Third dissociation constant of phosphoric acid in H<sub>2</sub>O and D<sub>2</sub>O from 75 to 300 °C at <i>p</i> = 20.4 MPa using Raman spectroscopy and a titanium-sapphire flow cell
Bibliographic record
Abstract
A custom-built titanium-sapphire flow cell has been used with a confocal Raman microscope to collect solvent-corrected reduced isotropic spectra of sodium and potassium phosphate solutions in light and heavy water from 75 to 300 °C at 20.4 ± 0.4 MPa over a wide range of concentrations. The symmetric vibrational modes of PO43- and HPO42-/DPO42- in both solvents broadened and moved to lower wavenumbers with increasing temperature, suggesting that oxyanion-water hydrogen bond strengths increase at elevated temperatures. Raman scattering coefficients, measured relative to the trifluoromethanesulfonate ion, were used to determine thermodynamic equilibrium quotients for the reaction PO43- + H2O ⇌ HPO42- + OH- and its deuterium counterpart. Standard-state acid ionization constants were calculated using a modified Pitzer model and fitted as a function of temperature and solvent molar volume over the range of 25 to 300 °C from psat to 20 MPa. The deuterium isotope effect on the chemical equilibrium constant, ΔpK3a,m = pK3a,D,m - pK3a,H,m, was found to decrease from 1.045 ± 0.046 at 25 °C to 0.898 ± 0.073 at 250 °C. This behaviour is consistent with a model in which zero-point energy effects dominate at low temperatures and long-range solvent polarization becomes increasingly important as the temperature increases towards the critical point of D2O. These are the first experimental ionization constants to be reported in the literature for this reaction in light water above 50 °C and in heavy water at any temperature.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".