The rate of reduction of copper(II) with hydrogen peroxide in seawater

The rates of reduction of copper(II) with H 2O 2 have been measured in seawater solutions as a function of pH (6–9), temperature (5–45°C) and salinity (5 to 35). The rate constants, k, for the reduction d[Cu(II)]/d t=− k [Cu(II)][H 2O 2] have been fitted to the equation log k=2.12+1.29 pH—6534/ T+2.72 I 1/2 with σ=0.13 in log k. At a given salinity, the rates increase as a function of [H +] to the 1.3±0.1 power. Speciation calculations indicate that this slope is related to the concentration of Cu(OH) 2 which is reactive to reduction with H 2O 2. The increase in the rates with increasing ionic strength or salinity is due to the increasing Cl − concentration. The rates increase with increasing chloride to the 1.8±0.2 power. The pH and Cl − results indicate that in seawater the reactive species may be Cu(OH) 2Cl 2 2−. The reaction of the dichloro Cu(II) complex leads to the formation of the dichloro Cu(I) complex, that is resistant to oxidation with O 2 and H 2O 2. Measurements in the major sea salts indicate that the rates in seawater are nearly the same as in NaCl at the same level of Cl − and HCO 3 −. Measurements in NaCl with increasing levels of NaHCO 3 and NaH(OH) 4 at the same pH indicate that CuCO 3 and Cu(CO 3) 2 2− are non-reactive, while CuB(OH) 4 + is reactive to reduction with H 2O 2.