Medical brain notes 14

  INTRODUCTION The oxidation and reduction processes essentially take place simultaneously in a reaction, thus one entity gets reduced in the process of oxidizing the second. ‘Redox’—is the abbreviated form of reduction— oxidation systems. In the  oxidation—reduction methods of analysis  a change in valence of the reacting products is a must which is contrary to precipitation and neutralization methods of analysis where no change in valence occur. The major oxidizing agents normally employed in volumetric titrations include, potassium permanganate, potassium dichromate, and ceric sulphate.

  THEORY As a number of elements are capable of exhibiting more than one oxidation state, hence volumetric titration methods based on redox reactions are usually employed widely.   The phenomenon of oxidation may be explained in the following manner :   (i)            addition of oxygen : Example :   (ii)         removal of hydrogen : Example :    ( iii ) enhancement in the ratio of electronegative to the electropositive portion of the molecule :   Examples :   In the same vein, the process of reduction may also be explained as stated below : ( i ) addition of hydrogen : Example : ( ii ) removal of oxygen :   Example : ( iii ) enhancement in the ratio of electropositive to electronegative portion of the molecule : Example :  [same as under oxidation ( iii ) above] It is quite evident from the above cited examples that reduction need not always imply...

ASSAY METHODS The quantitative estimations of a number of pharmaceutical substances may be carried out by using a variety of potential oxidizing agents as stated below :   ( i )  Permanganate Methods :   ( a ) Direct Titration Methods,   ( b ) Indirect Titration Methods, and   ( c ) Residual Titration Methods.   ( ii )  Dichromate Methods :   Direct titrations with Potassium Dichromate.   ( iii )  Ceric Sulphate Titration Methods :   Direct Titrations with Ceric Sulphate

  PERMANGANATE METHODS   The vital application of potassium permanganate as a potential oxidizing agent in an acidic medium mainly rests on the reactions designated by the following equations :   Chemically we have : Ionically we have :   1. Preparation of 0.1 N Potassium Permanganate Solution   Materials Required :  Potassium permanganate : 3.5 g.   Procedure :  Weigh accurately about 3.2 g of potassium permanganate on a watch-glass. Transfer the   contents to a 250 ml beaker containing cold water and stir vigorously with a glass rod to effect rapid dissolution. Decant the solution through a small plug of glass wool supported by a funnel, into a 1 litre volumetric flask thereby leaving the undissolved residues in the beaker. Add more DW to the beaker and repeat the above process till all the potassium permanganate gets dissolved. Finally make up the volume to the graduated mark and shake well so as to effect uniform mixing.   Note : ( i...