Chloride Methods
Gravimetric ChloridePotentiometric titrationVisual Indicators
Mohr Method Fajans MethodVolhard Method
In all of these methods the chloride sample is dissolved & reacted with silver nitrate
Cl-1 + Ag+1 AgCl
Gravimetric Chloride
•Use a balance to measure mass of sample and AgCl Precipitate
•No endpoint detection
Potentiometric Titration
• Balance for mass of sample
• Buret for volume of titrant added
• pH 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
Na2CrO4
Mohr Method
Cl-1 + Ag+1 AgCl Ksp =1.82 x 10-10
CrO4-2 + 2Ag+1 Ag2CrO4 (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 AgCl
Chloride titrated with silver nitrate
AgClCl-1Cl-1
Cl-1Cl-1
Cl-1
AgCl
Ag+1
Ag+1
Ag+1Ag+1
Ag+1
Colloidal pptBefore eq pt
AgFl Red Color
Volhard Method• Indirect Method – Back titrate excess Ag+1
• Add excess silver nitrate• Ag+1 + Cl-1 AgCl(s) (white ppt) + Ag+1
• Excess Ag+1 is titrated with standard with standard potassium thiocyanate.
• SCN-1 + Ag+1 AgSCN(s)
• Fe+3 indicator• Fe+3 + SCN-1 Fe(SCN)+2 (red ppt)
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