General Chemistry 101/102 Laboratory Manual University of North Carolina at Wilmington

Water Hardness: Determination with EDTA
• Purpose
• To determine the “hardness” of a water sample using an EDTA titration.
 To learn and practice quantitative techniques for determining the concentrations of solutionTo determine the “hardness” of a water sample using an EDTA titration.
 Safety Considerations
 Keep the pH 10 buffer in the hood. Avoid breathing ammonia vapors from the buffer.
 Eriochrome Black T will stain skin and clothes.
 All waste materials can be safely rinsed down the sink.
 Water Hardness: Determination with EDTA
 Water is said to be “hard” when it contains Ca2+ and Mg2+ ions. These ions react with soap to form an insoluble substance called “soap scum”.
Ca2+ and Mg2+ ions along with other metal ions such as Fe3+ and Pb2+ can be removed from hard water by the addition of EDTA (ethylenediaminetetraacetic acid)
 EDTA has a greater affinity for Ca2+ and Mg2+ when it is in the form of the dihydrogen anion H2EDTA2-. This is the ionic form of EDTA at pH 10.