SURFACE POTENTIALS OF AQUEOUS ELECTROLYTE SOLUTIONS
NAVAL RESEARCH LAB WASHINGTON DC
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The effect of added electrolytes on the surface potential of water was determined using the radioactive electrode technique. Changes in surface potential were found to vary from 64 mV for Na2SO4 at 1.8m to -180 mV for NaCNS at 7.5m. The Group IA chlorides in water gave surface potential differences that decreased in the order K NH4 Na Li, and the surface potentials of the Group IIA cations decreased in the order Ba Sr Mg. At a constant anion concentration of 2m the surface potential differences due to the sodium salts were in the order SO4-- CO3-- CH3COO- Cl- NO3- Br- I- CNS-. In general the anion with the smaller hydration energy gave the greatest decrease in surface potential. The magnitude of each surface potential change, however, does not appear to be a simple function of the hydration energy or of some related property. The surface potential changes must involve the orientation and structure of the water molecules at the waterair interface, which may be only partially dependent upon the ionic properties as determined in bulk solution.
- Atomic and Molecular Physics and Spectroscopy