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EDTA Titration Lab Prep

EDTA Titration Lab Prep. EDTA and Water Hardness Titration. Water hardness is dissolved minerals Ca 2+ + Mg 2+ Titrate dissolved Ca 2+ and Mg 2+ with EDTA (Na 2 H 2 Y) Ca 2+ + H 2 Y 2   CaY 2  + 2H + Use metallochromic indicator for endpoint MgIn  + HY 3  HIn 2  + MgY 2

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EDTA Titration Lab Prep

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  1. EDTA Titration Lab Prep

  2. EDTA and Water Hardness Titration • Water hardness is dissolved minerals • Ca2+ + Mg2+ • Titrate dissolved Ca2+ and Mg2+ with EDTA (Na2H2Y) • Ca2+ + H2Y2 CaY2 + 2H+ • Use metallochromic indicator for endpoint MgIn + HY3 HIn2 + MgY2 • Calculations • Reaction stoichiometry nCa = nY = MYmLY • Report hardness as ppm CaCO3 (mg CaCO3/L)

  3. Spectrophotometric Endpoint Alternative to visual endpoint detection

  4. Absorption Spectra of Calmagite End point reaction MgIn + HY3 HIn2 + MgY2 MgIn Red form HIn2 Blue form Monitor absorbance at wavelength with maximum change in absorbance.

  5. 42.55 mL Titration of Mg2+ (or Ca2+) with EDTA Mg2+ + HY3 MgY2 + H+

  6. Ocean Optics Spectrometer with Fiber Optic Probe From light source To spectrometer Lens Analyte solution Mirror

  7. Summary • Water hardness titration determines dissolved Ca2+ and Mg2+ salts. • EDTA forms a 1:1 complex with Ca2+ or Mg2+ • Endpoint detection methods • Visual • Spectrophotometric • Report water hardness as ppm CaCO3

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