Hypochlorous acid is a weak acid that can only exist in solution, because it is highly unstable when isolated in a pure form. There are a number of uses for this chemical, most of which take advantage of its strong oxidizing properties, which allow it to be used in bleach and disinfectant, among many other things. Many manufacturers produce this acid for sale to both industrial users and ordinary consumers, and many stores carry it, typically in the household cleaning section. Though it can be safely used when diluted, it can be very dangerous when concentrated.
The chemical formula for this compound is HClO. It is classically obtained by dissolving chlorine in water, although it can also be obtained by reacting chlorine with mercury(II) oxide to create a pure form, which is greenish-yellow in color. The "chlorine bleach" sold for disinfectant and laundering contains hypochlorous acid, and the systems used to chlorinate many water supplies rely on it to kill unwanted microorganisms in the water, with the acid creating conditions that make life unsustainable for these microbial invaders.
While this compound can be very useful in many applications, including household laundry, cleaning, and sterilization of clinical environments, it can also be dangerous in certain settings. It can also cause skin irritation and damage to the eyes, and people should use caution or wear protection when working with it to avoid splashbacks.
In bleaching, the acid acts to oxidize the agents that cause stains. This strong oxidizing power can also make the chemical very dangerous, because it can become explosive in certain settings. Adding acids to a solution that contains it will precipitate this process, making the mixture unstable, releasing chlorine gas, and potentially causing an explosive chemical reaction.
In disinfecting, a solution with a pH balance of around five to six is usually optimal. The compound needs to be handled carefully because it can release dangerous chlorine gas if it is mixed with the wrong chemicals. Chlorine gas can cause considerable health problems or death, especially in a space that is poorly ventilated, which is one reason why it is inadvisable to mix household chemicals at random.
Hypochlorous acid should be stored in a sealed container in a cool dry place out of the reach of children and pets. It is a good idea to mark the container to make sure that people are aware of the contents, and to add a warning that it should not be used with acids.