Equilibrium constants cobalt chloride complexes

The inertness of the dinuclear complexes is greatest in slightly acidic solutions, which therefore have been employed for the reprecipitation reactions. Apparently the chromium systems are much more labile toward bridge breaking than are the cobalt systems. In aqueous solution the meso-[(en)2Cr(OH)2Ci(en)2] cation (I) enters into a rapidly established (t 1 min. at room temperature) equilibrium with the mono-ju-hydroxo complex [(OHXen)2Cr(OH)Cr(en)2-(HaO)] (n) The equilibrium constant K = [II]/[I] is 0.83 in 1 Af NaC104 at 0°. The salts (dithionate, bromide, chloride, and perchlorate) of the di-p-hydroxo cation are less soluble than the respective salts of the mono-/i-hydroxo cation. It is therefore possible to precipitate the pure salts of the di-/i-hydroxo cation from the equilibrium mixture following the procedure given above. 

Amine-extraction equilibria can also be modeled by chemical-reaction equilibrium constants. Figure 8.3-3 indicates that cations such as iron(III), zinc, cobalt(lI) and copper(II) exhibit high distribution coefficients with chloride solutions, whereas nickel, iron(II), and manganese are not extracted to any great extent. The basis for the differences in distribution coefficients lies mainly in the tendency for the former group of cations to form chloride complexes. Stability constants for these complexes are available in the literature," and they can be used to develop quantitative phase-equilibrium models. 

For TIOA with hydrochloric acid the concentration-based equilibrium constant for salt formation" according to reaction (8.2-6) is 1.51 x 10 and the equilibrium constant for amine-hydrochloride salt dimerization" is 8.0 M Combination of these parameters and the ion-complex stability constants with experimental metal-distribution data allows determination of the equilibrium constants for reactions (8.2-5) or (8.2-7). This completes the description of the amine-metal extraction-phase equilibria. For cobalt(II) in acidic sodium chloride solutions the equilibrium constant" for reaction (8.2-7) with TIOA is 2.0 X 10 and that for coppeifll) is 370 The corresponding value for zinc" is 7.5 x 10 Af -In spile of these relative values, the order of selectivity of TIOA for extraction of the metals is Zn > Cu > Co because of the relative extent of chloride complex formation. For the same reason, zinc stripping is difficult in this system, and copper has a tendency to be reduced to cuprous, which also complexes and extracts extensively. 

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