1、 The physical and chemical properties of the two are different:
1. Potassium hydroxide is white orthorhombic crystal, and industrial products are white or light gray block and rod. The relative density is 2.044 (20 ℃). Melting point 360.4 ℃. Boiling point 1320 ~ 1324 ℃. It is easily soluble in water. It emits a large amount of dissolution heat when dissolving. It has strong water absorption. It can absorb water and dissolve in the air, absorb carbon dioxide and gradually turn into potassium carbonate. Soluble in ethanol, slightly soluble in ether. It is highly alkaline and corrosive, and its properties are similar to caustic soda.
2. Sodium hydroxide is a colorless transparent crystal with a relative density of 2.130. Melting point 318.4 ℃. Boiling point 1390 ℃. There are two kinds of sodium hydroxide: solid and liquid. In the pure solid state, the appearance is white (block, flake, rod and granular) and brittle; In the pure liquid state, the appearance is colorless and transparent liquid. Sodium hydroxide dissolved in water will completely decompose into sodium ions and hydroxyl ions, so it has strong alkalinity. It is easy to deteriorate into sodium carbonate in air; Reaction with aluminum can produce hydrogen. In 1986, a British oil tank truck mistakenly loaded an aqueous sodium hydroxide solution with a weight percentage concentration of 25%. The sodium hydroxide changed chemically with the aluminum on the oil tank wall, resulting in permanent damage to the oil tank due to internal pressure overload.
2、 Potassium hydroxide and sodium hydroxide can be used interchangeably in chemical analysis. However, in some applications, the two cannot be used interchangeably. For example, potassium hydroxide is specified for hydrogen generator; Sodium lime for medical use, sodium hydroxide is specified. Sodium hydroxide is more hygroscopic than potassium hydroxide, so potassium hydroxide is often used in chemical analysis; If used as a desiccant, use sodium hydroxide.
3、 Both of them are highly corrosive, can not contact with metal containers, and are easy to deliquescence, so they should be sealed and stored.
4、 In saponification reaction, potassium oxide makes weak soap, while sodium hydroxide makes hard soap.
5、 The market price of potassium hydroxide is much higher than that of sodium hydroxide.
6、 Application differences between the two:
1. Potassium hydroxide is used as analytical reagent, saponification reagent, desiccant and water absorbent; Used for preparing oxalic acid and various potassium salts; Electroplating, engraving, lithography, etc; It is also used in printing and dyeing, bleaching and mercerization, and is widely used as the main raw material for the manufacture of man-made fibers and polyester fibers, as well as melamine dyes.
2. Sodium hydroxide is used in the production of paper, soap, dyes, rayon, metal smelting, petroleum refining, cotton fabric finishing, coal tar product purification, food processing, wood processing and machinery industry.