Hardness Of Water Essay

3577 Words 15 Pages
James Apostolico
November 6, 2014
The Chemistry of Natural Waters
Chemistry 111
Section: 005
Kareem Ali, Dima Alfawaz
Stephanie Le Clair

Introduction Water hardness is a way of defining the quality of water based upon the amount of Ca2+ and Mg2+ions that the sample contains.1 Water mostly becomes hard by flowing over weathering rocks which release these ions into the water. These released ions dissolve in water and then react with various elements, ions and compounds that come into contact with the water, which in some cases can become a nuisance.
When trying to wash your hands or dishes, calcium reacts with soap to form soap scum. This soap scum leaves hard water spots on dishes and leaves an uncomfortable film on your
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The true concentration of hardness of the tap water sample in molarity is
3.0 X 10-3 M. The following table lists all of the molarities for each sample when it’s untreated, treated with baking soda soap and ion-exchange resin.
Table 6: EDTA Molarities of Water Samples
Sample Untreated (M) Baking Soda Soap (M) Ion-Exchange Resin (M)
Aquafina Bottled Water6 2.00 X 10-4 < 2.00 X 10-4 < 2.00 X 10-4
Shulze Hall Tap Water7 3.00 X 10-3 2.00 X 10-3 1.20 X 10-3
Pond Water from Hammond Park8 4.40 X 10-3 4.00 X 10-3 2.00 X 10-3

To find the ppm of CaCO3 you must first convert the molarity to mg/L. The density of the solution is close to 1 g/mL because it’s a dilute aqueous solution, so ppm is equal to mg/L.3 The ppm of the Shulze Hall tap water can be calculated by converting Molarity to moles per liter grams per L to mg per liter like so:

The following table contains the concentration of water hardness, CaCO3, in ppm for all three water samples when they’re untreated, treated with baking soda soap and ion-exchange resin.
Table 7: CaCO3 Concentration of Water Samples
Sample Untreated (ppm) Baking Soda Soap (ppm) Ion-Exchange Resin (ppm)
Aquafina Bottled Water6 20.0 <20.0 <20.0
Shulze Hall Tap Water7 300 200
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The data from each are very close to one another. In the analysis of the pond water, the EDTA value was greater by 8 ppm. In the analysis of the tap water, the AA value was greater by 28 ppm, (this was the largest difference). In the analysis of the Aquafina water, the EDTA value was greater by 16.15 ppm. The EDTA value should be greater because it measures all polyvalent ions and not just the calcium and magnesium like the AA method measured. EDTA cannot distinguish between different polyvalent ions though. There are a few areas that can cause very serious error in this experiment. The largest error occurs during titration. The number of drops of EDTA can be easily skewed. As outlined in Q6 in my lab notebook7, the error of one drop is 40 ppm. This is an incredibly large range of error considering water hardness is measured in ranges of 60 ppm10. This outlines the imprecision in the results. The accuracy of EDTA can also get skewed if off by a single drop. In section C in my lab notebook7, it is shown that the percent error in one drop is 20% which is very

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