| Abstract [eng] |
At least three poorly soluble compounds can be formed in the CuSO4 – K4P2O7 – H2O system: a single salt Cu2P2O7.5H2O and two dimorph’s both having chemical formula Cu3K2(P2O7)2.3H2O. A previously known form of Cu3K2(P2O7)2.3H2O (we named it Dimorph A) transforms into a novel Dimorph B, which has a different structure. The similarities between the XRD patterns and vibrations spectra of copper–ammonium and copper–potassium Dimorph’s B imply that they are isostructural. The values of the angle for copper–potassium and copper–ammonium salts and Cu2P2O7.5H2O are relatively low and vary within a narrow range (123.1 – 127.1°). The formation of the compounds significantly depends on the conditions of the experiment. A double salt in the CuSO4 – K4P2O7 – H2O system may be formed after some time in the reaction mixture as a result of the following heterogeneous reaction: 3Cu2P2O7∙5H2O↓ + H2P2O72– + 4K+ → 2Cu3K2(P2O7)2∙3H2O↓ + 2H+ + 9H2O This reaction has not been previously described for any polyphosphate system. Therefore, novel results of scientific investigation are presented. The rate, duration and yield of heterogeneous reaction substantially depend on pH of the solution, [Cu2+ + P2O74–] and n ([P2O74–] / [Cu2+]). At a relatively low pH the induction time is high, the reaction rate is low and duration is long. The maximal yields close to 100% can be achieved when [Cu2+ + P2O74–] = 0.1 M. At increased pH values, the induction time, the yield and duration of the reaction diminish. At increased [Cu2+ + P2O74–] the induction time and duration of heterogeneous reaction also diminish. Reduction of n from 1 to 0.67 results in the substantial increase of both the induction time and duration of the reaction, while the yield notably diminishes. Analogous heterogeneous reaction proceeds in the CuSO4 – (NH4)4P2O7 – H2O system. Formation of the precipitates in the CuSO4 – K4P2O7 – H2O and CuSO4 – (NH4)4P2O7 – H2O systems proceed in the same order: semiamorphous voluminous precipitates → Cu2P2O7.5H2O → Cu3Kat2(P2O7)2.3H2O (Dimorph A) → Cu3Kat2(P2O7)2.3H2O (Dimorph B), where Kat = K or NH4. |
