ISSN:
1572-8927
Keywords:
Fe(II)
;
oxidation
;
ionic strength
;
NaCl
;
NaClO4
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
Notes:
Abstract The rates of oxidation of Fe(II) in NaCl and NaClO 4 solutions were studied as a function of pH (6 to 9), temperature (5 to 25°C), and ionic strength (0 to 6m). The rates are second order with respect to [H+] or [OH−] and independent of ionic strength and temperature. The overall rate of the oxidation is given by $$d[Fe(II)]/dt = - k[Fe(II)][OH^ - ]^2 [O_2 ]$$ where [OH−]=K W * /[H+](K W * is the stoichiometric dissociation constant for water) and [O 2 ] is the molal concentration of the oxygen. The experimental results were fitted to equations of the form $$log{\text{ }}k = log{\text{ }}k_0 + {\rm A}\sqrt {\rm I} + {\rm A}\sqrt {\rm I} /T + CI$$ where log k0=21.56−1545/T, A=0.470, B=−646, and C=0.723 (σ=0.07) for NaCl; A=−1.638, B=0, and C=0.836 (σ=0.11) for NaClO 4 . The lower results in NaCl at higher ionic strengths are attributed to the formation of FeCl+ that has a slower rate of oxidation. The kinetic results giveβ FeCl = 1.2 ± 0.5, which is in reasonable agreement with literature data. Measurements of the effect of various ions on the rates were studied at constant ionic strength. The results were in the order HCO 3 − 〉Br−〉ClO 4 − 〉Cl−〉NO 3 − 〉SO 4 2− 〉B(OH) 4 − and were attributed to the relative strength of the interactions of Fe 2+ with these anions. The strong interactions of Fe 2+ with SO 4 2− and B(OH) 4 − were used to estimate the stability constants, logβ FeSO 4 = 1.8 ± 0.1 and logβ FeB(OH) 4 = 3.2 ± 0.1, which are in reasonable agreement with literature data.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00664239
Permalink