Mohr's Method and its Limitations
Mohr's method Formation of coloured ppt Mohr's method of determination of chlorides and bromides by titration with silver nitrate. PRINCIPLE: The method involving end point detection by formation of an orange red precipitate of silver chromate (after the precipitation of AgCl is complete) using potassium chromate as an indicator is called Mohr's Precipitation titration method. chloride ion sample ---> dissolved in water ---> titrate with AgNO 3 ---> formation of white AgCl ppt. At the end point, excess drop of silver nitrate reacts with indicator and forms the orange red coloured ppt of Silver chromate. The concentration of the indicator is important. The silver chromate should start precipitating at the equivalence point, where we have the saturated solution of AgCl. From Ksp, the concentration of Ag+ at the equivalence point is 10¯⁵ M. Ksp for Ag 2 CrO 4 = 1.1 x 10¯¹² Ksp = [Ag+] ² . [CrO 4 ¯ ² ] (∵Ag₂CrO 4 ) ∴ 1.1 x 10¯¹² = ( 10¯⁵) ² ....
Comments
Post a Comment