Guidelines For Classification Of Water Hardness

1175 Words Nov 8th, 2015 5 Pages
Water is measured in milligrams per liter or parts per million. In Table 1, the guidelines for classification of water hardness can be found. This table shows the different amounts of CaCO3, calcium carbonate, in mg/L that cause water to be soft too hard.

Hardness in mg/L CaCO3 Degree of Hardness
0 – 30 Very soft
31 – 60 Soft
61 – 120 Moderately soft/ moderately hard
121 – 180 Hard
>180 Very hard Table 1.4 General guidelines for classification of water hardness

Two methods that are utilized in measuring the hardness of water are EDTA and AA. The EDTA, ethylene diamine tetraacetic acid, method contains 3 steps. First, preparation of a standard Ca2+ solution is needed. Second, standardization of EDTA with a standard calcium solution has to occur. The final step is an analysis of an unknown Ca2+ sample with the standardized EDTA solution (Community College of Rhode Island). During the lab, a NH3/NH4 buffer was added to the sample water to make the solution basic, a pH of around 10. EBT, eriochrome black T, was then added to this solution. The solution turned blue when EBT was added. If magnesium were present in the water, the solution would turn red. Then, EDTA, which has a known concentration, was added the red solution. The EDTA reacts with the calcium that is present in the solution bringing the solution back to its clear color. After it reacted with calcium, it will react with the magnesium turning the solution to blue. Overall, magnesium has to be…

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