Celebrity Corner of India

  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 ....

  Precipitation Titration The titration in which reaction between titrate and titrant results in the formation of precipitates or slightly soluble ionogens is called precipitation titration. Here the coloured particles floating in the solution is known as precipitates (ppt.)    Types of Precipitation Titration There are basically two types of Precipitation titration: 1. Argentometric Titrations:- ---> The titration in which AgNO 3  is used as titrant is called argentometric titration. 2. Mercurometric Titrations:- ---> When mercuric Nitrate is used as titrant, the titration is called mercurometric titration. ---> It can be used for the estimation of halides (chloride / bromide), thiocynate etc. ---> in this titration, the end point is not clear, so ethanolic medium is used for the titrations. Diphenly carbazone is used as an indicator which imparts blue color at the end of the titration.

Solubility Product Constant   ---> Solubility Product is the product of the concentration of ions of the electrolyte each raised to the power of their coefficients in the balanced chemical equation in a saturated solution. ---> It has a constant value for an electrolyte at a constant temperature. ---> Solubility product constant is denoted by (Ksp) ---> To understand this concept, lets take one example: Consider the saturated solution of FeS in water. The equilibrium is represented by.... The equilibrium constant for above reaction is..... FeS is in solid state and it will not affect the equilibrium constant as it is in its standard state. So, the equilibrium constant is expressed as Ksp (Solubility Product Constant) Where [ Fe ๋ ² ] and [S¯ ² ] represent the concentration of ions in moles/liter. Here the unit of Ksp is (moles/liter) ²  The general precipitation reaction is written as  The unit of Ksp is  (moles/liter)^ a+b ๋ This is called mathematica...