Potassium Hydroxide

OVERVIEW

Potassium hydroxide (poe-TAS-ee-yum hy-DROK-side) is a white deliquescent solid that is available in sticks, lumps, flakes, or pellets. A deliquescent material is one that tends to absorb so much moisture from the atmosphere that it becomes very wet, even to the point of dissolving in the water it has absorbed. Potassium hydroxide also absorbs carbon dioxide from the air, changing in the process to potassium carbonate (K₂CO₃). Potassium hydroxide is one of the most caustic materials known. It has a number of uses in industry and agriculture.

Potassium hydroxide is chemically very active. It reacts violently with acids, generating significant amounts of heat in the process. In moist air, it corrodes metals such as tin, lead, zinc, and aluminum with the release of combustible and explosive hydrogen gas.

KEY FACTS

OTHER NAMES:

Caustic potash; potash lye; potassa; potassium hydrate

FORMULA:

KOH

ELEMENTS:

Potassium, oxygen, hydrogen

COMPOUND TYPE:

Base (inorganic)

STATE:

Solid

MOLECULAR WEIGHT:

56.10 g/mol

MELTING POINT:

406°C (763°F)

BOILING POINT:

1327°C (2421°F)

SOLUBILITY:

Soluble in water, ethyl alcohol, methyl alcohol, and glycerol

HOW IT IS MADE

Potassium hydroxide is made by the electrolysis of an aqueous solution of potassium chloride (KCl). In that process, an electric current decomposes potassium chloride into potassium and chlorine. The chlorine escapes as a gaseous by-product and the potassium reacts with water to form potassium hydroxide.

COMMON USES AND POTENTIAL HAZARDS

An estimate 440,000 metric tons (485,000 short tons) of potassium hydroxide were used in the United States in 2005. About 53 percent of that amount was used in the production of other potassium compounds, especially potassium carbonate (28 percent), potassium acetate, potassium cyanide, potassium permanganate, and potassium citrate. About 10 percent of all caustic potash was used in the manufacture of potassium soaps and detergents. Most soaps and detergents are made of sodium hydroxide. But potassium hydroxide can be substituted for sodium hydroxide to obtain soaps and detergents with special properties. Liquid soaps and soaps that will lather in salt water or water with a high mineral content are examples of such specialized potassium soaps.

Some other applications of potassium hydroxide include:

• The manufacture of liquid fertilizers, herbicides, and other agricultural chemicals;
• As a neutralizing agent in many chemical and industrial processes;
• In the production of synthetic rubber;

• In the food production industry, where it is used in the removal of peels from fruits and vegetables, the carmelization of products that contain sugar, the thickening of ice cream, the softening of olives, the production of chocolate and cocoa, and the preparation of hominy from corn kernels;
• In the manufacture of alkaline storage batteries and some types of fuel cells;
• In the refining of petroleum;
• As a way for removing horn buds from young cattle;
• In a number of cosmetic procedures, such as softening of cuticles, removal of warts, and cleaning of dentures; and
• As an ingredient in paint removers.

Interesting Facts

• Pure potassium hydroxide is difficult to prepare since the compound is so reactive that it tends to react with moisture, carbon dioxide, and other impurities with which it comes into contact. The compound is commercially available in a purity of about 90 percent. Much purer products are available, however, when needed.

Potassium hydroxide is a very hazardous chemical. It is corrosive to tissue and can cause severe burns of the skin, eyes, and mucous membranes. If ingested, it can cause internal bleeding, scarring of tissue, nausea, vomiting, diarrhea, and lowered blood pressure that can result in a person's collapse. In sufficient amounts, it can cause death. Inhalation of potassium hydroxide fumes or dust can cause lung irritation, sneezing, sore throat, runny nose, and severe damage to the lungs. In contact with the eyes, the compound can cause blurred vision and, in sufficient amounts, loss of eyesight. People who have to work with the compound should always wear goggles, gloves, and protective clothing to reduce their risk of contact with the chemical.

Words to Know

AQUEOUS SOLUTION

A solution that consists of some material dissolved in water.

CAUSTIC

Strongly basic or alkaline; able to irritate or corrode living tissue.

DELIQUESCENT

Having the tendency to absorb moisture and, therefore, dissolve or melt.

MUCOUS MEMBRANES

Tissues that line the moist inner lining of the digestive, respiratory, urinary and reproductive systems.

FOR FURTHER INFORMATION

"Caustic Potash." Occidental Petroleum Corporation. http://www.oxy.com/OXYCHEM/Products/caustic_potash/caustic_potash.htm (accessed on November 1, 2005).

Cavitch, Susan Miller. The Natural Soap Book: Making Herbal and Vegetable-Based Soaps. Markahm, Canada: Storey Publishing, 1995.

"Potassium Hydroxide." Medline Plus. http://www.nlm.nih.gov/medlineplus/ency/article/002482.htm (accessed on November 1, 2005).

"Potassium Hydroxide." NIOSH Pocket Guide to Chemical Hazards. http://www.cdc.gov/niosh/npg/npgd0523.html (accessed on November 1, 2005).

See AlsoSodium Hydroxide