Calamine, which is used for the relief of skin bums and irritation, is a mixture

Question

Calamine, which is used for the relief of skin bums and irritation, is a mixture of ZnO, Fe_2O_3 and other ingredients. A 1.022 gram sample of calamine is dissolved in aqueous acid and diluted to the mark in a 250 mL Class A volumetric flask. Aqueous KF is added to form a very stable fluoride complex with F3^3+ (aq) that is non-reactive with EDTA; under these conditions, when suitably buffered. Zn^2+ (aq) is titrated quantitatively with EDTA. A 10.00 mL aliquot of the fluoride-treated calamine solution is titrated with Y solution, requiring 38.78 mL of 0.01294 M Y to titrate the Zn. A second 50.00 mL aliquot is used to determine Fe. This is done via a displacement titration under these conditions. Fe^3+ (aq) reacts quantitatively with ZnY^2-. Under these conditions, the Fe consumes 2.40 mL of a 0.002727 M EDTA solution. Write a balanced net ionic equation for the reaction representing the displacement titration of Fe^3+(aq) reacts quantitatively with ZnY^2-.

Explanation / Answer

In an EDTA displacement titration, an unmeasured excess of a solution containing the zinc complex of EDTA is introduced into the solution of an analyte that forms a more stable complex that of zin

Fe3+(aq) + ZnY2-(aq) FeY1-(aq) + Zn2+(aq)

In this reaction Fe3+displaces Zn2+ from ZnY2- and form a more stable complex FeY1-

Balanced net ionic equation-

Fe3+ +3e ----> Fe

Y4- -------> Y1- + 3e

Balanced net – Fe3+ + Y4- --------->FeY1-

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