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

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

7. Data File. Absorbance vs Volume EDTAmL

8. End Point Determination
Equivalence point occurs at intersection of the two straight lines
1. Graphical measurement
2. Algebraic approach.
Set rhs of two equations equal, solve for x (where x = volume at equivalence point).

9. 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