Volhard Method

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