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Difference Between Potassium Hydroxide and Sodium Hydroxide

Difference Between Potassium Hydroxide and Sodium Hydroxide

Although potassium hydroxide and sodium hydroxide have almost similar properties, one cannot replace the other in certain applications. This ScienceStruck article describes the slight differences between these two compounds.
ScienceStruck Staff
Did You Know?
As sodium hydroxide dissolves oils and fats in skin and flesh, animal disposal contractors use it to dispose off animals that are struck and killed by motor vehicles. It is also an inexpensive and easily available compound.

Potassium hydroxide and sodium hydroxide, common inorganic compounds, are used in various industries to produce their salts (like carbonates and phosphates) and a number of useful chemical compounds. They are hygroscopic and deliquescent, which means, they absorb water from the environment and dissolve in it. When added to water, they generate heat. Both are highly corrosive by nature, and need to be handled carefully.
Being alkaline, they are used to neutralize acids. Both are widely used in the paper industry, petrochemical industry, and food industry (in washing or chemical peeling of fruits and vegetables, and in other food processing techniques). They act as food thickeners and are used as additives; for example, in ice creams. As cleaning agents, they are used to produce detergents and other cleaning solutions (for example, drain cleaners). They are used to dissolve carcasses. Because of the similar properties, they have similar uses, but in certain applications manufacturers have to use only KOH or only NaOH. The potassium hydroxide vs. sodium hydroxide analysis given below serves to elaborate on their differences.
Potassium Hydroxide vs. Sodium Hydroxide
Basic Information
Formula KOH NaOH
Molar Mass 56.1056 g/mol 39.997 g/mol
Density 2.04 g/cm3 2.13 g/cm3
Boiling Point 2,421°F (1,327°C) 2,530°F (1,388°C)
Melting Point 762.8°F (406°C) 604.4°F (318°C)
Common Name Caustic Potash Caustic Soda or Lye
Production Relatively less produced.
Its annual production is about 100 times more than KOH.
Way of Production It is obtained through the electrolysis of its chloride. It is obtained through the electrolysis of sodium chloride.
Conductivity It is more conductive than NaOH. It is less conductive than KOH.
Exothermic KOH and water reaction is slightly less exothermic. NaOH and water reaction is slightly more exothermic.
More soluble in water, methanol, and ethanol than NaOH. 100 g of NaOH dissolves in 100 ml of water. It is soluble in water, methanol, and ethanol. It is insoluble in ether and other non-polar solvents. 121 g of KOH dissolves in 100 ml of water.
Atomic Weight
Potassium has an atomic weight of 39.10 and has 19 protons. This makes the metal in potassium hydroxide heavier than the metal in sodium hydroxide. Sodium has an atomic weight of 22.99, and has only 11 protons. The metal in sodium hydroxide is lighter than the metal in potassium hydroxide.
Color and Form
It comes in the form of white powder or translucent pellets, which become tacky in air because of its water absorbing property (hygroscopic nature). KOH solutions leave a white or translucent stain. It comes in the form of whitish pellets, flakes, granules, and liquid. NaOH solutions leave a yellow stain.
Different Uses
  • KOH is used for soap making, especially liquid soaps, as it needs lesser water to become liquid (the soap contains higher amount of cleaning agent than the soap made with other substances). It is mainly used to produce soft and liquid soaps.
  • It is present in various lotions, shampoos, hairsprays, manicure products, shaving creams, drain cleaners, oven /driveway / concrete cleaners, paint and varnish removers, metal cleaners, etc.
  • KOH test is used to confirm fungal infection on skin.
  • In laboratories, it is used to study insects (after the tissues are dissolved), and to identify certain mushrooms.
  • It is used to remove hair from animal hide.
  • It is used in herbicides, fungicides, and fertilizers.
  • It works as an electrolyte in alkaline batteries.
  • NaOH is mainly used in solid soap bars and detergents, but is also present in other bath products, cleansing products, bleaches, shampoos, and shaving products. It helps control the pH of cosmetics.
  • It is used to clean industrial equipment, storage tanks, waste discharge pipes, etc. It can dissolve grease, oils, fats, and protein-based deposits (it hydrolyzes the proteins present in hair which usually blocks pipes). It is often used to clean ovens and stainless steel / glass bake-ware.
  • Relaxers that are used by professionals to straighten the hair contain NaOH.
  • It is used in the Bayer process of aluminum production.
  • It is used in the purification of the ore, bauxite.
  • People often think that yellow-colored Chinese noodles contain eggs, but actually they don't. They are made with lye-water. Chinese moon cake crust also contains lye-water.

Manufacturers usually prefer sodium hydroxide over potassium hydroxide because it is cheaper. Sometimes, NaOH is preferred because a smaller quantity (as compared to KOH) serves the purpose. The biggest difference between them is the cost, because the cost of NaOH production (from sodium chloride, common salt, which is quite inexpensive) can be around ⅓ of the cost of KOH production.