Abstract

KINETIC ESTIMATION OF SILVER IN TRACE AMOUNTS BY ITS CATALYTIC EFFECT ON LIGAND SUBSTITUTION REACTION BETWEEN HEXACYANOFERRATE (II) AND DPQ

Dr. Anupma Singh*, R. M. Naik, Dr. Neha Agarwal

ABSTRACT

The Silver is known to catalyse the reaction between hexcyano ferrate (II) and DPQ in the concentration range 3.8x 10 -7 to 3.8 10-8 M. The DPQ is substituted in hexacyanoferrate (II) by replacing one of the cyanide co-ordinated in the coordination sphere to Iron (II) in hexacyanoferrate (II) ion. A catalytic Kinetic Method based on fixed time procedure has been developed for estimation of Silver by following the progress of the reaction spectrophotometrically at 547 nm. The reaction conditions chosen for the progress of the reaction were: Ionic strength I = 0.1 M (KNO3), Temp= 25.0 ± 0.1oC and pH = 3.0 ± 0.02. On the basis of experimental results for the catalyzed reaction the following rate expressions was derived:-d[Fe(CN)5DPQ]3-dt = k’ [Fe(CN)6]4- + k’2 [Ag+]In this equation k' is the rate constant for uncatalysed path when a non rate limiting concentration of DPQ was taken and k'2 is composite rate constant. The absorbance changes were recorded at every fifteen minutes for the reaction under experimental condition [Fe(CN)6]4 - =5.5 x 10-3 M and [DPQ] = 2.5x10-4M at each Silver concentration in the range (3.0x10-7 to 3.0x10-8M).The plot of absorbance versus[Ag]1+ concentration yields a straight line following equation A15 = 3.3x105 [Ag]2++0.09. The detection limit is evaluated by standard procedure and is found to be 2.5x10-7M in [Ag+1]. The concentration of [Ag]+ was also estimated in presence of several other interfering and non interfering cations and anions.

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