Abstract

CHAVEZ-RAMOS, Kenia  and  BONILLA-MARTINEZ, Dalia. Influence of acidity in the precipitation process on Mohr's method. Educ. quím [online]. 2014, vol.25, n.4, pp.440-445. ISSN 0187-893X.

The main goal of this study was to demonstrate the importance of acidity on precipitation process of Ag₂CrO₄ and Ag₂O, which can be formed in Mohr's method. This can be explained through the interpretation of a Predominance-Existence Diagram, which shows reliable results of a didactic experiment. The first part of this study consists of identifying two kinds of solids, Ag₂CrO₄, which is reddish, and Ag₂O brownish. The second part shows that acidity affects in speciation of Cr (VI) by changes in the color of the aqueous solution. Finally, it has been demonstrated that pH affects on absence or formation of certain solids. These changes can be explained by a predominance-existence diagram, which is useful to identify a logarithmic curve related with conditional solubility of Ag₂CrO₄ or Ag₂O, the conditional solubility constant, and also concentration of silver at saturation. The finding of minimum solubility-without Ag₂O can be formed-justifies that optimal interval pH to titrate on Mohr's method is 7.0 <pH< 10.

Keywords : Mohr's method; silver (I) oxide; silver (I) chromate; conditional solubility; conditional solubility constant.

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