Swimming pool chemistry

Tie presence of disease-causing bacteria in swimming pools is a major health concern. 

Chlorine gas is added to the water in some large commercial swimming pools to kill bacteria. However, in most home swimming pools, either solid calcium hypochlorite (Ca(OCl)2) or an aqueous solution of sodium hypochlorite (NaOCl) is used to treat the water. Both compounds dissociate in water to form the weak acid hypochlorous acid (HOC1). Hypochlorous acid is a highly effective bactericide. By contrast, the hypochlorite ion (OC1-) is not a very effective bactericide. Use the information above to answer the following questions about the acid-base reactions that take place in swimming pools. 

Write an equation that shows the reaction between hypochlorous acid and water. Identify the acid, base, conjugate acid, and conjugate base in this reaction. 

What effect does the addition of hypochlorite ion have on the pH of swimming pool water  

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Swimming pool chemistry is fairly convoluted and we will be probing more as we go along. But before going off the deep end, we will consider pH here and how it affects swimming pool chemistry. 

Contamination of silicon wafers by heavy metals is a major cause of low yields in the manufacture of electronic devices. Concentrations in the order of 1011 cm-3 [Ha2] are sufficient to affect the device performance, because impurity atoms constitute recombination centers for minority carriers and thereby reduce their lifetime [Scl7]. In addition, precipitates caused by contaminants may affect gate oxide quality. Note that a contamination of 1011 cnT3 corresponds to a pinhead of iron (1 mm3) dissolved in a swimming pool of silicon (850 m3). Such minute contamination levels are far below the detection limit of the standard analytical techniques used in chemistry. The best way to detect such traces of contaminants is to measure the induced change in electronic properties itself, such as the oxide defect density or the minority carrier lifetime, respectively diffusion length. 

Copaken J. 1990. Trihalomethanes Is swimming pool water hazardous. In Water chlorination Chemistry, Environmental Impact and Health Effects, volume 6. Chelsea, MI Lewis Publishers, Inc. 

Surely, many such common reactions could be utilized for the intentional destruction of unwanted herbicides and their residues (41). Metham might be caused to react simply with aqueous ammonia to form harmless methylthiourea many herbicides including prometryne and metribuzin (Sencor) might be degraded by dilute hypochlorite ("chlorinated lime") of the type used to purify swimming pools, and the photodecomposition of others (such as 2,4,5-T) might be accelerated by cheap nontoxic photosensitizers such as acetone (Table III) (42). The variations of environmental chemistry applications to control and direct herbicide persistence and effectiveness now appear endless. 

As pervasive as redox reactions are, however, they are certainly not all there is to chemistry. Another very common and important type of reaction is found in the acid-base reactions that occur in the air, on skin, in stomachs, in sewers, and even in swimming pools and fish tanks. The fish-tank indicator that we used to detect carbon dioxide is an acid-base indicator. It worked to detect carbon dioxide because carbon dioxide dissolved in water turns water slightly acidic. Intrigued Read on. 

These considerations are important because they show that the form in which chlorine is added can affect the water chemistry in different ways. The addition of significant amounts of Cl2(g) to a low alkalinity water could depress pH to an unacceptably low value. Bleach addition would not cause such a pH depression. The use of HTH as a disinfectant in swimming pools is not to be recommended because the increase in hardness and alkalinity that accompanies its addition can aggravate scale (CaCOa precipitation) problems. 

Unhoch, M. J. and Roy, D. V., 1997. The Use of PHMB as a Swimming Pool and Spa Sanitizer. Proceedings of the 3rd Annual Water Chemistry Technical Seminar, December 12, 1997, Los Angeles. J. Swimming Pool and Spa Industry. 

Vote, R. D. and Michael, J. U., 1996. The Use of PHMB as a Sanitizer in Domestic Spas, In Water Chemistry and Disinfection- Swimming Pools Spas. Proceedings of the 1st Annual Chemistry Symposium of the National Spa and Pool Institute. 1996. NSPI, Arlington, VA pp. 98-103. 

Dry chemistry systems are very widely used in physician s offices, hospital laboratories and many homes worldwide. They are used for routine urinalysis, blood chemistry determinations, immunolomcal and microbiolo cal testing. Today dry chemistry systems are also used mr assays in applications ranging from chlorine in swimming pools to coolant levds in cars and trucks 12). 

I don t know how ordinary people, lacking an engineering background, take care of their swimming pools. Unless you have lots of time, money, and a degree in water chemistry, do not buy a home with a pool. 

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