Abstract
The first acidic ionization constant of Co(II) as cobaltous perchlorate has been determined by a potentiometric titration in a sodium perchlorate medium of constant ionic strength at temperatures ranging from 15 to 40°C and at different concentrations of Co(II) from 2.5 to 25 × 10−3, M and total ionic strength from 0·327 to 0·867.The assembled information indicates the hydrolysis reaction of this ion is a mononuclear reaction where the complex CoOH+ is formed with ΔG 298° = 13·4 ± 0·2 kcal/mole and ΔH298° = 8·2 ± 2·0 kcal/mole.The second acidic ionization constant is higher than the first. This shows that a disproportionation reaction of CoOH+ ions is thermodymanically favoured and has to be considered in the ionic equilibria of aqueous Co(II) ions.
Highlights
THE hydrolysis reaction of Co(II) ion has been investigated by several authors at one given temperature, they obtained figures for the equilibrium constant of that reaction covering the range o f 10- s to 10-12. 1,2,3,4 T h e smallest figure was obtainedbyGayer and Woontnei*, measuring the pH of solutions containing cobaltous chloride
The largest was obtained by Chaberek, Courtney and Martell4 by potentiometric titration of cobaltous chloride in the presence of a large excess of chloride ion
The hydrolysis reaction yields an hydroxo-cobaltous complex ion, which in the simplest case can be represented by the formula in equation (I)
Summary
THE hydrolysis reaction of Co(II) ion has been investigated by several authors at one given temperature, they obtained figures for the equilibrium constant of that reaction covering the range o f 10- s to 10-12. 1,2,3,4 T h e smallest figure was obtainedbyGayer and Woontnei*, measuring the pH of solutions containing cobaltous chloride. The hydrogen-ion concentration due to the hydrolysis reaction and to the perchloric acid initially present in a known amount was measured by potentiometric titration in a suitable cell, employing standard sodium hydroxide solution. The nitrogen purifier was similar to that described by Weissbergers and consisted of an oven with a pyrex tube filled with copper turnings operating at 450°C, and a set of traps with alkaline pyrogallate, concentrated sulphuric acid, ascarite and one filled with the supporting solution to saturate the gas at the vapour pressure of water in this solution, in order to prevent any evaporation from the cell. Nitrogen was bubbled through the cell for 1⁄2hr before readings were taken
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