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Defines pH indicators and explains how they function.

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Clean and Sparkling

Clean and Sparkling

Credit: William Warby
Source: http://www.flickr.com/photos/26782864@N00/8189925965
License: CC BY-NC 3.0

There is nothing more relaxing than a dip in a pool on a hot day. If you go to a public pool, you simply enjoy the water and don’t worry about how the pool is maintained. If you own a pool, on the other hand, you can be kept very busy keeping the water clean and properly balanced to avoid skin irritations and kill all the microorganisms that may have taken up residence.

News You Can Use

  • An important part of maintaining clean water is testing water quality. Several common tests include chlorine (or bromine) level for disinfecting the pool, pH to maintain a slightly basic water to avoid irritating the skin (and help in killing the bacteria, and total alkalinity, calcium hardness, and total dissolved solids to cut down on scale build-up and other deposits.
  • For testing, you can either use test strips or test chemicals. The test strip is simply immersed in the water for a moment, then allowed to react. Color changes on the strip relate to the amounts of the different components needed for maintenance of clean and safe water. Alternatively, a plastic tester can be used. This device scoops up water from the pool (immerse the device about eighteen inches below the surface for best sampling.) Then different test reagents are added to the water in each chamber. Color reactions can be compared to a chart that will tell you the status of each parameter and how to correct any imbalances.
  • Credit: Bill Jacobus
    Source: http://www.flickr.com/photos/billjacobus1/192325060/
    License: CC BY-NC 3.0

    Modern pools may employ chlorine generators to maintain the quality of pool water [Figure2]

  • The pH is measured with an indicator that turns color depending on the acid content of the water. Usually a slightly basic pH is desired (~7.4), so a good indicator is one that has a discernible color change in that region. Total alkalinity is an index of the buffering capacity of the water – how hard it is to change the pH. Chlorine measurement also involves a color reaction. Depending on the testing material used, you can measure free, combine, or total chlorine. Only the free chlorine is effective in killing bacteria.
  • Watch a video at the link below that describes bromthymol blue as an indicator:


Show What You Know

Use the links below to learn more about pool testing. Then answer the following questions.

  1. How is chlorine maintained in a pool?
  2. What is a desirable pH range?
  3. Are test strips as accurate as wet chemistry kits?
  4. How is titration involved in water testing?
  5. What is one important step to take in using test strips?

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Image Attributions

  1. [1]^ Credit: William Warby; Source: http://www.flickr.com/photos/26782864@N00/8189925965; License: CC BY-NC 3.0
  2. [2]^ Credit: Bill Jacobus; Source: http://www.flickr.com/photos/billjacobus1/192325060/; License: CC BY-NC 3.0

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