Copper(II) Complexation by Fulvic Acid Extracted From Sewage Sludge as Influenced by Nitrate Versus Perchlorate Background Ionic Media
1979
Sposito, Garrison | Holtzclaw, Kenneth M.
The possible adverse effect of CuNO₃⁺ ion pairs on studies of the complexes formed between Cu(II) and fulvic acid extracted from sewage sludge was investigated by potentiometric titration of 2 × 10⁻³M K/H fulvate with Cu(NO₃)₂ and Cu(C10₄)₂, at pH 5 and 25°C, in ionic media of 0.1M KNO₃ or KC10₄, respectively. It was shown that the degree of complexation of Cu²⁺ in the NO₃ medium was always significantly greater than that in the C10₄ medium for total Cu concentrations in the range 10⁻⁴M to 10⁻²M. This result was interpreted as evidence for significant concentrations of CuNO₃⁺ ion pairs and mixed CuNO₃-fulvate complexes in the NO₃ medium. Further support for the existence of CuNO₃⁺ in the NO₃ medium was obtained through a successful calculation of the thermodynamic stability constant for this ion pair that employed data from blank titrations with Cu(NO₃)₂ and Cu(ClO₄)₂. It was concluded that ClO₄ ionic media should be used instead of NO₃ ionic media in studies of Cu(II) complexation with the functional groups of fulvic acid.
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