The kinetics and mechanism of Hg 2+ -catalyzed substitution of cyanide ion in an octahedral hexacyanoruthenate(II) complex by nitroso-R-salt have been studied spectrophotometrically at 525 nm (λ max of the purple-red-colored complex). The reaction conditions were: temperature = 45.0 ± 0.1 • C, pH = 7.00 ± 0.02, and ionic strength (I) = 0.1 M (KCl). The reaction exhibited a first-order dependence on [nitroso-R-salt] and a variable order dependence on [Ru(CN) 6 4− ]. The initial rates were obtained from slopes of absorbance versus time plots. The rate of reaction was found to initially increase linearly with [nitroso-R-salt], and finally decrease at [nitroso-R-salt] = 3.50 × 10 −4 M. The effects of variation of pH, ionic strength, concentration of catalyst, and temperature on the reaction rate were also studied and explained in detail. The values of k 2 and activation parameters for catalyzed reaction were found to be 7.68 × 10 −4 s −1 and E a = 49.56 ± 0.091 kJ mol −1 , H = = 46.91 ± 0.036 kJ mol −1 , S = = −234.13 ± 1.12 J K −1 mol −1 , respectively. These activation parameters along with other experimental observations supported the solvent assisted interchange dissociative (I d ) mechanism for the reaction.
The kinetics of mercury(II)-catalyzed substitution of cyanide ligand in hexacyanoruthenate(II) by pyrazine (Pz) has been investigated spectrophotometrically at 370 nm in aqueous medium. The reaction exhibits firstorder dependence on [Pz] at low concentrations, then reaches a maximum value, and finally decreases at high [Pz]. The reaction has a variable-order dependence in [Ru(CN) 64-], unity at lower [Ru(CN) 6 4-], and fractional order, not tending to zero order at higher [Ru(CN) 64-]. The effects of pH, ionic strength, concentration of catalyst, and temperature variations have been studied. The activation parameters for the reaction were calculated. We propose a solvent assisted interchange dissociative (I d ) mechanism for the reaction.
A sensitive, simple and rapid spectrophotometric method for the determination of mercury (II) based on its catalytic effect on the abstraction of coordinated cyanide from hexacyanoferrate (II) by pyrazine has been developed using fixed time procedure. The extent of the reaction is monitored spectrophotometrically by measuring the increase in absorbance at λ max =440 nm of the yellow colored complex, [Fe(CN) 5 Pz] 3under the reaction conditions; [Fe(CN) 6 ] 4-=7.2×10 -3 mol L -1 , [P z ]=3.75×10 -4 mol L -1 , temperature=25.0±0.1 °C, pH= 2.50±0.02 and I=0.1 mol L -1 (KNO 3 ). The experimental rate data under the conditions used in the present study exhibited a linear dependence between absorbance and [Hg 2+ ] catalyst in the range 5.065-50.15 ng mL -1 . The detection limit is found to be 4.01 ng mL -1 . The maximum relative standard deviations and percentage errors for mercury(II) determination are found to be 2.2 and 3% respectively. The percentage recoveries are found to be in the range of 99-102%. Analytical data for determination of mercury(II) is presented together with the application of proposed method in water spiked synthetic mixtures. The validity of the proposed method is tested by comparing the results obtained by present method with atomic absorption spectrometry.
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