volhard method presentation to one of the chemistry student by Rawa Abdullah Taha

1. University of zakho
College of science
Faculty of chemistry
Volhard Method
Preparing : Ali Omed
Walid
Supervisor : Dr.Nidhal

2. List of Content
• Argentometric titration
• method of Argentometric titration
• volhard method
• steps of volhard method
• conditions for volhard method
• determination of anions
• application of volhard method
• Advantages of volhard’s method
• limitation of volhard method

3. Argentometric titration
Argentometric is drived for a latin word argentum which means silver
Argentometry is a type of titration involving the silver ion
method of Argentometric titration
Argentometric method involving precipitation titrimetry
• Mohr’s method
• fajan’s method
• Volhard’s method

4. Volhards method
The volhard method was first described by the Jacob volhard a
german chemist in 1874 .
This is an indirect titration procedure used for determining the
anions that precipitate with silver

5. Steps of Volhards method
• Analyte is treated with measured excess of silver nitrate
X+Ag Agx +Ag (excess)
• The unreacted silver ion’s are titrated with a standar
solution of thiocyanate ion using Fe (III) as indicater
Ag+SCN AgSCN
• The first slight excess of thiocynate ion gives red colour
of FeSCN : Fe+SCN FeSCN

6. conditions for volhard method
• The titration must perform in acidic medium to prevente the
precipitation of iron (III) as hydrated oxide
• the indicator concentration should not be more than 0.2 M
• incase of I indicator should not add until all the I is precipitated
with Ag since is would be oxidized by the Fe (III)
2Fe +2I 2Fe+I2

7. conditions for volhard method
• If the Agx precipitation is less soluble than AgSCN they do not need to
Remove ,before titrating with SCN ,such is the case of I`,Br
• If the Agx precipitation are more soluble ,it will react with the titrant ,
which result in the over consumption of SCN and cause the diffuse end point .
such is the case with Cl- :
AgCl + SCN AgSCN + Cl-

8. • To prevent this error the precipitate must be filtered off ,
before titrating withSCN
OR
• Add some volume of organic liquid (like Nitrobenzene, Chloroform)
Which form a film around the precipitates
OR
• Use tartrazine as indicator.

9. Determination of Anions
• Anions whose silver salt are soluble in nitric acid like
(Po4-3,C2O2-2,AsO4-3,Cro4-2,S-2) are precipitated in a neutral solution
With excess of Ag
The precipitate is filtered off , dissolve in Nitric acid and the
Ag titrated with SCN.
OR
The residual AgNo3 in the filtrate is titrated with SCN after acidification
With dilute Nitric acid.

10. Application of volhard method
Volhard method can be used for the determination of
• Halides (Cl-,Br-,l-)
• Anions like (Phosphate,Arsenate,Chromate,Sulphid,Carbonate,Oxalate
• Potassium as potassium tetraphenyl borate
• Flouride as leadChloroflouride

11. Advantages of volhard’s method
• This method is useful where the titrations have be performed at law PH
• The strong acidic environment give advantage for halide analysis because
Ions like carbonate , oxalate and arsenate do not enterfere
• Give accurate results due to back titration.
limitation of volhard method
• Can not be used where the solution has to be neutral .
• Time consuming
• Sometimes adsorption of Ag may give false end point.

12. References
https://en.wikipedia.org/wiki/volhard.method
https://www.britannica.com/science/volhard.method
https://www.scientist.com/chemistry .part.volhard.method
https://www.method.of.Argentometric.titration.com