Kinetics and Mechanism of Oxidation of Formic Acid by Chromium(VI). Inhibition by Manganese(II) Ion

1992 ◽  
Vol 57 (9) ◽  
pp. 1821-1835 ◽  
Author(s):  
Conchita Arias ◽  
Joaquin F. Perez-Benito
Keyword(s):  
Formic Acid ◽  
The Other ◽  
Hydrogen Ion ◽  
Acid Solutions ◽  
Acid Media ◽  
First Order ◽  
Chromium Vi ◽  
Acid Reaction ◽  
Aqueous Perchloric Acid ◽  
Mechanism Of Oxidation

Experiments have been done to clarify the mechanism of the chromium(VI)-formic acid reaction in aqueous perchloric acid media, both in the absence and in the presence of manganese(II) ion. Two mechanisms are proposed, one for slightly acid solutions (I) and the other for strongly acid ones (II). Both mechanisms are first order in both oxidant and reductant, but they differ in the order to hydrogen ion (1 for mechanism I and 3 for mechanism II). The activation energy for mechanism I (60.4 ± 0.9 kJ mol-1) is considerably higher than that for mechanism II (41.2 ± 0.4 kJ mol-1). The rate-controlling steps proposed for mechanisms I and II are the H2CrO4-HCOOH and HCrO3+-HCOOH2+ reactions, respectively. Mechanism I is inhibited by manganese(II) ion, but mechanism II is not, which suggests that mechanism I involves Cr(IV) as an intermediate, whereas mechanism II does not.

scholarly journals The Hydrogen Ion Concentration in the Gut of certain Lamellibranchs and Gastropods

1925 ◽  
Vol 13 (4) ◽  
pp. 938-952 ◽  
Author(s):  
O. M. Yonge
Keyword(s):  
Mantle Cavity ◽  
Mya Arenaria ◽  
Hydrogen Ion ◽  
Ion Concentration ◽  
Pecten Maximus ◽  
Hydrogen Ions ◽  
Acid Media ◽  
Hydrogen Ion Concentration ◽  
Acid Reaction ◽  
Acid Region

1. In the Lamellibranchs, as typified by Pecten maximus, Mya arenaria and Ensis siliqua, the entire, gut has an acid reaction, the stomach being the most acid region and the pH rising along the mid-gut and rectum.2. The origin of the acidity of the gut lies in the style. This has a low pH (5·4 in Pecten and Mytilus, 4·6 in Ensis and 4·45 in Mya), and, after it has been artificially extracted from Mya or induced to disappear, by keeping the animals under abnormal conditions, in Mytilus, Tapes and Pecten, the pH of the stomach invariably rises (by as much as 0·825 in Mya and 0·72 in Tapes), although the pH in the mantle cavity has fallen.3. The style, which dissolves rapidly in alkaline or weakly acid media, is not dissolved in fluids below a certain pH—4·4 for Ensis, 4·2 for Mya, 3·6 for Pecten and Mytilus.4. The style is never absent, even though animals are starved, so long as they are kept under otherwise healthy conditions. The disappearance of the style under abnormal conditions is probably due to a lowering of the vital activities, which include the secretion of the style substance, and the consequent dissolution of the style by the less acid contents of the stomach.5. The style is only maintained as a result of a balance between the rate of its secretion and the rate of its dissolution.6. There is a well-marked correlation between the tolerance of the presence of hydrogen ions possessed by the cilia from the various regions of the gut and the degree of acidity of the fluid with which they are normally surrounded.7. The pH of the gut in five Gastropods has been investigated. The fore-gut and stomach have invariably the lowest pH.8. This acidity may be caused by the salivary glands (Patella and Buccinum), the digestive gland (Doris and Aplysia), or the style (Crepidula).9. The mid-gut and rectum have a high pH, except in Doris, where there is little secretion of mucus, the gut being free and muscular.10. The style of Orepidula has similar properties to those of the Lamellibranchs. It has a pH of 5·8, and is not dissolved in fluid of pH 3·6 or lower.11. The cilia from the gut of Buccinum and Doris can function in a pH of 5·0, but there is little difference in the toleration of the various cilia to the presence of hydrogen ions.

Kinetics and Mechanism of Oxidation of Selenium(IV) by Permanganate Ion in Aqueous Perchlorate Solutions

1993 ◽  
Vol 58 (3) ◽  
pp. 538-546 ◽  
Author(s):  
Refat M. Hassan ◽  
Sahr A. El-Gaiar ◽  
Abd El-Hady M. El-Summan
Keyword(s):  
Reaction Mechanism ◽  
Reaction Rate ◽  
Oxidation Process ◽  
Selenium Dioxide ◽  
Order Reaction ◽  
Acid Solutions ◽  
First Order ◽  
Acid Catalyzed ◽  
Mechanism Of Oxidation ◽  
Kinetics Of

The kinetics of permanganate oxidation of selenium dioxide in perchloric acid solutions at a constant ionic strength of 2.0 mol dm-3 has been investigated spectrophotometrically. A first-order reaction in [MnO4-] and fractional order with respect to selenium(IV) were observed. The reaction rate was found to be pH-independent at lower acid concentrations ([H+] < 0.5 mol dm-3) and was acid-catalyzed beyond this range. Addition of Mn2+ and F- ions leads to the prediction that MnO4- is the sole reactive species in the oxidation process. A tentative reaction mechanism consistent with the reaction kinetics has been proposed.

Cooxidation of formic acid and oxalic acid by chromium(VI) in aqueous acid media: a kinetic study

2001 ◽  
Vol 2001 (8) ◽  
pp. 334-335 ◽  
Author(s):  
Asim K. Das ◽  
Aparna Roy ◽  
Bidyut Saha ◽  
Mahua Das
Keyword(s):  
Oxalic Acid ◽  
Formic Acid ◽  
Kinetic Study ◽  
Acid Media ◽  
Aqueous Acid ◽  
Chromium Vi
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