {{\rm{H}}_2}{\rm{O}}\)

3. Other Reactions of potassium hydroxide

Reaction of Potassium Hydroxide with Carbon Dioxide

Potassium hydroxide reacts with carbon dioxide to form potassium bicarbonate. The chemical equation for the reaction can be given as,

\({\rm{KOH}} + {\rm{C}}{{\rm{O}}_2} \to {\rm{KHC}}{{\rm{O}}_3}\)

Reaction of Potassium Hydroxide with Zinc Metal

Potassium hydroxide reacts with zinc metal to form potassium zincate along with the liberation of hydrogen gas. The chemical equation for the reaction can be given as,

\({\rm{Zn}} + 2{\rm{KOH}} \to {{\rm{K}}_2}{\rm{Zn}}{{\rm{O}}_2} + {{\rm{H}}_2}\)

Reaction of Potassium Hydroxide Solution with Aluminium Metal

Aluminium reacts with concentrated potassium hydroxide solution to form potassium aluminate along with the evolution of hydrogen gas. The chemical equation for the reaction can be given as,

\(2{\rm{Al}} + 2{\rm{KOH}} + 6{{\rm{H}}_2}{\rm{O}} \to {\rm{K}}\left[ {{\rm{Al}}{{({\rm{OH}})}_4}} \right] + 3{{\rm{H}}_2}\)

Reaction of Potassium Hydroxide with Copper Sulphate

Potassium hydroxide reacts with copper sulphate to form potassium sulphate and copper hydroxide. The chemical equation for the reaction can be given as,

\({\rm{CuS}}{{\rm{O}}_4} + 2{\rm{KOH}} \to {\rm{Cu}}{({\rm{OH}})_2} + {{\rm{K}}_2}{\rm{S}}{{\rm{O}}_4}\)

Potassium Hydroxide (KOH): Uses

Potassium hydroxide has got many uses. They include: 

1. Potassium hydroxide is used as a precursor to other potassium compounds. That is, several potassium salts can be produced by the neutralization reactions involving potassium hydroxide.
2. It is used for the manufacture of soft potassium soaps. That is, the saponification reaction of fats with potassium hydroxide produces potassium soaps which are soft in nature.
3. In alkaline batteries, aqueous potassium hydroxide is used as an electrolyte.
4. Potassium hydroxide is used as a food thickener, food stabilizer and as a \({\rm{pH}}\) controlling agent.
5. Potassium hydroxide is used in semiconductor chip fabrication.
6. In manicure treatments, potassium hydroxide is used as an active ingredient in cuticle remover.
7. It is used for the removal of hairs from animal hides.
8. Potassium hydroxide is used for the identification of certain special species of fungi.
9. It is used in paint and varnish removers.
10. Potassium hydroxide is also used in liquid drain cleaners.

Summary

Potassium hydroxide is an alkali metal hydroxide with the chemical formula \({\rm{KOH}}{\rm{.}}\) It is commonly known as caustic potash. It is a strong base like sodium hydroxide. It is marketed in various forms such as pellets, powders, and flakes. It is majorly produced by the electrolysis of potassium chloride solutions. It has got many uses too. In this article, we have included its preparation methods, physical and chemical properties, and its various uses.

Frequently Asked Questions on Potassium Hydroxide (KOH)

Frequently asked questions related to potassium hydroxide is listed as follows:

Q. What is the formula of potassium hydroxide?
Ans: Potassium hydroxide is an inorganic chemical compound with the formula \({\rm{KOH}}{\rm{.}}\) It is a strong base.

Q. What is potassium hydroxide used for?
Ans: Potassium hydroxide has got many uses. It is used as a precursor to other potassium compounds, manufacture of soft potassium soaps, as an electrolyte in alkaline batteries, food thickener, \({\rm{pH}}\) control agent, liquid drain cleaners, etc.

Q. Is potassium hydroxide harmful to humans?
Ans: Yes, the skin or eye contact with potassium hydroxide solutions can cause burns, severe irritation, and even blindness. Inhalation of higher concentrations of potassium hydroxide can cause lung damage. The swallowing of potassium hydroxide may cause severe burns of the mouth, throat, and stomach.

Q. Is potassium hydroxide a strong base?
Ans: Yes, like sodium hydroxide, potassium hydroxide is a strong base. A strong base completely ionises in water and produces a large amount of hydroxide \(\left( {{\rm{O}}{{\rm{H}}^ – }} \right)\) ions.

Q. What is meant by ethanolic potassium hydroxide?
Ans: A solution of potassium hydroxide in ethanol is generally called ethanolic potassium hydroxide.

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