The molal acid dissociation ("hydrolysis") constant Km of aqueous hexaaquochromium(II1) ion, at 25.0" and ionic strength 0.5 m, has been determined spectrophotometrically as a function of pressure P up to 3 kbar. K m increases with P (kbar) in accordance with the equationIn K,,, = 0.151 P -9.474The molal volume change is -3.8 + 0.7 cm3 mole-', and the enthalpy and entropy changes at 1 bar are 9.3 kcal mole-' and 12.1 cal deg-I mole-'. Compressions of 0.1, 0.5, and 1.0 M aqueous perchloric acid, lithium perchlorate, and sodium perchlorate up to 4 kbar have also been measured.Canadian Journal of Chemistry, 48, 3223 (1970) Introduction ambient temperature over a convenient period The experimental data relating to the effect of time without complications arising from of pressure on the dissociation of electrically hydrolytic polymerization (reaction 5), which is neutral weak acids (eq. 1) and bases (eq. 2) in essentially a substitution process. aqueous solution have been reviewed by Hamann [51 2Cr(HZ0)50HZ+ = (HZ0)4Cr(OH)zCr(OHz)44+

The stabilities of aqueous solutions of typical salts of manganese(II), iron(II), cobalt(II), cobalt(III), nickel(II), and copper(II) at temperatures up to 300 °C have been investigated. At 200 to 300 °C, hydrolysis of the metal ions can lead to the partial precipitation of metal oxides, or silicates in the cases of nickel(II) and cobalt(II) when a silica vessel is used; except for the M(II) sulfates, which precipitate as MSO4•H2O (M = Mn, Fe, Co, and Ni) and Cu3SO4(OH)4. Manganese(II), iron(II), and cobalt(II) tend to be oxidized at 250 to 300 °C in neutral or acidic solutions, while cobalt(III) in aqueous ammonia is reduced. Aqueous CuCl2 is in equilibrium with CuCl and Cl2 at 300 °C. Hydrolytic precipitation is suppressed by the addition of small concentrations of hydrogen ion or larger concentrations of chloride ion, if oxidation–reduction processes do not interfere.