Standard molar enthalpy of formation of rubidium diphosphate

Rubidium carbonate (Rb2CO3) and ammonium dihydrogen phosphate (NH4H2PO4) were used for synthesizing rubidium diphosphate (Rb4P2O7). The purity of the latter compound was checked up by X-ray diffraction. Rb4P2O7 was involved in an hypothetical reaction and dissolved together with the other components in a 3.85 % (m/m) phosphoric acid solution, using a C-80 SETARAM calorimeter. Mixing processes were also realized in the calorimeter in order to get the standard molar enthalpy of formation of rubidium diphosphate (Rb4P2O7). For that a thermochemical cycle was investigated and the obtained value for the standard molar enthalpy of formation of rubidium diphosphate is (−3,183.7) kJ mol−1. The result is about 1.8 % lower than literature value.