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Testing the Suitability of Pool Water. The expected amount of chlorine which is considered safe and could be found in the swimming pool water should be between 3 and 5 mg/dm3

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Experiment - Suitability of Pool Water Introduction: Aim: To design an experiment to test the suitability of pool water for usage. Hypothesis: The expected amount of chlorine which is considered safe and could be found in the swimming pool water should be between 3 and 5 mg/dm3 General Background: Chlorine was first discovered in the eighteenth century by Swedish Chemist Carl Scheele, and is today one of the most produced chemicals with a variety of uses. One of its major applications is in the purification and disinfection of water. There are usually millions to billions of microorganisms present in the water and so a disinfectant must be added kill the pathogenic micro-organisms. The disinfectants used for swimming pool water disinfection must meet certain criteria. They should be harmless and non-irritating to swimmers and attendants as well as being active in small concentrations. Chlorine - based disinfectants are among the most frequently used chemicals in the disinfection and maintenance of swimming pool water. They kill bacteria through a fairly simple chemical reaction. The chlorine solution poured into the water breaks down into many different chemicals, including hypochlorous acid (HOCl) and hypochlorite ion (OCl-). Both kill microorganisms and bacteria by attacking the lipids in the cell walls and destroying the enzymes and structures inside the cell, rendering them oxidized and harmless. ...read more.


cm3 Average Volume of Na2S2O3 (� 0.10) cm3 1 50 0 1.5 1.5 1.6 2 0 1.7 1.7 3 100 0 3.1 3.1 3.15 4 0 3.2 3.2 5 150 0 4.8 4.8 4.75 6 0 4.7 4.7 1) Amount of Chlorine for 50cm3 of Pool water: * Volume of pool water = 50 � 0.5 cm3 = 0.05 � 0.0005 dm3 * Average Volume of Na2S2O3 = 1.6 � 0.1 cm3 = 0.0016 � 0.0001 dm3 * Concentration of Na2S2O3 = 0.01 M * No. of moles of Na2S2O3 = Concentration (mol dm-3) � Volume (dm3) = 0.01 mol/dm3 � [0.0016 � 0.0001] dm3 = 0.000016 � 0.000001 mole Chemical Equations: * 2KI (s) + Cl2 (aq) ==> 2KCl + I2(aq) * 2Na2S2O3 (aq) + I2 (aq) ==> 2NaI (aq) + Na2S4O6 (aq) But the molar ratio between sodium thiosulphate and Iodine is 2:1 Therefore, * No. of moles of Iodine = No. of moles of sodium thiosulphate (Na2S2O3) 2 = (0.000016 � 0.000001) 2 * No. of moles of Iodine = 0.000008 � 0.0000005 mole But the molar ratio between iodine and chlorine is 1:1 Therefore, * No. of moles of Chlorine = No. of moles of Iodine = 0.000008 � 0.0000005 mole Given Mass = No. ...read more.


* A white tile should be used to clearly see the colour change, which can then be compared with other colours on the colour chart. * The error due to the limitation of the burette can be reduced by doing even more titration repetitions, like eight or ten of them. Improvements: * The volume readings all had a high uncertainty of 0.5 cm3. This was due to the usage of a measuring cylinder to measure the volume. More accurate readings of the volume could have been obtained by using a pipette instead of a measuring cylinder. * Universal indicator solution was used to find the pH by comparing the colour change with colours on a pH colour chart. Through this method it was difficult to determine the exact value of the pH, as the colour chart didn't contain all possible colour changes with corresponding value of pH. A digital pH meter should have been used to measure the pH of the pool water, instead of using universal indicator solution. This would provide dot accurate readings for the pH. Further Research: * Some further investigation could be done on the amounts of other chemicals present in pool water, their applications and effects (if any). And also there could be an investigation on the chlorine content in drinking water and tap water, so as to test its suitability for drinking, bathing, and washing of clothes. ...read more.

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