KOH — Potassium Hydroxide
Potassium hydroxide (KOH), commonly known as caustic potash, is a strong alkali used in chemical manufacturing, soap production, batteries, fertilizers, and laboratory applications.
Interactive 3D Molecular Structure — KOH
Properties
| Chemical Formula | KOH |
|---|---|
| Molecular Mass | 56.11 g/mol |
| Physical State | Solid (Crystalline or Flakes) |
| Melting Point | 360°C |
| Boiling Point | 1320°C (decomposes) |
| Density | 2.12 g/cm³ |
| pH | 13–14 (1 M solution) |
| Odor | Odorless |
| Color | White or colorless |
| Taste | Bitter and soapy (corrosive, not for tasting) |
| Polarity | Ionic |
| Type of Bond | Ionic (K⁺ and OH⁻) |
Introduction to Potassium Hydroxide
Potassium hydroxide (KOH) is an inorganic compound commonly referred to as caustic potash or lye. It is a highly corrosive and hygroscopic base that absorbs moisture and carbon dioxide from the air. KOH is one of the strongest known bases, similar in behavior to sodium hydroxide (NaOH), and it readily dissociates in water to produce hydroxide ions \(OH^-\).
Potassium hydroxide is a critical compound in many industries including soap manufacturing, fertilizer production, chemical synthesis, battery production, and biodiesel processing. Due to its strong alkalinity, it is also used in laboratories for neutralization reactions, pH control, and titrations.
Structure and Bonding
Potassium hydroxide is composed of potassium cations (K⁺) and hydroxide anions (OH⁻) held together by ionic bonds. The potassium ion carries a positive charge, while the hydroxide ion carries a negative charge, creating an electrostatic attraction between them. In aqueous solution, KOH dissociates completely:
\(KOH \rightarrow K^+ + OH^-\)
The hydroxide ions impart strong basic properties to the solution, making it highly reactive with acids and other compounds. Solid KOH has a crystalline structure and is very soluble in water and alcohols, releasing heat when dissolved (an exothermic reaction).
Preparation of Potassium Hydroxide
Potassium hydroxide is primarily produced through the electrolysis of potassium chloride (KCl) solution using the Chlor-Alkali Process. This process is similar to that used for the preparation of sodium hydroxide. The reaction can be represented as:
\(2KCl + 2H_2O \xrightarrow{Electrolysis} 2KOH + Cl_2 + H_2\)
In this process, chlorine gas is released at the anode, hydrogen gas at the cathode, and potassium hydroxide is formed in the solution. The resulting solution is concentrated by evaporation to obtain solid KOH flakes or pellets.
Alternatively, potassium hydroxide can be produced by reacting potassium carbonate (K₂CO₃) with calcium hydroxide (Ca(OH)₂), followed by filtration and evaporation:
\(K_2CO_3 + Ca(OH)_2 \rightarrow 2KOH + CaCO_3\)
Physical and Chemical Properties
- Physical State: White, deliquescent solid that absorbs moisture and carbon dioxide from the air.
- Solubility: Highly soluble in water and alcohol; dissolution is exothermic.
- Reactivity: Strongly reacts with acids, organic compounds, and some metals.
- Thermal Stability: Stable at room temperature but decomposes at high temperatures.
- Reaction with Acids: Neutralizes acids to form potassium salts and water.
- Reaction with CO₂: Absorbs carbon dioxide to form potassium carbonate.
- Reaction with Amphoteric Metals: Reacts with aluminum and zinc to liberate hydrogen gas.
\(KOH + HCl \rightarrow KCl + H_2O\)
\(2KOH + CO_2 \rightarrow K_2CO_3 + H_2O\)
\(2Al + 2KOH + 6H_2O \rightarrow 2K[Al(OH)_4] + 3H_2\)
Uses and Applications of Potassium Hydroxide
- Soap and Detergent Manufacturing: KOH is used in the saponification of fats and oils to produce soft soaps that remain liquid at room temperature, unlike sodium-based soaps.
- Biodiesel Production: Serves as a catalyst in the transesterification of vegetable oils to biodiesel.
- Battery Industry: Used as an electrolyte in alkaline batteries due to its high ionic conductivity.
- Food Industry: Used as a food additive (E525) for pH regulation and as a peeling agent for fruits and vegetables.
- Agriculture: Acts as a neutralizer and in fertilizer formulation to adjust soil acidity.
- Chemical Manufacturing: Used in the production of potassium phosphates, potassium soaps, and potassium salts.
- Water Treatment: Employed in neutralizing acidic waste and purifying drinking water.
Health and Safety Precautions
Potassium hydroxide is highly caustic and should be handled with extreme care. Direct contact can cause severe burns, tissue damage, and eye injury. It reacts violently with acids and organic materials, releasing heat. Always wear protective gloves, goggles, and a lab coat while handling KOH.
In case of skin or eye contact, the affected area should be flushed immediately with water for at least 15 minutes. If ingested, it can cause serious internal injury. KOH should be stored in airtight, corrosion-resistant containers away from moisture, acids, and oxidizing agents.
Despite its hazards, potassium hydroxide remains one of the most versatile industrial bases due to its strong reactivity and wide application range.
Key Reactions of Potassium Hydroxide
Neutralization Reaction with Hydrochloric Acid
Potassium hydroxide neutralizes hydrochloric acid to produce potassium chloride and water:
\(KOH + HCl \rightarrow KCl + H_2O\)
This reaction is widely used in titrations and industrial salt manufacturing.
Reaction with Carbon Dioxide
Potassium hydroxide reacts readily with carbon dioxide to form potassium carbonate:
\(2KOH + CO_2 \rightarrow K_2CO_3 + H_2O\)
This property allows it to be used in air purification systems to remove CO₂ from enclosed spaces such as submarines and spacecraft.
Reaction with Aluminum
Potassium hydroxide reacts with aluminum metal in the presence of water to produce potassium aluminate and hydrogen gas:
\(2Al + 2KOH + 6H_2O \rightarrow 2K[Al(OH)_4] + 3H_2\)
This is an example of an amphoteric metal reaction, showcasing KOH’s strong base properties.