Sodium hypochlorite (also known as bleach), with the chemical formula NaClO, is an inorganic chlorine-containing disinfectant. Solid sodium hypochlorite is a white powder, and general industrial products are colorless or light yellow liquids with a pungent odor.

Preparation of sodium hypochlorite

Chlorine gas dissolves in cold and dilute sodium hydroxide solution to produce sodium hypochlorite, sodium chloride and water:

Cl₂+ 2NaOH= NaClO + NaCl + H₂O

Note that chlorine gas dissolves in hot (generally considered to be around 60 degrees Celsius) and concentrated sodium hydroxide solution will not produce sodium hypochlorite, but will produce sodium chloride, sodium chlorate and water:

3Cl₂ + 6NaOH= 5NaCl + NaClO₃ +3H₂O

Generally speaking, if the temperature of the sodium hydroxide solution is relatively high but has not reached 60 degrees Celsius, the total reaction equation will be the result of the indefinite addition of the above two equations. The higher the temperature, the greater the proportion of the second equation, and vice versa.

Advantages of sodium hypochlorite disinfection

As a truly efficient, broad-spectrum, safe and powerful sterilizing and antiviral agent, it has a good affinity with water and can be miscible with water in any ratio. It does not have the safety hazards of liquid chlorine, chlorine dioxide and other agents, and its disinfection and sterilization effect is recognized to be equivalent to chlorine. It is precisely because of this feature that it has a good disinfection effect, accurate addition, safe operation, convenient use, easy storage, no toxicity to the environment, no gas leakage, and can be added in any environmental working conditions.

The principle of sodium hypochlorite disinfection

The main mode of action of sodium hypochlorite in disinfection and sterilization is to form hypochlorous acid through its hydrolysis, which further decomposes to form new ecological oxygen [O]. The strong oxidizing property of new ecological oxygen denatures the proteins of bacteria and viruses, thereby killing pathogenic microorganisms. According to chemical determination, the hydrolysis of sodium hypochlorite is affected by the pH value. When the pH exceeds 9.5, it will be unfavorable for the generation of hypochlorous acid. For sodium hypochlorite with a concentration of ppm, it is almost completely hydrolyzed into hypochlorous acid in water, and its efficiency is higher than 99.99%. The process can be simply expressed by the chemical equation as follows:

NaClO + H2O ＝ HClO + NaOH

HClO → HCl + [O]

Secondly, in the process of sterilization and killing viruses, hypochlorous acid can not only act on cell walls and virus shells, but also because hypochlorous acid molecules are small and uncharged, they can penetrate into bacteria (viruses) and undergo oxidation reactions with bacterial (viral) proteins, nucleic acids, and enzymes, or destroy their phosphate dehydrogenases, causing sugar metabolism disorders and leading to cell death, thereby killing pathogenic microorganisms.

R-NH-R + HClO → R2NCl+ H2O 

(Bacterial Protein)

The higher the concentration of sodium hypochlorite, the stronger the bactericidal effect. At the same time, the chloride ions produced by hypochlorous acid can also significantly change the osmotic pressure of bacteria and virions, causing their cells to lose th