NaOH and KOH are two strong bases widely used across many modern industries. Photo: KPTCHEM.
This article is shared by experts from KPTCHEM - a supplier of NaOH, KOH, and various industrial chemicals with a wide range of concentrations suitable for different applications. With a commitment to prioritizing credibility, all chemical products under the KPTCHEM brand are tested, quality-assured, and accompanied by transparent documentation of origin.
Among the most commonly used strong alkaline compounds today, sodium hydroxide (NaOH) and potassium hydroxide (KOH) are two familiar names that always hold leading importance. Although both are strong bases with many similar properties, they still possess significant differences in structure, reactivity, applications, and their forms in industrial use. Understanding these differences is essential to help you choose the most suitable option for your specific industrial processes.
Similarities between NaOH and KOH
Both of these compounds are alkali metal hydroxides. In solid form, they appear as white flakes or powders. Like many compounds widely used in practice, potassium hydroxide and sodium hydroxide also have common names that you may already be familiar with. Sodium hydroxide is often known as caustic soda, while potassium hydroxide is commonly referred to as caustic potash or potassium caustic. Among them:
Sodium Hydroxide (NaOH)
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Molecular weight: 40 g/mol
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Appearance: White solid, highly hygroscopic
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Melting point: 318°C
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Boiling point: 1,388°C
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Solubility: Highly soluble in water and releases a large amount of heat when dissolved
The name “caustic soda” for NaOH is tied to the historical production method of this compound. In the past, alkali was produced by extracting from soda ash or plant ashes, resulting in a crude alkaline solution with strong corrosive properties, hence the name “caustic soda.” Today, NaOH is manufactured through the electrolysis of sodium chloride (table salt) with much higher purity, yet the traditional name is still retained as it accurately reflects its hazardous nature.
Potassium Hydroxide (KOH)
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Molecular weight: 56.11 g/mol
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Appearance: White solid, strongly absorbs CO₂ and moisture
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Melting point: 360°C
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Boiling point: 1,327°C
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Solubility: Highly soluble in water, but releases less heat than NaOH when dissolved
The term “caustic potash” originates from the word potash (meaning potassium) and the strongly corrosive nature of this compound, which is why it is also known as potassium caustic. Historically, KOH was produced from ash of potassium-rich plants, where a crude alkaline solution was obtained by leaching the ash in boiling pots. In modern industrial processes, potassium hydroxide is refined through the electrolysis of potassium chloride. Its corrosive nature remains extremely strong; in fact, in many reactions, KOH can be even more reactive than NaOH because potassium ions have a larger size and higher mobility.
The association with the term “caustic” comes from the extremely corrosive nature of both substances. When in contact with organic tissues, these compounds can destroy protein and lipid structures, while also causing saponification on the skin surface. Therefore, even a small drop of solution falling onto moist skin can cause deep burns and severe damage. For this reason, protective equipment and strict safety procedures must always be prioritized when working with these chemicals.
Overall, both NaOH and KOH are classified as “caustic” substances because they have very high pH, readily absorb moisture from the air, react violently and release significant heat when dissolved in water, and can cause severe injuries upon direct contact. Although they share many similarities and are produced using similar methods, the difference between Na⁺ and K⁺ ions results in distinct properties. Understanding these differences along with each compound’s advantages and limitations is crucial to selecting the most suitable product for your specific application.
Key differences between NaOH and KOH
Although both caustic soda and caustic potash belong to the group of strong bases and share many similar chemical properties, their ionic structure, reactivity level, and application range reveal very distinct characteristics.
Molecular weight and ionic structure
Sodium hydroxide and potassium hydroxide appear very similar, yet they are fundamentally different. Sodium has 11 protons while potassium has 19 protons. Potassium is larger and heavier, which explains the significant difference in their atomic masses. Specifically, KOH has a molecular weight of 56.106 g/mol, which is much higher than the 39.997 g/mol of NaOH.
However, the real distinction begins at the molecular level. While both are strong bases, their ion sizes and properties differ. The K⁺ ion has a larger radius than the Na⁺ ion, giving it greater mobility in solution. This higher mobility allows reactions involving KOH to occur faster and more completely, especially in processes that interact with organic compounds. The molecular characteristics of potassium hydroxide also allow it to disperse and break down oil molecules more effectively than sodium hydroxide. For this reason, KOH is preferred in applications that require efficient breakdown of fats or organic residues, such as liquid soap production or specialized cleaning processes.
Solubility and heat release
Although their solubility in water at room temperature is nearly the same, NaOH releases much more heat when dissolved. This can lead to sudden temperature spikes and splashing hazards if handled improperly. In contrast, KOH dissolves with less heat release but has even higher solubility, especially as water temperature increases. This makes KOH easier to control and suitable for systems that require stable temperatures or reactions sensitive to heat.
Reaction strength
KOH tends to react more strongly in certain environments due to the larger and more mobile K⁺ ion. Therefore, KOH is often selected for industries requiring high and stable reactivity such as alkaline batteries, liquid soap production, and biodiesel manufacturing. On the other hand, NaOH is preferred in heavy industries like oil treatment, paper production, solid detergent manufacturing, and acid neutralization due to its cost-effectiveness and efficiency on a large scale.
Cost and availability
Sodium hydroxide is produced from sodium chloride, a very abundant and inexpensive raw material. As a result, NaOH has a much more competitive price and is the top choice in industries with high consumption levels.
Potassium salts such as potassium chloride (KCl) are significantly more expensive, so KOH typically costs about three times more than NaOH on a per-ton basis. Because of this, KOH is often used in specialized fields where its superior properties provide real practical value, such as pharmaceuticals, cosmetics, and high-purity chemical applications.
Practical applications of NaOH and KOH
NaOH and KOH are rarely interchangeable because each has its own strengths. NaOH is most suitable for products that require hardness, durability and strong alkalinity in solid forms, such as bar soap, industrial detergents or metal treatment solutions. NaOH is also used for unclogging drains. Meanwhile, KOH is preferred for products that require softness, high solubility or stability in liquid environments, including shampoos, liquid soaps and electrolyte solutions in alkaline batteries.
If you need to clean metal surfaces covered with hardened grease, potassium hydroxide with hot water is the best choice. For thick or softer grease layers, sodium hydroxide can clean effectively at lower cost and with lower water temperature because it releases more heat when dissolved.
In addition, sodium hydroxide and potassium hydroxide come in several physical forms such as flakes, pellets and liquid solutions, and each form is suited to different industrial applications. Specifically:
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NaOH: Flake caustic soda is the most common type on the market due to its ease of transportation and storage. Pellet NaOH dissolves quickly and is often preferred in soap production and high-grade detergents. Liquid NaOH is widely used in water treatment, system cleaning and as a raw material for many chemical manufacturing processes.
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KOH: KOH solution is used in liquid fertilizers, cosmetics and biodiesel. Flake KOH is applied in battery manufacturing, pharmaceuticals and cosmetics. Pellet KOH is less common and is typically used in industries that require rapid dissolution.
How to distinguish NaOH and KOH in practice
Distinguishing NaOH from KOH by visual inspection alone is not easy because both are white solid flakes or pellets, highly hygroscopic, and strongly alkaline. However, during purchasing and usage, you can still identify them through the following characteristics.
1. Observe appearance and hygroscopic level
Both NaOH and KOH absorb moisture, but KOH is significantly more hygroscopic. KOH flakes/pellets soften and liquefy quickly when exposed to air, and their surface often becomes slightly “wet” after a few minutes. Meanwhile, NaOH flakes absorb moisture more slowly and remain dry and solid for longer after opening the package.
This is not an absolutely accurate method, but it is very useful for preliminary inspection when receiving materials.
2. Heat release when dissolving (exothermic intensity)
When dissolved in water, both NaOH and KOH release strong heat. However, the “hotness” users feel depends on how they compare them. In practice, with the same mass (kg), NaOH feels slightly more exothermic than KOH. This is because NaOH has a lower molar mass, so 1 kg contains more reacting particles.
3. Color and clarity of the solution
When dissolved, KOH solutions tend to be clearer and rarely contain residues if the product is high quality. In contrast, liquid caustic soda may sometimes leave small residues or appear slightly cloudy if purity is lower. However, this depends on product quality, so it should only be used as a supporting factor.
4. Check packaging, labeling, and relevant certificates
This is the most important method in chemical commerce. KOH packaging usually states Potassium Hydroxide, Caustic Potash, with common purities: 85%, 90%, 95%. NaOH packaging states Sodium Hydroxide, Caustic Soda, typically 98–99%.
A reliable Certificate of Analysis (COA) will show indicators such as KOH/NaOH content, K⁺/Na⁺ levels, carbonate content, moisture, etc., which help detect adulteration.
5. Qualitative tests in laboratory
This is the most accurate and safest method when performed correctly. These methods are typically used in quality control labs of importers or large distributors.
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Metal ion analysis (K⁺ and Na⁺) using AAS, ICP-OES, or emission spectroscopy gives the clearest results.
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Acid–base titration determines actual concentration to detect dilution or mixing.
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When burned, Na⁺ produces a yellow flame, while K⁺ produces a pale purple flame.
Conclusion
NaOH and KOH are both important strong bases in industry, but each possesses its own chemical properties and application advantages. Understanding their differences helps businesses optimize costs, choose the correct chemical, and ensure safety and efficiency in production processes.
Although there are many ways to distinguish them, the practice of mixing NaOH into KOH still exists and can happen when suppliers lack integrity. Because both are strong bases, look similar in appearance, and NaOH is significantly cheaper, buyers may find it difficult to detect adulteration immediately.
Therefore, choosing a reliable supplier and conducting periodic testing are essential to avoid risks. You can place complete trust in KPTCHEM, as we specialize in supplying chemicals to both domestic and international markets. Our high-purity chemical products, including NaOH and KOH, are guaranteed in quality and come with full and clear COA and MSDS documentation.
