4780
HARRYFREUND AXD C.IRL R. SCHNEIDER [CoSTRlBUTlOSFROM
THE
DEPARTMEST O F CHEMISTRY, O R E G O S
1:01. s1
STATE C O L L E G E ]
Determination of the Cumulative Dissociation Constant of Tetracyanonickelate (11) Ion BY HARRYFREUND AND CARLR . SCHNEIDER RECEIVED JAYUARY 31, 1959 The ultraviolet absorption a t 267 2 mfi provided a unique means of quantitatively determining Si(CS),'. Equilibration of nickel perchlorate and potassium cyanide systems, buffered at varying pH levels and ionic strengths, permitted evaluation of the cumulative dissociation constant uf thc cornplev At 24 92' the cumulative cunstant was found to be (1 0 f 0 2 ) X 10 3 1
Introduction No satisfactory experimental value for the dissociation constant of the tetracyanonickelate(I1) species has been determined. Hume and Kolthoff reviewed the early investigations and indicated the values to be unreliable. Irreversibility precluded the use of thermodynamic calculations based on measured e.m.f. values. Polarographic studies on 0.1 &! solutions of potassium tetracyanonickelate(I1) in water failed to reveal an anodic wave due to cyanide. Assuming cyanide in the molar range to be detectable, the dissociation constant of the complex would have a maximum value of This was taken as a confirmation of Latimer's2 value of 10-22 a t 25' which was calculated from thermodynamic data. Recently Duodoroff on the basis of toxicity of nickel-cyanide systems to certain aquatic life, suggested a dissociation constant of approximately 1I) -30. It was the purpose of this research to determine accurately the cumulative dissociation constant of the tetracyanonickelate(I1) species. If in a system containing low concentrations of nickel and cyanide, the principal species present in solution are Ni++, Ni(CN)*=, CN- and HCN, then the equations governing the relative amounts are
would therefore be strained and not exist in significant quantities. The hydrolysis of aquonickel ion is known to occur with the formation of monohydroxy and likely even more extensively hydrolyzed species including p o l p m e r ~ . ~ The need for p H control led to the use of acetate and phosphate buffers and the need for information on aceto and phosphato complexes of nickel. Evidence for orthophosphate complexation has not been reported.lOmll;Iceto complexes of nickel are well k n ~ w n ' ~and , ' ~ corrections must be applied when acetate buffers are employed. Experimental conditions were selected either to eliminate, minimize or provide data so that corrections could be made. Experimental
Xickel perchlorate was prepared by fuming either nickel nitrate hexahydrate or nickel carbonate with perchloric acid. Stock solutions 0.05 and 0.0064 31 in nickel perchlorate were standardized with diniethy1glyoxinie.l~ Stock solutions 0.10 and 0.05 df in potassium cyanide were prepared by dissolving the salt in water. The Liebig titration as modified by D&nig&swas used for ~tandardization.'~ Stock potassium acetate, acetic acid buffers were 0.080 111 in total acetate. Stock potassium hpdrcgen phosphate, potassium dihydrogen phosphate buffers were 0.1 or 0.5 Jf in total phosphate and contained sufficient potassium perchlorate to facilitate ionic strength adjustment. Stock solutions 0.1 J i' in potassium perchlorate w r e preTotal cyanide = 4(Ki(CSI=) ( C S - ) -I-( H C S ) (1) pared. A Beckman Model DU Quartz spectrophotometer with Total nickel = ( S i ( C S ) J = ) (Xi+*) (2) matched 1 cm. silica cells was used. K , = (H+)(CN-)/(HCS) (3) A Beckman Model H-2 meter was used for pH determinations. The readings of the glass electrode-calomel pair were K n = (Si++)(CS-)4/Si(C?;)(' (-1) calibrated against standard PH buffer solutions, as described The ultraviolet absorption spectrum of the tetra- by Bates.'G cyanonickelate(I1) species has been r e p ~ r t e d ~ ' ~X constant temperature bath operating at 24.92 dz 0.05" used for equilibration. and used by several investigators for the determi- was Beer's law was found to hold at 267.5 and 285 mp over nation of nickel6,' to the nickel perchlorate coucentration range of 8.62 X Stepwise formation of tetracyanonickelate(I1) 8.62 X 10-5 M iii 0.02 Af potassium cyanide. The molar from aquonickel could result in the formation of absorptivities found were 11,680 i 40 a t 267.5 mfi and dz 70 a t 285 mp. The precision measure is expressed 3s several intermediate complexes, yet no such species 4,590 absolute standard deviation. have been reported. A structurally discontinuous The molar absorptivity was checked by other workers change occurs in going from the tetrahedral aquo during these investigations. The mean value a t 267.5 r n f i
+ +
ion to the square planar tetracyano ions8 Intermediate species must conform to either the tetrahedral or square planar structures and (1) D . N. H u m e and I. hI. Koithoff, Tars J O U R N A L , 72, 4-123 (1950). ( 2 ) U'. SI. Latimer, "Oxidation Potentials," 2nd ed., PrenticeHall, Inc., h-ew York, S . Y . , 1952, p. 200. (3) P. Duodoroff, Sewage and Znd. Wastes, 28, 1020 (1956). (4) B. Major, Acta Cniz'. S z e g e d i e n s i s S p c f . S r i . H a l . A c f a Chem. el P h y s . , n.s.v.1.. 17 (1942). (,5) R. P. Buck, S. Singhadeja and L. B. Rogers, Awal. C h e m . , 26, 1240 (1954). (0) B . D. Brummet and R . hl. Hollweg, ibid., 28, 887 (1956).
(7) T . S. Soine, M.S. Thesis, Oregon State College, Corvallis, Oreg o n , 1937. (8) K . S. Pitzer, "Quantum Chemistry," Prentice-Hall, Inc.. Srm Y. G. Sillen, "Stability Constants," Vol. I , Special Publication K O .7 , T h e Chemical Society, Burlington House, London W. 1. 1965, p . 13. (10) J. A. R. Genge, A. Hulroyd, J . E . Salmon and J . G . I,. R'all, ci2Pmistr3' n7td Illdlrslry, 387 (1955) (11) J , R . Van Wazer and C. I;. Callis, Che7n. Revs., 58, 1011 (1058). (12) St. Fronaeus, A c f a Chem. S r a ~ d . 6, , 1200 (1952). (13) A. E. Martell and R . C. Plumb, J . P h y s . C h ~ m . 56, , 993 (1952). 114) \V I;. Hillebrand, G E. I;. I,undell, H . A. Bright and J. I. Hoffman, "Applied Inorganic Analysis," 2nd Ed., John Wiley and
thods of Chemical AnalyPrentice-Hall, Inc , S e w Y o r k , S . Y , , 1952, pp. 370-373, 110) R. G. Rates. "Iilectrometric p H Determinations," J o h n Wilpy o n d Pons, I n c . , S e n Y o r k , N . Y . , 1
