Diffusion in dilute aqueous solutions of phosphoric acid. Verification of the limiting law for diffusion of weak electrolytes
- 1 January 1984
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society, Faraday Transactions 1: Physical Chemistry in Condensed Phases
- Vol. 80 (11) , 3041-3050
- https://doi.org/10.1039/f19848003041
Abstract
The diffusion coefficient of aqueous phosphoric acid has been measured by a conductimetric technique at 25 °C over the concentration range from 0.0012 to 0.0826 mol dm–3. Below 0.01 mol dm–3 dissociation of neutral H3PO4 molecules to H+ and H2PO– 4 produces a sharp increase in the diffusion coefficient of the phosphoric acid component. When a small correction is included to allow for the association reaction H3PO4+ H2PO– 4⇌H5P2O– 8, the results are in good agreement with predictions based on the limiting law for diffusion of a weak electrolyte. Analysis of the data gives (0.87 ± 0.01)× 10–9 m2 s–1 for the limiting diffusion coefficient of the aqueous phosphoric acid molecule. Within experimental error this value is identical to the limiting diffusion coefficient of H2PO– 4.Keywords
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