Acid dissociation constants of tetracyanohydroxooxomolybdate(IV) ion

The third dissociation constant of tetracyanohydroxooxomolybdic acid, H3[MoO(OH)(CN)4], has been obtained in the temperature range 25-50°C from the pH-titration curve of its tripotassium salt against hydrochloric acid. The values of pK3 fitted an equation of Harned- Robinson type: pK3 = (1730.72/T)-6.19+0.0308T) obtained by the method of least squares. Thermodynamic quantities ΔG°, ΔH°, ΔS°, and ΔC°p for the process have been evaluated at 30°C.