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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Kelwin Joanes –                 

Teacher – Minati Sahu

Chemistry – Suitability of Pool Water

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  and destroying the enzymes and structures inside the , rendering them oxidized and harmless.  

The levels of HOCl and OCl- vary with the pool's . If the pH is too high, not enough HOCl is present and pool cleaning can take much longer than normal. Ideally, the level of pH in the pool should be between 7 and 8; 7.4 is ideal -- this is the pH of human tears.

While the bacteria-killing properties of chlorine are very useful, chlorine also has some side effects that can be annoying to humans, and possibly even hazardous. Chlorine has a very distinctive smell that most find unpleasant, and some find overwhelming. There is also the "itch factor" – chlorine can cause certain skin types to become itchy and irritated. The hypochlorite ion causes many fabrics to fade quickly when not rinsed off immediately after exiting the pool. This is why swimsuits look faded and worn so early in the summer. Extremely high amounts of chlorine gas hovering above the pool can be hazardous to human breathing.

Variables:

  • Independent Variable:

The volume of pool water used was varied so as to obtain more accurate readings.

  • Dependant Variable:

The dependent variable of this experiment was the volume of sodium thiosulphate used.  

  • Controlled Variables:

The concentration of sodium thiosulphate used was constant throughout the experiment by using the ; the number of drops of starch solution used was exactly 4 drops, and a constant amount of potassium iodide was ensured by using an electronic balance.

Materials and Method:

Apparatus:

  • A 100 cm3 burette
  • One 250 ml conical flask
  • 50 cm3 measuring cylinder
  • 250 ml beaker
  • Retort stand
  • 50 cm3 measuring cylinder
  • An electronic balance

Chemicals:

  • Swimming pool water
  • Starch Solution with dropper
  • Distilled water
  • Solid potassium Iodide – KI
  • Concentration of 0.025 mol dm-3 of sodium thiosulphate (Na2S2O3)
  • Aqueous silver nitrate (AgNO3)
  • Universal indicator solution and colour chart
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Method:

  1. First we divided ourselves into groups of about three. Then we made a solution of sodium thiosulphate of 0.025 mol dm-3. This solution was then left for about one day before we began the experiment.
  2. On the day of the experiment, we began testing the pool water, by first checking its pH level. This was done by putting a little of it in a test tube and adding a few drops of universal indicator solution and comparing the colour change with those colours (with corresponding pH on the colour chart.
  3. Then we tested the ...

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