Freezing Potentials in the System H2O–NH3–CO2 at Controlled Concentrations

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  • 1 Geoscience Dept., New Mexico Institute of Mining and Technology, Socorro
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Abstract

Ammonium hydroxide solutions were frozen in a CO2-free atmosphere and freezing potentials were measured. Carbonate-free solutions in the range 5 × 10−6–5 × 10−3 M did not develop appreciable freezing potentials, and neither did solutions with NH3 concentrations ≥4 × 10−4 M that had absorbed CO2 from air. However, if these exposed solutions were diluted, potentials of up to 100 V were observed, depending on the dilution factor and CO2 content. An alternative method of achieving somewhat lower freezing potentials of up to 50 V consisted in reducing the pH with a few drops of relatively concentrated HCl or HF. In the latter case, a reversal of the potential sign was observed when the fluoride concentration was in excess of the dissolved CO2 content. In the system H2O-NH3-CO2 charge separation is influenced by both the hydrogen-ion and overall solute concentrations. The highest potentials occur only when CO2 concentration equals or exceeds that of NH3.

Abstract

Ammonium hydroxide solutions were frozen in a CO2-free atmosphere and freezing potentials were measured. Carbonate-free solutions in the range 5 × 10−6–5 × 10−3 M did not develop appreciable freezing potentials, and neither did solutions with NH3 concentrations ≥4 × 10−4 M that had absorbed CO2 from air. However, if these exposed solutions were diluted, potentials of up to 100 V were observed, depending on the dilution factor and CO2 content. An alternative method of achieving somewhat lower freezing potentials of up to 50 V consisted in reducing the pH with a few drops of relatively concentrated HCl or HF. In the latter case, a reversal of the potential sign was observed when the fluoride concentration was in excess of the dissolved CO2 content. In the system H2O-NH3-CO2 charge separation is influenced by both the hydrogen-ion and overall solute concentrations. The highest potentials occur only when CO2 concentration equals or exceeds that of NH3.

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