Equilibrium distribution ratios have been determined for the extraction of zinc(ll) with 8-quinolinol, 2-methyl-8quinolinol, and 4-methyl-8-quinolinol into chloroform as a function of pH and reagent concentration at 25°C. Except in the case of 2-methyl-8quinolinol, which involved a simple 1:2 chelate, the extractable complexes were 1 :2 chelates to which a third molecule of reagent was coordinated. The overall formation constants of the zinc chelates in aqueous solution have been determined. The distribution coefficients of the chelates and chelate adducts are discussed in terms of structural influences. The analytical advantages of the use of 2-methyl-8-quinolinol in the extraction and subsequent determination of zinc(ll) are outlined.
In continuation of a series of chelatometric titration of metal ion with gallein indicator, two procedures for the EDTA titration of cobalt and nickel using gallein as indicator were proposed. In one procedure cobalt ion was titrated with standard 0.05 M EDTA solution in ammonium chloride buffer by stepwise addition of ammonia to keep the pH at the optimum value of 8. A sharp color change from violet to rose red indicating the end point can be observed. In another procedure nickel ion was titrated with standard 0.05 M EDTA solution at pH 8 to 9 in ammonia‐ammonium chloride buffer solution. The end point is indicated by a color change from bluish violet to rose red.
The interference caused by the presence of approximately equal molar concentration of various foreign ions was observed.
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