Examine the procedure in Table 7-1 for the Fajans titration of Zn2+.Zn²⁺. Do you expect the charge on the precipitate to be positive or negative after the equivalence point?

Table 7-1

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TABLE 7-1 Applications of precipitation titrations Species analyzed Br-, I-, SCN-, CNO-, AsO43-, Br, I, SCN, CNO, ASO, CI, PO43-, CN, C2042-, CO32-, S2-, CrO42- CI, PO, CN, C₂0, cos, Cro BH4 BH Cl, Br, I-, SCN-, Fe(CN)64- Cl, Br, I, SCN, Fe(CN) Zn2+Zn²+ SO42- SO² Hg₂+ Hg22+1 PO43-, C2042-PO, C₂0² Notes Volhard Method Precipitate removal unnecessary Precipitate removal required Back titration of Ag+Ag left after reaction with BH4 BH4 18Ag8OH-8Ag(s)+H2B03- BH BH₂ + 8Ag +80H 8Ag(s) + H₂BO3 + 5H₂O +5H201 Fajans Method Titration with Ag+, Ag. Detection with dyes such as fluorescein, dichlorofluorescein, eosin, bromophenol blue to produce K2Zn3[Fe(CN)612. K₂ Zns [Fe(CN)6]2. Ba(OH)2 in 50 vol%50 vol% aqueous methanol using alizarin red Sas K4Fe(CN)6 Titration with K4Fe(CN)6 End-point detection with diphenylamine Titration with Ba(OH)2 indicator Titration with NaciNaCl to produce Hg2012. HgCl₂ End point detected with bromophenol blue Pb(CH3CO2)2 to give Pb3(PO4)2 Titration with Pb(CH3CO2)2 PbC204 End point detected with dibromofluorescein (PO43-) (C2042-) (C₂0) Pb3(PO4)2 or PbC204. (PO), or fluorescein