Limiting Conductivities of Strong Acids and Bases in D<sub>2</sub>O and H<sub>2</sub>O: Deuterium Isotope Effects on Proton Hopping over a Wide Temperature Range
Bibliographic record
Abstract
The molar conductivity (Λ°) of hydrochloric acid, potassium hydroxide, and sodium hydroxide has been measured in both light and heavy waters from 298 to 598 K at p = 20 MPa using a high-precision flow-through alternating current (AC) conductance instrument. The results were used to explore the deuterium isotope effect on ionic transport by proton hopping mechanisms under hydrothermal conditions. Extrapolations of published transport number data to elevated temperature were used to calculate the individual ionic contributions (λ°) for H 3 O +, D 3 O +, OH –, and OD –, from which the excess molar conductivities due to proton hopping were calculated. These are the first reported values for the excess conductivities for D 3 O + and OD – at temperatures above 318 K. The excess conductivities indicate a strong deuterium isotope effect whereby the transport of D 3 O + by proton hopping is reduced by ∼33% relative to H 3 O +, and OD – is reduced by over 60% relative to OH –, over the entire temperature range. A well-defined maximum in the excess conductivities of D 3 O + and H 3 O + at ∼420 K suggests that the Eigen cation (H 2 O) 4 H + and the Zundel transition-state cation (H 2 O) 2 H + are destabilized at elevated temperatures as the three-dimensional, tetrahedrally hydrogen-bonded networks in water break down. The less pronounced maximum for OD – and OH – suggested that their Eigen and Zundel anions, (H 2 O) 3 OH – and (H 2 O)OH –, are less destabilized in the two-dimensional networks and chains that dominate the “structure” of liquid water under these conditions.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 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 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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 source (direct Gemma or distilled Codex), 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".