Abstract
Abstract Results of solubility experiments involving crystalline nickel oxide (bunsenite)
in aqueous solutions are reported as functions of temperature (0 to 350 °C) and pH at
pressures slightly exceeding (with one exception) saturation vapor pressure. These experiments
were carried out in either flow-through reactors or a hydrogen-electrode concentration
cell for mildly acidic to near neutral pH solutions. The results were treated successfully
with a thermodynamic model incorporating only the unhydrolyzed aqueous nickel
species (viz., Ni2+
) and the neutrally charged hydrolyzed species (viz., Ni(OH)02
). The
thermodynamic quantities obtained at 25 °C and infinite dilution are, with 2σ uncertainties:
log10Ko
s0
= (12.40 ± 0.29),ΔrGo
m
= −(70.8 ± 1.7) kJ·mol−1; ΔrHo
m
= −(105.6 ±
1.3) kJ·mol−1; ΔrSo
m
=−(116.6± 3.2) J·K−1·mol−1; ΔrCo
p,m
= (0 ± 13) J·K−1·mol−1; and
log10Ko
s2
=−(8.76±0.15);ΔrGo
m
= (50.0±1.7) kJ·mol−1;ΔrHo
m
= (17.7±1.7) kJ·mol−1;
ΔrSo
m
= −(108 ± 7) J·K−1·mol−1; ΔrCo
p,m
= −(108 ± 3) J·K−1·mol−1. These results are
internally consistent, but the latter set differs from those gleaned from previous studies
recorded in the literature. The corresponding thermodynamic quantities for the formation
of Ni2+ and Ni(OH)02
are also estimated. Moreover, the Ni(OH)
−
3 anion was never observed,
even in relatively strong basic solutions (mOH− = 0.1 mol·kg−1), contrary to the conclusions
drawn from all but one previous study.
