Which Addition to Hard Water would Reduce its Conductivity, Washing Soda or Rain Water? (page 3)

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Author: Michael Calhoun

Terms, Concepts and Questions to Start Background Research

Hard water, soft water, electrical conductivity, electrolytes, calcium ion, magnesium ion, metal electrodes, Washing soda, sodium carbonate, and ions

Experimental Procedure

  • This project requires the use of hard water and should be conducted on a day where it is ether raining or it is forecast to rain.
  • The young investigator can perform a simple unscientific test for hard water by opening the water faucet and filling up a bottle having a cap with about a half-cup of water; add ten drops of dish washing detergent and shake well. If a soapy suds solution foams up quickly the water is not hard.
  • If suds do not foam up but instead a milk-curd-like or soapy film forms instead then the water is likely hard and can therefore be used in this project.
  • If hard water is present place equal amounts of hard water into two cups, and the same amount of distilled water into a third cup.
  • Straightened 6 paper clips and using tape fasten the clips to opposite sides of each of the three cups.
  • Measure the conductivity of the distilled water and the hard water. Do not place the alligator clips directly into the water. This will result in the eventual corrosion of the clips. Instead, clamp the alligator clips to the paper clips that have already been placed in the waters as shown to the left. 
  • Depending of the conductivity device being used record whether or not the LED glows.
  • Place a  in the table that corresponds to the light produced by the LED. Based on the brightness of the LED classify the waters as “good,” “moderate,” “weak,” or “not a conductor”
Untreated Samples

             LED Light Intensity & Conductivity Classification

 Moderately Bright 
   No Light
Distilled Water
Hard Water
  • Collect rain water in a separate clean cup. Dilute one of the hard water samples with the rain water by half. Stir the mixture. Next add a small tablespoon of washing soda to the 2nd hard water sample and stir. Use separate spoons for each action. Nothing should be added to the cup with distilled water. This cup will serve as a control. 
  • Allow the samples to sit undisturbed for about halve an hour then measure the conductivity of the two samples following the same procedure as before. Record the results in the data table.
  • Place a  in the table that corresponds to the light produced by the LED. Based on the brightness of the LED classify the waters as “good,” “moderate,” “weak,” or “not a conductor”
Treated Samples

          LED Light Intensity & Conductivity Classification

 Moderately Bright
     No Light

Rain water Dilution

Washing Soda Addition
  • Using graph paper or a computer equipped with Excel® visually display the data in the table by plotting a bar graph similar to the one shown of the treated hard water vs. conductivity.


Title: Calcium and Magnesium in Drinking Water, Author and Publisher: World Health Organization, ISBN-13: 9789241563550 and ISBN: 9241563559 

This book addresses the question can calcium and magnesium (“hardness”) in drinking water contributes to preventing disease. There is chapter that discusses how climate change will increase the use of high tech treatments for hard water. This book can be consulted the young investigator and his or her parents (teachers) for general information about calcium and magnesium the main constituents of hard water.

Note: The Internet is dynamic; websites cited are subject to change without warning or notice!

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