DETERMINAION OF CHLORIDE BY VOLHARD METHOD
This guide explains the Volhard method for determining chloride, involving precipitation titration and the formation of slightly soluble precipitates as endpoints. The process includes standardization of potassium thiocyanate, titration of an unknown chloride solution, and calculations for concentration. Detailed steps and principles are outlined with helpful images.
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Presentation Transcript
DETERMINATION OF CHLORIDE BY VOLHARD METHOD Done by : Sahar Al-Subaie
INTRODUCTION: Precipitation titration is a perfect method for determine halogens and some metal ions. It involves formation of slightly soluble precipitate at end point.
PRINCIPLE: Ag++ Cl AgCl Ag++ SCN AgSCN Fe+ +++ SCN FeSCN++(brown color) end point (white ppt) (back titration)
N.B: The silver thiocyanate (AgSCN) is precipitated before the production of FeSCN 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.
STANDARDIZATION OF POTASSIUM THIOCYANATE (KSCN) : 20 ml AgNO3 80 ml distilled water, mix wel 2 ml con.HNO3, mix well 2 ml Ferric ammonium sulphate,mix well Titrate with Potassium tiocyanate solution until get light brown color (end point).
TITRATION OF UNKNOWN SOLUTION OF CHLORIDE: 5 ml unknown solution of chloride 20 ml D.W, mix well 10 ml AgNO3, mix well (note the white ppt) 1 ml HNO3, mix well 1 ml Ferric ammonium sulphate indicator, mix well Titrate with Potassium thiocyanate until get the light brown color.
CALCULATE THE CONCENTRATION OF KSCN: Ex: If volume of KSCN = 23 M1 x V1 = M2 x V2 MAg+x VAg+= MSCN x VSCN 0.1 x 20 = M SCN x 23 M SCN = 0.087 M
CALCULATE THE CONCENTRATION OF CHLORIDE Ex: If volume of KSCN = 5.3ml 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 = 1 0.46 = 0.54 m moles / 5 ml = 0.108 m moles / ml
