1310-58-3 Usage
Reactions
Potassium hydroxide is a very strong base, more basic than caustic soda. It is neutralized by acids. The solution on evaporation yields the corresponding potassium salt:
KOH + HCl → K+ + Cl¯+ H2O
Action of bromine or iodine on a warm concentrated solution of KOH forms bromate and bromide or iodate and iodide, respectively:
3Br2 + 6OH¯→ BrO3¯ + 5Br¯ + 3H2O
3I2 + 6OH¯ → IO3¯ + 5I¯ + 3H2O
When carbon dioxide is passed through its aqueous solution and the solution evaporated, potassium bicarbonate is formed:
KOH + CO2 → KHCO3
Reaction with carbon monoxide at 100 to 200°C at a CO pressure above 7 atm yields potassium formate:
KOH + CO → HCOOK
Reaction with phenol in dilute methanol solution forms potassium phenoxide:
KOH + C6H5OH → C6H5OK + H2O
Reaction with boric acid and hydrofluoric acid forms potassium tetrafluoroborate, KBF4:
KOH + H3BO3 + 4HF → KBF4 + 4H2O
An alcoholic solution of potassium hydroxide reacts with an alcoholic solution of carbon disulfide to form potassium ethylxanthogenate, C2H5OCS2K
KOH + C2H5OH + CS2 → C2H5OCS2K + H2O
Reaction with sodium borohydride forms potassium borohydride:
POTASSIUM HYDROXIDE 759KOH + NaBH4 → KBH4 + NaOH
Reaction with hydrofluoric acid forms potassium bifluoride:
KOH + 2HF → KHF2 + H2O
Half neutralization of a phthalic anhydride solution forms potassium hydrogen phthalate.
Purification Methods
Its carbonate content can be reduced by rinsing KOH sticks rapidly with water prior to dissolving them in boiled out distilled water. Alternatively, a slight excess of saturated BaCl2 or Ba(OH)2 can be added to the solution which, after shaking well, is set aside so that the BaCO3 is allowed to separate out. Davies and Nancollas [Nature 165 237 1950] rendered KOH solutions carbonate free by ion exchange using a column of Amberlite IR-100 in the OH-form.
Description
Potassium hydroxide(KOH) is highly basic, forming strongly alkaline solutions in water and other polar solvents. These solutions are capable of deprotonating many acids, even weak ones.
Potassium hydroxide is used to make soft soap, in scrubbing and cleaning operations, as a mordant for woods, in dyes and colorants, and for absorbing carbon dioxide. Other principle uses of caustic potash are in the preparation of several potassium salts, acid-base titrations, and in orgainic sytheses.
Also, KOH is an electrolyte in certain alkaline storage batteries and fuel cells. Potassium hydroxide is used in neutralization reactions to yield potassium salts. Aqueous potassium hydroxide is employed as the electrolyte in alkaline batteries based on nickel-cadmium and manganese dioxide-zinc. Alcoholic KOH solutions are also used as an effective method for cleaning glassware. KOH works well in the manufacture of biodiesel by catalyzing transesterification of the triglycerides in vegetable oil.
Uses
Pharmaceutic aid (alkalizing agent).
Health Hazard
Causes severe burns of eyes, skin, and mucous membranes.
Potassium hydroxide is a strongly alkaline, hydrophilic substance and therefore solid potassium hydroxide is highly corrosive. It reacts with fat and can cause irreversible damage to any site of contact with the body (for example skin or eyes). Solutions of potassium hydroxide in water at concentrations above 0.5% (w/w) are irritating at points of contact and, at higher concentrations, the solutions can be corrosive. Potassium hydroxide does not cause skin allergies. Because of the corrosive properties of potassium hydroxide, its ingestion can be fatal. Under normal conditions of handling and use, potassium hydroxide in solution will dissociate into its constituent ions and, if ingested, will not be systemically available in the body as such.
Chemical Properties
Pure potassium hydroxide is a solid at room temperature, though it is often sold as a liquid. Potassium hydroxide is a strong alkaline substance that dissociates completely in water into the potassium ion (K+) and hydroxide ion (OH-). The dissolution in water generates heat, so a vigorous reaction can occur when potassium hydroxide is added to water. The vapor pressure of the substance is very low and the melting point is high. Potassium hydroxide solutions attack aluminium and its alloys under formation of hydrogen gas. It can be neutralised with acids (e.g. hydrochloric acid) giving the corresponding potassium salts of the acids, which are usually pH neutral and non-corrosive.
Fire Hazard
Non-combustible, substance itself does not burn but may decompose upon heating to produce corrosive and/or toxic fumes. Some are oxidizers and may ignite combustibles (wood, paper, oil, clothing, etc.). Contact with metals may evolve flammable hydrogen gas. Containers may explode when heated.
Production Methods
Potassium hydroxide is produced commerically by electrolysis of a saturated solution of potassium chloride in brine using mercury cells consisting of a titanium anode and mercury cathode. Potassium reacts with mercury forming the amalgam which, on treatment with water, forms potassium hydroxide and hydrogen.
Other types of electrolytic cells, although not so commonly used today, are also known. In a diaphragm type cell that separates the cell into anode and cathode compartments, an aqueous solution of potassium chloride is electrolyzed. Potassium hydroxide and hydrogen are produced at the cathode and chlorine is liberated at the anode. The solution discharged from the cell is evaporated to concentrate potassium hydroxide and precipitate potassium chloride.
Potassium hydroxide also may be made by reacting potassium superoxide with water:
2KO2 + 2H2O → 2KOH + H2O2 + O2
Uses
Potassium hydroxide has many different functions and uses.
- It is primarily used as an intermediate in industrial manufacturing processes, such as the manufacture of fertilisers, potassium carbonate or other potassium salts and organic chemicals.
- It is also used in the manufacture of detergents and in alkaline batteries.
- Small-scale uses include drain cleaning products, paint removers and degreasing agents.
- manufacture of liquid soap;
- mordant for wood;
- absorbing CO2;
- mercerizing cotton;
- paint and varnish removers;
- electroplating, photoengraving and lithography;
- printing inks;
- in analytical chemistry and in organic syntheses.
- Pharmaceutic aid (alkalizer).
Reactivity Profile
POTASSIUM HYDROXIDE absorbs moisture readily forming caustic solution that attacks aluminum and zinc. A piece of potassium hydroxide causes liquid chlorine dioxide to explode [Mellor 2:289. 1946-47]. 1,2-dichloroethylene and potassium hydroxide forms chloroacetylene, which is explosive and spontaneously flammable in air. Potassium hydroxide is highly toxic [Rutledge 1968. p. 134]. A reaction between n-nitrosomethylurea and potassium hydroxide in n-butyl ether resulted in an explosion due to the formation of diazomethane [Schwab 1972]. Potassium persulfate and a little potassium hydroxide and water ignited a polythene (polyethylene) liner of a container by release of heat and oxygen [MCA Case History 1155. 1955]. Using potassium hydroxide to dry impure tetrahydrofuran, which contains peroxides, may be hazardous. Explosions have occurred in the past. Sodium hydroxide behaves in a similar way as potassium hydroxide [NSC Newsletter Chem. Soc. 1967]. A strong base. Forms caustic solution in water. [Merck 11th ed. 1989].
Air & Water Reactions
Hydrolysis generates enough heat to ignite adjacent combustible material [Haz. Chem. Data 1966]. Dissolves in water (with liberation of heat, may steam and spatter. Solution is basic (alkaline). Deliquescent
General Description
A white solid. Corrosive to metals and tissue. Used in soap manufacture, bleach, as an electrolyte in alkaline batteries, and as a food additive.
Applications
| Industry |
Application |
Role/benefit |
| Chemical manufacturer |
Manufacturer of other potassium compounds |
Precursor/source of potassium |
| Electrochemistry |
Manufacture of batteries and fuel cells |
Electrolyte/ good conductors of electricity |
| Wet processing of semiconductors |
Etchant/corrosivity and alkalinity |
| Biomass fuels |
Manufacturing biodiesel from oils and fats |
Catalyst/KOH works well in the manufacture of biodiesel by transesterification of the triglycerides in vegetable oil |
| Food |
Rinse or chemical peel for fruits and vegetables |
Additive in rinse solution/corrosivity and alkalinity |
| Chocolate,cocoa,soft drink,ice cream,etc. |
Stabilizer,thickener and pH regulator |
| Cleaning |
Manufacture of "potassium soaps" |
Saponification agent/has better softness and greater solubility than sodium soaps |
| Industrial cleaners for oven,drain,driveway,concrete,pipe,etc. |
Additive/alkalinity and good solubility for grease |
| Liquid soaps, lotions, shampoos, hairsprays, and denture cleaners |
Additive/helps to increase softness and solubility |
| Medicine |
Disbudding calves horns and dissolving scales and hair in veterinary medicine |
Dissolving solution/good solubility for keratin |
| Dissolving warts and cuticles in humans |
| Diagnose fungal infections |
Diagnose agent |
| Production of potassium boron hydrogen, spironolactone, progesterone and testosterone propionate, etc. |
Raw material |
| Agriculture |
Potassium fertilizers (potassium phosphate) |
Raw material/source of potassium |
| Paper |
Separation of lignin from cellulose fibers |
Additive/alkalinity |
| Dyeing |
Manufacture of tripolycyanamide dye |
Raw material |
| Textile |
Dyeing, bleaching and mercerizing textiles |
Additive/corrosivity and alkalinity |
| Manufacture of artificial fiber and polyester fiber |
Main raw material |
| Chemical analysis |
Titration of acids |
Titration agent/alkalinity |
| Others |
Bleaching textiles |
Bleaching agent |
| Absorption of CO2, SO3 and NO3 in gas streams |
Absorption agent/alkalinity |
| Absorption of H2O |
Absorption agent/ hygroscopicity of anhydrous potassium hydroxide |
