Question

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The Zn-S-O-H20 Eh-pH diagram and the hydroxide precipitation diagram shown below from the literature is useful in predicting leaching and precipitation reactions of sulfides and oxides/hydroxides. Answer the following questions relevant to these diagrams (a) Write the balanced chemical equations relevant to zinc leaching in solutions represented by lines 4, 5, 18 and 19 (b) Calculate the theoretical pH of a solution of 12 mol/L NaOH at 25 °C, assuming unit activity coefficients (H2O=H*+OH;; K = 1014 at 25 °C). (c) Predict whether you can you use the solution in part (b) to leach ZnO: If the answer is "Yes" what is the product? Write a balanced equation for the chemical reaction. (i) If the Answer is "No" explain why. (ii) (d) Would you expect the pH to be as high as 16 (or above) at 25 °C as indicated in the diagram? Give reasons for your answer. (e) The electrolyte solution in a zinc plant has a composition of 1 mol/L zinc(II), 1 mol/L magnesium(II), and 1 mol/L sulfuric acid. It has a flow rate of 0.7 m/h. Use the solubility diagram of hydroxides at 25 C to estimate the rate of addition of lime ((Ca(OH)2, th) to precipitate zinc ions as Zn(OH)2 at pH 7 (Ca 40, O0= 16, H= 1) ZnS-H20 System Gons IM, H2S I atm) 0.5 10 Zn2 2 NSO n2 ZnO(a) 19 20 so Zn2 18 Zno H20 22 H2S(9) -0.5 so 12 ZnS(s) 1 13 15 24 Zno Zn(s) 16 17 H2S() H2 Znle) HS (aq) Zn(a) s2- -2.0 10 12 14 16 16 20 Zn-S-O-H2o Eh-pH diagram at 25 °C (A) Potential En(V) Zn2 Mg 10 11 12 13 14 pH (B) Solubility diagram for metal hydroxides at 25 °C uou, Lwl)60

Answer 1

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herusontal ne tn Peubai diagam indtakaj teadon tnvoling lectro bu inde HroH PaticPetu Pendent of p. Nesths, in this eactien 2+ S 2e Cs) Coa) NaoH - 12molL 12Mat 2c Canantiation o Nao Nat toh NaoH a ttong base 4twill be dbocated uaten Cempltedy (i) .-Therefere, Corentratlon Ot fsom dhociation of Na0H is 12M Cri) HTtOH Kw Cii) The afpos the dibocaton shifts the sauilebsium to loft ide (Accedng b lachateluri psunaple) 0m Noo of uat and Given that, kw 101at

PH- (4 - Po 87 bto,1 + hl = theerelical pH o the bolutien 81 bto Sl es, leaching of Naot bolutien hautng pH 15 07918 2mo Peible with line No S n the dlagam Predacti So it aletial ltne and the reactron is 2- Ca (aa))( ) Caai) Caa) Thus, the Paduct of suchyeactlon is