Chloride Methods q Gravimetric Chloride q Potentiometric titration

Chloride Methods q. Gravimetric Chloride q. Potentiometric titration q. Visual Indicators ØMohr Method ØFajans Method ØVolhard Method

In all of these methods the chloride sample is dissolved & reacted with silver nitrate -1 Cl + +1 Ag Ag. Cl

Gravimetric Chloride • Use a balance to measure mass of sample and Ag. Cl Precipitate • No endpoint detection

Potentiometric Titration • Balance for mass of sample • Buret for volume of titrant added • p. H meter with silver electrode for end-point detection

Mohr Method • Balance for mass of sample • Buret for volume of titrant added • Indicator for endpoint detection Na 2 Cr. O 4

Mohr Method Cl-1 + Ag+1 Ag. Cl Ksp =1. 82 x 10 -10 Cr. O 4 -2 + 2 Ag+1 Ag 2 Cr. O 4 (brick red) Ksp = 1. 2 x 10 -12 • Must titrate a blank and subtract from total volume of silver nitrate added

Fajans Method • Balance for mass of sample • Buret for volume of titrant added • Indicator for endpoint detection Fluorescein- Adsorption Indicator

Fajans Method Fluorescein

Fajans Method HFl H+1 + Fl-1 (yellow green)

Fajans Method Cl-1 + Ag+1 Ag. Cl Chloride titrated with silver nitrate Cl-1 Ag. Cl Cl-1 Colloidal ppt Before eq pt Ag+1 Ag. Cl Ag+1 Ag. Fl Red Color

Volhard Method • Indirect Method – Back titrate excess Ag+1 • Add excess silver nitrate • Ag+1 + Cl-1 Ag. Cl(s) (white ppt) + Ag+1 • Excess Ag+1 is titrated with standard potassium thiocyanate. • SCN-1 + Ag+1 Ag. SCN(s) • Fe+3 indicator • Fe+3 + SCN-1 Fe(SCN)+2 (red ppt)