EXPERIMENT 6 Determination of Chloride by Volhard Method :Objective of this experiment Determination of chloride in an unknown) a( .solution .Determination of chloride in an unknown salt) b( :Principle The chloride present in the unknown are precipitated by* adding an excess amount of standard Silver Nitrate
.solution The un reacted silver nitrate is determined by back* titration with a standard solution of Potassium Thiocyanate using Ferric Ammonium Sulphate as .indicator Ag+ + Cl Ag+ + SCN Fe+ ++ + SCN AgCl (white ppt) AgSCN (back titration)
FeSCN ++ (brown color) end point The silver thiocyanate (AgSCN) is precipitated before the* production of FeCNS because of the very small solubility .product of the silver thiocyanate Concentrated Nitric Acid is added to prevent hydrolysis of* .the Ferric Ammonium Sulphate which used as indicator :Reagent .Standard 0.1 N Silver Nitrate (AgNO3)- 1 .N Potassium Thiocyanate (KSCN) 0.1- 2 .Con. Nitric Acid (HNO3)- 3
. Ferric Ammonium Sulphate- 4 .Unknown solution of Chloride- 5 :Procedure I) Standardization of Potassium Thiocyanate (KSCN) ml AgNO3 20- 1 ml distilled water, mix well 80- 2 3- 2 ml con.HNO3, mix well 4- 2 ml Ferric ammonium sulphate, mix well
Titrate with Potassium- 5 tiocyanate solution until get light brown color (end .point) II) Titration of unknown solution of chloride ml unknown solution of 5- 1 chloride ml D.W, mix well 20- 2
ml AgNO3, mix well (note 10- 3 the white ppt) ml HNO3, mix well 1- 4 ml Ferric ammonium 1- 5 sulphate indicator, mix well Titrate with Potassium- 6 thiocyanate until get the .light brown color
:Calculation a) calculate the concentration of KSCN Ex: If volume of KSCN react in standardization of KSCN = 23 M1 x V1 = M2 x V2* MAg+ x VAg+ = MSCN x VSCN x 20 = M SCN x 23 0.1 M SCN = 0.087 M b) calculate the concentration of chloride Ex: If volume of KSCN react in standardization of Chloride = 5.3 Total m moles of Ag+ = M x V*
T = 0.1 x 10 = 1 m moles Un reacted m moles of Ag+ (m moles of KSCN used) = MKSCN x VKSCN * U = 0.087 x 5.3 = 0.46 m moles Reacted m moles of Ag (m moles of Chloride) = T U * 0.46 1 = m moles / 5 ml 0.54= m moles / ml 0.108=
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