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)