AP Chemistry Kits: Water Hardness, Students test for water hardness, Each

Details

Tap water contains various amounts of ions such as calcium, iron, magnesium, etc. The higher the concentration, the “harder” the water is; hard water is characterized by the inability of soap to form lather and the formation of “scum” in sinks and bathtubs.A sample of tap water is treated with EBT indicator. If the indicator turns from blue to pink, metal ions such as calcium and magnesium are present. To determine the concentration of ions present, the sample is titrated with a known molar concentration of EDTA.