Bleaches were the focus for the 2019 O level Chemistry Paper 2 Database question.
Bleach is a necessity that is used daily, to remove colour pigmentations and to sterilise unhygienic areas. It is used to whiten wood pulp to make tissue papers or the paper we use to write on, and in flour for making bread.
Bleaching works by releasing oxygen molecules in a process (oxidation). The released oxygen molecules break up the chemical bonds of chromophores and reflect either no colour or a colour outside of the visible spectrum. The active ingredient in Clorox household bleach is sodium hypochlorite (NaOCl), which performs the bleaching, stain removal and disinfecting functions. Other chemical ingredients in Clorox include sodium chloride (salt), which thickens and stabilizes the solution.
Although household bleach is not corrosive or toxic, bleach exposure can cause irritation in the eyes, mouth, lungs and skin. Not only is bleach harmful on its own, but its interactions with other commonly used chemicals can produce harmful reactions. When bleach comes in contact with ammonia, it can react to form chlorine gas, which causes cellular damage in the nasal passageways and lungs. The accidental mixture of these two products in homes has resulted in death.
In addition, chlorine gas can also form when bleach NaOCl reacts with acids, such as vinegar. Bleach is especially damaging to the environment because it lingers for many years. Even small amounts of the toxic chemical can accumulate in air and water over time, which can eventually result in adverse health effects. In the O level Chemistry Paper, besides NaOCl, another bleach of consideration was hydrogen peroxide.
