Abstract
The Raman spectrum of aqueous phosphoric acid has been investigated at apparentconcentrations of 0.3 to 9.7 mol-dm−3 at 25°C. A quantitative analysis hasbeen made over this concentration range after the determination of the responsecoefficients of the H2PO− 4 and H3PO4 species. In the first step, the spectra wereinterpreted assuming that only two species (H2PO− 4 and H3PO4) were present inthe system. The dissociation of phosphoric acid obtained in this case is consistentwith the values Preston and Adams(1) obtained, and which was also found fromRaman spectroscopy. However, a discrepancy exists between the representationsfrom spectra and experimental ones. This discrepancy can be removed if anotherspecies, the anionic dimer H5P2O− 8 is taken into account. Therefore, in the secondstep, a modified interpretation of the spectra, was used to determine theconcentrations of the H2PO− 4, H5P2O− 8, and H3PO4 species and to deduce the correspondingdegree of dissociation of the acid, as well as the speciation of the solutions as afunction of the apparent concentration of phosphoric acid. As in the results Elmoreand co-workers,2 which were deduced from pH measurements, the degree ofdissociation reaches a minimum and then increases significantly for apparentphosphoric acid concentrations greater than 1 mol-dm−3.
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Cherif, M., Mgaidi, A., Ammar, N. et al. A New Investigation of Aqueous Orthophosphoric Acid Speciation Using Raman Spectroscopy. Journal of Solution Chemistry 29, 255–269 (2000). https://doi.org/10.1023/A:1005150400746
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DOI: https://doi.org/10.1023/A:1005150400746