A bleach is a chemical that removes colour or whitens. Common chemical bleaches include household “chlorine bleach” approximately 6% sodium hypochlorite (NaClO), and “oxygen bleach,” which contains hydrogen peroxide or a peroxide-releasing compound such as sodium perborate or sodium percarbonate. To bleach something is to apply bleach, sometimes as a preliminary step in the process of dyeing. Bleaching powder is calcium hypochlorite.

Since bleaches are strong oxidizing agents, they can be quite hazardous, especially when reacted with other common household chemicals.

Mixing sodium hypochlorite with acids like vinegar or drain cleaners containing sodium bisulfate (sodium hydrogen sulfate), or even lemon juice can release chlorine. Hypochlorite and chlorine are in equilibrium in water, the position of the equilibrium is pH dependant and low pH (acidic) favors chlorine, Cl2 + H2O H+ + Cl- + HClO.

Chlorine is a respiratory irritant that attacks mucous membranes and burns the skin. You can smell as little as 3.5 parts per million (ppm). 1000 ppm is likely to be fatal after a few deep breaths. Sodium hypochlorite and ammonia react to form a number of products, depending on the temperature, concentration, and how they are mixed. The main reaction is chlorination of ammonia, first giving chloramine (NH2Cl), then NHCl2 and finally nitrogen trichloride (NCl3). These materials are very irritating to eyes and lungs and are toxic above certain concentrations.

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