| "Rapid Determination of Boric Acid in Nickel Plating Solution" by the addition of Na₂C₂O₄and thus preventing the precipitation of Ni(OH)₂during titration, has previously been reported. In this paper, the exact amount of glycerine and the complexing possibility of oxalate with nickel has been determined by means of conductivity titrations. This experimental work has been supported by the mathematical application of the Debye-Hu¨ckel and mass action equations as well as statistical analysis. The results were: (1) For determining boric acid in nickel plating solution, 20㎖ of 400㎖/ℓglycerine was sufficient, since 97% of the H₃BO₃was dissociated by this addition. (2) In the absence of Na₂C₂O₄, the continious precipitation of Ni(OH)₂a during titration with NaOH even past end-point for boric acid determination resulted in considerable analytical error. (3) In the presence of Na₂C₂O₄during titration, Ni^(++) combined with C₂O₄^(--) to form NiC₂O₄. The solution with this precititate of very fine, colloidal, transparent particles, remained quite clear for approximately 2 hours. Therefore it was shown that the presence of Na₂C₂O₄prevents the formation of gross Ni(OH)₂ precipitation by forming NiC₂O₄instead of a complex salt with Ni^(++), which did not interfere with the visible determination of the end-point for boric acid with NaOH titation. This observation may be interpreted in the light of the previously published solubility ratio for NiC₂O₄and Ni(OH)₂: 0.3㎎/100g H₂O (25℃), and 1.3㎎/100g H₂O (25℃), respectively. Precipitation of the less soluble, albeit transparent salt, NiC₂O₄, precluded therefore the precipitation of the Ni(OH)₂salt. |
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