Naturally obtained water consists of bacteria, or pathogens. When consumed, these pathogens have been known to cause disease, and thus water consumed/used must be treated to kill the pathogens. “Chlorine is primarily adapted to destroy or to deactivate disease-producing microorganisms in public water supplies…” (n.d, 2003, page 2). It is added to water in gaseous form, or has sodium/calcium hypochlorite. The total chlorine is the amount of chlorine that reacts with the substances (pathogens and metals) present in the water, and the remainder of chlorine which is left un-reacted with the chlorine (in excess) is known as the residual. The chlorine residual is normally ingested by humans as it is a very small content, however, an excess of chlorine residual can have detrimental effects when consumed in water, including “potentially carcinogenic compounds such as chloroform…” (n.d, 2003, page 3). Therefore, it is very important to test the water and the residual chlorine content that it may have before it is diverted into the public water supply due to the harmful health effects it may have on those who consume it.
The residual Chlorine content can be tested by titrating the various types of water containing potassium iodide with Sodium Thiosulphate (Neuss, n.d.). The chlorine content is calculated by using the following Reduction and Oxidation equations (of the entire process):
(Addition of Potassium Iodide to the water).
2KI(aq) + Cl2(aq) 2KCl(aq) + I2(aq)
(Titrating the water containing potassium iodide with Sodium Thiosulphate)
I2(aq) + 2Na2S2O3(aq) 2NaI(aq) + Na2S4O6(aq)
As a result, this experiment is also of great importance to me as it is going to allow me to test the chlorine content in the water that I may be consuming through drinking or washing, and therefore excess chlorine content can have a very harmful health impact.
How does the residual chlorine content vary...