determination of chloride content in water by volhard method

Determination of Chloride content in

water(Volhard Method)

Semester 2ER 1032 – Analytical Methods

Group PresentationDepartment of Earth Resources Engineering

University of Moratuwa

• Content• Introduction about the Chloride ion -• Volhard method -

Principle -• Apparatus -• Reagents -• The procedure of the experiment -

Standardization of thiocyanate solution - Analysis of samples -

• Calculation -• Discussion -• References -

• Introduction about the Chloride ion

Chloride ion in the form of ion Mohr method, fajans method and volhard method

are commonly used to determine chloride concentration in water sample

High chloride ion concentration may harm metallic pipes and structures as well as growing plants.

If concentration of chloride ion in fresh water is less than 1000ppm,we do not detect salty taste in water

The chloride concentration is higher in wastewater than in raw water.

• Volhard method• The Volhard Method is a back(residual) titration and a

precipitation titration that depends on the formation of colored complex ions (colored solution) at the end point.

• The titration is performed only in acidic medium .

•  ion from ferric alum (Ferric ammonium sulfate) acts as an indicator in this practical.

• Brick red is the color at end point.

• The chloride solution is treated with excess of standard Silver nitrate solution,and the residual Silver nitrate is determined by titration with standard Thiocynate solution.

Principle -

White ppt

White ppt

Brick red(End point reaction)

(Back titration reaction)

(Titration reaction)

• Apparatus

• Pipette• Pipette• burettes• conical flasks• Volumetric flask• Volumetric flasks• Quick fit filtration device, wateman filter paper• Water jet pump• Measuring equipments• Bunsen burner

• Reagents(a) Silver nitrate solution

( AgN O3 )=0.100mol L−1

(a) Thiocyanate solution (KSCN )=approximately 0.100mol L−1

(a) Nitric acid solution (HN O3 )=approximately 6mol L− 1

with distilled water

𝑏𝑜𝑖𝑙

(a) Ferric alum indicator solution

{Fe NH 4 (SO4 )2 .12𝐻2𝑂 }(Ferric ammonium sulfate)

{Fe NH 4 (SO4 )2.12𝐻2𝑂 }

𝐷𝑖𝑠𝑡𝑖𝑙𝑙𝑒𝑑𝑤𝑎𝑡𝑒𝑟

• Procedurea) Standardization of thiocyanate solutionStep 1 -

Step 2 -

P inkC olorless

𝐾𝑆𝐶𝑁 solution?

Step 3 -

Color change

Step 4 -

)

C oncentration of KSCN solution (C )=2.5𝑉 1=Cmol 𝐿−1

b) Analysis of samplesStep 1 -

b) Analysis of samplesStep 2 -

Step 3 -

b) Analysis of samplesStep 4 -

𝐹 𝑖𝑙𝑡𝑒𝑟 𝑜𝑓𝑓

𝐹 𝑖𝑙𝑡𝑟𝑎𝑡𝑒

Step 5 - 𝐾𝑆𝐶𝑁 solution𝐶𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛=𝐶𝑚𝑜𝑙 𝐿−1

Step 6 -

𝐶𝑜𝑙𝑜𝑟𝑙𝑒𝑠𝑠→𝐵𝑟𝑖𝑐𝑘𝑟𝑒𝑑Color change

• Calculations

0.11000×𝑉 2mol

𝐶1000×𝑉 3mol

𝐶1000×𝑉 3mol

𝑇𝑜𝑡𝑎𝑙𝑚𝑜𝑙𝑒 𝑜𝑓 Ag+¿ react with Cl−=¿¿ 0.11000×𝑉 2mol−

𝐶1000×𝑉 3mol

=( 0.11000×𝑉 2−𝐶1000

×𝑉 3)× 1000100mol𝐿−1

• Discussion• Why is the titration performed only in acidic medium () ?

In alkaline medium,& ions will be ppted as &

prevent precipitation of other salts like carbonate and sulfide because these salts are soluble in

BUT too high concentration of should be avoided because that destroys the brick red colored ferric thiocyanate complex formed at the end point.

• References• Arnold,E.,Greenberge,S.,Standard Methods for the

Examination of water and wastewater, edition,1992.

• Jeffry,G.H,Bassett,J.,Vogel’s Textbook of quantitative chemical analysis, edition,1999.

• http://ctz116.ust.hk/xyli2/student/courses/CHEM153/labmanual/Chem153_Exp6A.pdf

• http://www.pharma-board.com/fop_drs/drawady/2nd_PartI.pdf

THE END…

Group-5 members

110806L D.L.P.M Dauglas 110807P K.T.D Dissanayaka 110814J M.M Hettiarachchi 110820A S Krishnakumar 110841M C.S.S Senarathna 110885J E.N Lakmali