CHEM 281(01) SPRING 2003. Chapter 9. HOMEWORK 8.

1) Which of the following reactions are redox?

a) NaCl + AgNO₃ à AgCl + NaNO₃

b) NaOH + HCl    à NaCl + H₂O

c) Zn + 2HCl        à ZnCl₂ + H₂

d) 2Cr + 6HCl      à 2CrCl₃ + 3H₂

e) MnO₂ + 4HBr   àBr₂ + MnBr₂ + 2H₂O

2) Separate the reduction and oxidation half reactions in following chemical equations.

a) Zn + 2HCl à ZnCl₂ + H₂

b) MnO₂ + 4HBr à Br₂ + MnBr₂ + 2H₂O

c) 10K + 2KNO₃ à N₂ + 6K₂O

3) Balance following reactions that take place and give the sum of stoichiometric coefficients.

a) Cr₂O₇^2-(aq) + Cl^-(aq) ----- Cr³⁺(aq) + Cl₂(g) (acid solution)

b) Br^-(aq) + MnO₄(aq)    ----- Br₂(g) + Mn²⁺(aq) (acid solution)

c) Al(s) + MnO₄^-(aq)      ----- MnO₂(s) + Al(OH)₄^-(aq) (basic solution)

4) Construct a Galvanic cellemploying following reations:\

a) Ni(s) + Cu²⁺(aq) à Ni²⁺(aq) + Cu(s)

b) Zn(s) + 2H⁺(aq) à Zn²⁺(aq) + H₂(g)

5) Using the E⁰ values given in the table calculate the E^o_cell for reactions in problem 4 and identify following:

a) two half reactions; b) anode; c) cathode; d) direction of electron flow through the external wire.

6) Calculate the DG⁰ value for reactions in problem 4.

7) Using Ellingham diagram find out the minimum temperature required for the reduction of SiO₂ by C. Please write the redox reactions involved.

8) Estimate the potential difference required to reduce TiO₂ to metal at 1000⁰C.

9) Using Lattimer diagram(Appendix 2) calculate the E⁰ for the reduction of HClO₃ to HClO in aqueous acidic solution.