Special Features of Aqueous Phosphoric Acid Solutions

2 SPECIAL FEATURES OF AQUEOUS PHOSPHORIC ACID SOLUTIONS [Pg.100]

Like other acids, phosphoric acid (H3PO4) in aqueous solutions dissociates into ions according to [Pg.100]

Unlike other acids, in concentrated phosphoric acid solutions (where the water concentration is low) the hydrogen ions exist not as hydrated ions H+ nH20 but as ions solvated by phosphoric acid molecules H+ nH3P04. For this reason, the conductivity of these solutions is a complex, nomnonotonous function of their concentration. As a conduction mechanism, these ions do not move like a spherical particle in a viscous medium when an electric field is applied to the solution (the Stokes mechanism), but rather, the protons alone jump in the field from one acid molecule to another (the Grotthuss mechanism, suggested as long ago as 1806 as an explanation for the conductivity behavior in aqueous solutions). [Pg.100]

Another special feature of phosphoric acid is its dimerization to H4P2O7 in aqueous solutions at a concentration of about 85 wt% and higher temperatures [Pg.100]

This change is very important for fuel cell operation. Phosphate ions (H2PO4) adsorb well on a platinum catalyst surface, displacing the electrochemical [Pg.100]

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