Adsorption at the mercury/formic acid interphase

Abstract

The adsorption of formates and dihydrogen phosphates at the mercury/anhydrous formic acid interphase has been studied by measuring double-layer capacity and electrocapillary curves. Neither HCOO^– nor H₂PO^–₄ ions show positive evidence of specific adsorption, although there is some sign of specific adsorption of cations increasing from Li⁺ to Cs⁺. Cs⁺ appears to be more strongly adsorbed than from aqueous solution. Measurements on HCOONa in HCOOH + H₂O mixtures show that HCOOH is adsorbed slightly more strongly than water with the negative end of the dipole towards the metal at the point of zero charge. Adsorption at the air/solution interphase is similar. Adsorption of di-n-butyl ether from 0.1 M HCOONa in anhydrous HCOOH reaches a maximum at a charge less than –3 µ C cm². Since the effective dipole moment of the ether is small, this is in accord with the orientation of the solvent mentioned above.