Abstract
Spectrophotometric methods have been used to determine the stability quotient for the reaction in aqueous acid media. From the nitrate dependence of the molar absorption coefficient it has been shown that the data are best explained by a 1:1 silver(II)-nitrate complex at [HClO4] = 3·12 M, ionic strength 5·63 M and 22·5 ± 1°C with K = [AgNO3+]/[Ag(II)][NO3−] = 0·72±0·10 M−1 at 390 nm, where ϵAgNO3+ = (3·24±0·40) × 103 M−1 cm−1. The absorption coefficient was observed to be acid dependent. The simplest assumption consistent with the experimental results is that the free silver(II) consists of Ag2+ and AgOH+ species. From the acidity dependence we find, at 390 nm, ionic strength 5·63 M and 22·5 ± 1°C that K = [AgNO3+]/[Ag2+][NO3−] ∼ 0·94 M−1 and KH = [AgOH+] [H+]/[Ag2+] ∼ 0·69 M. A variation of absorption coefficient was also observed to occur with changes in the medium. Therefore, the changes in the data obtained in the acid variation are also probably due to the sensitivity of the absorption coefficient and/or K1 to the medium. Attempts to measure the rate of formation of the complex by stopped-flow and temperature-jump were unsuccessful, leading to the conclusion that the rate constant, kf, for the process has a lower limit given by kf ⩾ 4 × 103 M−1 sec−1. The results are discussed and compared with those for other strongly oxidizing metal ions, and other nitrato complexes.