Heat Capacities of Aqueous Solutions of K₄Fe(CN)₆, K₃Fe(CN)₆, K₃Co(CN)₆, K₂Ni(CN)₄, and KAg(CN)₂ at 298.15 K

Abstract

Isobaric volumetric heat capacities of aqueous solutions of K4Fe­(CN)6, K3Fe­(CN)6, K3Co­(CN)6, K2Ni­(CN)4, and KAg­(CN)2 have been measured at 298.15 K over the approximate concentration range 0.02 to 0.4 mol·kg–1 using a Picker flow calorimeter. These data were combined with measured densities to calculate the corresponding apparent molar isobaric heat capacities, C pϕ. The values so obtained were fitted as a function of concentration using an extended Redlich–Rosenfeld–Meyer-type equation to provide the standard state (infinite dilution) quantities, C pϕ o, for each salt. The C pϕ values for all the salts studied showed similar dependences on concentration, with a slight upward curvature at higher molalities, possibly due to anion aggregation. Values of C pϕ o for the aquated cyanometallate anions were estimated using the tetraphenylphosphonium tetraphenylborate extrathermodynamic assumption and were little affected by ion size but were strongly dependent on ionic charge, ranging from −191 J·K–1·mol–1 for [Fe­(CN)6]4–(aq) to +178 J·K–1·mol–1 for [Ag­(CN)2]−(aq). This indicates that the differences between the anions are mostly due to their effect on the surrounding water molecules.

Volumes and Heat Capacities of Cobalt(II), Nickel(II), and Copper(II) Sulfates in Aqueous Solution

“…17 The values of V and Cp so obtained varied smoothly over the investigated concentration ranges (Figures 1-4), with no evidence of the slight 'waviness' often observed in such plots for aqueous electrolyte solutions. 18 For the convenience of potential users, equations that relate  and cp to molality for each of the three sets of solutions are given in the Supplementary Information. -1 , u(T) = 0.01 K, u(p) = 0.001 MPa.…”

Densities and Apparent Molar Volumes of Aqueous Solutions of K4Fe(CN)6, K3Fe(CN)6, K3Co(CN)6, K2Ni(CN)4, and KAg(CN)2 at 293 to 343 K

“…The reagents employed, their treatment, and the solutions prepared from them were identical to those reported previously. 4 Briefly, the cyanometallate salts were the Table 5. continued highest purity available commercially, recrystallized from water where necessary.…”

“…Full specification of reagent sources and purity are exactly as given in Table 1 of the earlier publication. 4 For convenience, this information is repeated as Table S1 in the Supporting Information for this paper. Solutions were prepared by weight using degassed high purity water (Ibis Technology, Australia) and were stored in the dark.…”

“…Dilatometry is generally regarded as being more sensitive and more accurate than other techniques (especially densimetry) for measuring apparent molar volumes at low concentrations and thus for determining standard state volumes at infinite dilution. Last, while a number of volumetric studies of hexacyanometallate salts have been reported, only one determination 6 has appeared for both K 2 Ni(CN) 4 and KAg(CN) 2 .…”

“…For example, such compounds are utilized for mineral flotation, in the recovery of molybdenum, and in analytical chemistry . Other uses of cyanometallate compounds in the food industry, organic synthesis, photography, metallurgy, electrochemistry, health care, and chemistry in general have been summarized in a previous paper and so will not be repeated here.…”