Date post: | 15-Apr-2017 |
Category: |
Engineering |
Upload: | prasad-madushanka |
View: | 2,902 times |
Download: | 7 times |
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