In:
Canadian Journal of Chemistry, Canadian Science Publishing, Vol. 69, No. 12 ( 1991-12-01), p. 2112-2116
Abstract:
The fast disproportionation of hexacyanomanganate(III) in acidic medium yields Mn(CN)6 2− and Mn(H 2 O)6 2+ . The reaction has been studied by amperometry, with a rotating platinum-disk electrode, at a 1.0 V (vs. SCE) constant potential, in the acidity range 0.01–2.0 M and at temperatures between −5 and 15 °C. A reversible one-electron process takes place with a 0.85 V (vs. SCE) half-wave potential that is not dependent on acidity. The reaction kinetics is pseudo-first order in [Mn(CN) 6 3− ] and the rate constant depends on acidity according to the equation: k obs = k a + k b [H 3 O + ] + k c [H 3 O + ] 2 . At 5 °C and ionic strength 2.0, the determined values of k a , k b , and k c were (2.20 ± 0.08) × 10 −3 s −1 , (4.9 ± 0.2) × 10 −3 s −1 M −1 and (1.40 ± 0.10) × 10 −3 s −1 M −2 , respectively. A mechanism is proposed where the three terms of k obs are assigned to pathways involving hexacyanomanganate(III) in three different states of protonation. From the effect of temperature the activation parameters, ΔH ≠ and ΔS ≠ , for each pathway are also reported.Key words: hexacyanomanganate(IV), disproportionation, kinetics, amperometry, rotating platinum-disk electrode.
Type of Medium:
Online Resource
ISSN:
0008-4042
,
1480-3291
Language:
English
Publisher:
Canadian Science Publishing
Publication Date:
1991
detail.hit.zdb_id:
1482256-8
