Abstract
N-(2-Pyridyl)-N', C-diphenylformazane (PPF), N-(2-benzothiazolyl)-N', C-diphenylformazane (BTPF) and N- (5-nitro-2-pyridyl)-N', C-diphenylformazane (NPPF) were proposed as possible reagents for the determination of small amounts of copper and nickel.
The reagents were acid-base indicators which were present in the three forms in the solutions. The dissociation constants in dioxane solutions at various concentrations were determined spectrophotometrically. It was found that the acid dissociation constants vs. mole fraction of dioxane plots were linear and the values at zero dioxane mole fraction were calculated by an extrapolation.
The reagents formed blue chelates with copper and nickel ions in aqueous dioxane in the metal to reagent ratio 1 to 1 in the presence of an excess metals. The compositions of copper chelates were determined by the continuous variations method and their equilibrium constants were determined spectrophotometrically at 30°C at various concentrations of dioxane. The constants were found to be proportional to the mole fraction of dioxane and the experimental equation were calculated.
The extraction of copper as a NPPF or BTPF chelate into carbon tetrachloride was also investigated by keeping the ionic strength constant by sodium perchlorate at 30°C. The compositions of the copper chelates extracted into carbon tetrachloride were determined by the continuous variations method and was found to be in the 1 to 2 copper to reagent ratio. The extraction of the copper chelates followed a normal procedure; two reagent molecules added and two proton released on chelation which indicates the formation of a 1 to 2 neutral chelate. PPF decomposed slightly in the course of extraction in the presence of copper, but NPPF and BTPF were more stable than PPF in this respect.
New measurements were reported for the values of the correction term log UH, μ=0.1 and 30°C which must be added to pH meter readings in solution of aqueous dioxane at mole fraction n2 00.3863 in order to give the true concentration of hydrogen ion.
