Ultraviolet spectroscopic determination of the stability constants for copper carbonate and bicarbonate complexes up to the ionic strength of seawater

Abstract

An ultraviolet spectroscopic study at 25°C is used to determine the stoichiometric stability constant of CuCO 3 0 ( β CuCO 3 0 ) over a range of ionic strengths; extrapolation to zero ionic strength provides a thermodynamic constant (log β 0 CuCO 3 0 = 6.89). At 0.69 m ionic strength, log β CuCO 3 0 ) is 6.33. This study provides the first experimental evidence for the existence of CuHCO 3 +. At 0.69 m ionic strength, log β CuHCO 3 + is 2.77. The ultraviolet molal absorptivity spectra for the two complexes are also determined. The spectrum for CuCO 3 0 consists of a single band centered at 276.5 nm and was described well by a Gaussian function. The spectrum of CuHCO 3 + consists of at least two overlapping bands. Side reactions which might affect the data interpretation were included in the analysis of the results. The effects of the Cu(II) hydrolysis reactions were accounted for by using data from previous work, and possible effects due to copper-organic species were eliminated by a subtraction procedure.