Hypochlorous acid, an oxo acid of chlorine element, chemical formula is HClO, structural formula HO-Cl, wherein the valence of chlorine element is +1, which is the lowest oxo acid of chlorine element, but its oxidizing property is lower than that of chlorine element. It is extremely strong in oxyacids and is the second most oxidizing acid among chlorine oxyacids. It only exists in solution, the concentrated solution is yellow, the dilute solution is colorless, has a very pungent, chlorine-like odor, and is extremely unstable. It is a very weak acid, weaker than carbonic acid, and comparable to hydrosulfuric acid. Hypochlorous acid also has a strong bleaching effect, and its salts can be used as bleaching agents and disinfectants.
physical properties
Substance class: inorganic acid
State at room temperature: exists only in aqueous solution. The aqueous solution can be concentrated to a density of 1.282 in a vacuum, that is, a concentration of 40.1%. It begins to decompose at zero degrees and explodes when heated to room temperature. It is a very strong oxidant.
Color: colorless to light yellow-green (yellow-green is due to dissolved chlorine gas 7HClO====HClO3+2Cl2↑+Cl2O↑+3H2O)
Odor: Has a pungent odor similar to chlorine gas
Solubility (volume ratio to water): 1:2
chemical properties
weak acid
Hypochlorous acid is a monobasic weak acid with an ionization constant of 3×10Ka at 25°C.
Strong oxidizing
Hypochlorous acid can redox substances (such as Na2SO3, FeCl2, KI, C7H7O4N (litmus), etc.), so that colored cloth strips, magenta fade, and can make litmus solution into a colorless liquid. Such as: Na2SO3 + HClO = Na2SO4 + HCl (strong oxidant makes weak oxidant, weak acid makes strong acid)
A neutral solution of hypochlorous acid is a stronger oxidant than chlorine at standard conditions:
2HClO+2 H+2 e⇌Cl2↑+2 H2O E=+1.63V
Note: Standard conditions refer to 0°C, standard atmospheric pressure instability
Hypochlorous acid is very unstable and exists only in aqueous solutions. Under the condition of light, it decomposes according to the formula: 2HClO=light=2HCl+O₂↑. It is generally used as a bleach, oxidant, deodorant and disinfectant. In aqueous solution, hypochlorous acid is partially ionized into hypochlorite ClO (also known as hypochlorite anion) and hydrogen ion H. Salts containing hypochlorite are called hypochlorites. One of the most widely known household hypochlorite disinfectants is sodium hypochlorite (NaClO). Therefore, hypochlorous acid has strong oxidizing and bleaching effects, and the main component of commonly used bleaching powder is calcium hypochlorite. When pure chlorine gas is passed into water, hypochlorous acid and hydrochloric acid are formed: Cl₂ + H₂O = reversible = HClO + HCl. Hypochlorous acid is also a weaker chloric acid, and hydrochloric acid has a lower pH and alkalinity than it. But it has strong oxidizing and bleaching effects. Its salts can be used as bleaching agents and disinfectants. The most important hypochlorite is calcium salt, which is bleaching powder (calcium hypochlorite and basic calcium chloride). mixture) active ingredient. Bleaching powder can be obtained by the reaction of chlorine and slaked lime:
2Ca(OH)₂+2Cl₂=Ca(ClO)₂+CaCl₂+H₂O xCaCl₂+yCa(OH)₂+nH2O==xCaCl₂yCa(OH)₂nH2O
The smell of chlorine in the place where the bleaching powder is placed is due to the release of dichlorine monoxide.
The reason why the concentrated hypochlorous acid solution is pale yellow is because it is unstable and decomposes spontaneously:
7HClO====HClO3+2Cl2↑+Cl2O↑+3H2O
The produced Cl2 dissolves in water in molecular form and is pale yellow.
There are 3 forms of decomposition of hypochlorous acid in solution, which are independent of each other, called parallel reactions, namely:
1.2HClO = light = 2HCl+O₂↑
2.2HClO=dehydrated substance=Cl₂O↑+H₂O
3.3HClO =△= 2HCl+HClO₃
Under the direct action of sunlight, it is decomposed according to the first form; in the presence of dehydrated substances (such as CaCl₂), it is decomposed according to the second form; when heated, it is particularly easy to decompose according to the third form. If chlorine is passed into the hot alkali solution, the product is chlorate instead of hypochlorite: 3Cl₂+6KOH=KClO₃+5KCl+3H₂O
Chlorine monoxide reacts with water to generate hypochlorous acid: H₂O+Cl₂O=2HClO
Chlorine gas reacts with water to generate hypochlorous acid and hydrochloric acid: H₂O+Cl₂=HCl+HClO
Chlorine gas is passed into the water mixed with calcium carbonate powder, and the hypochlorous acid is accumulated in the solution, and the dilute hypochlorous acid solution can be collected by distillation of the reaction mixture.
2H₂O+2Cl₂+CaCO₃=CaCl₂+H₂O+CO₂↑+2HClO
The hypochlorous acid water machine produced by qinhuang water produces hypochlorous acid disinfection water by electrolyzing salt water, which is efficient, safe and fast. It is widely used in various disinfection and sterilization in the field of life.