CHM096 Tutorial 6 Electrochemistry

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CHM 096 TUTORIAL 6 Mar 2013 (ELECTROCHEMISTRY)

1. Determine the oxidation number of the first name element in the following ions.
a) Cr2O72 d) AsO33
b) SbF6 e) BaH2
c) MoO42 f) ClO4−
2. Determine whether each of the reactants shown in the following half-reactions is being oxidized or reduced. a) As4+  As3+ b) Cl2O7  HClO4 c) C2H4O  C2H6O d) SO2  SO42− e) Cr2O72−  Cr3+
3. Indicate whether each of the following is or is not a redox reaction. a) CaCl2 + 2NaF  CaF2 + NaCl b) CaI2 + Cl2  CaCl2 + I2 c) PbO2 + 4HCl  PbCl2 + Cl2 + 2H2O d) FeS + 2H+  Fe2+ + H2S
4. State whether SO2 acts as an oxidising agent or as a reducing agent in each of the following redox reactions. a) SO2 + Mg  2MgO + S b) 3SO2 + Cr2O72− + 2H+  3SO42− + 2Cr3+ + H2O c) SO2 + 2NO3−  SO42− + 2NO2 d) SO2 + 2H2S  3S + 2H2O
5. Write the balanced ionic half-equation to show: a) the oxidation of iodine (I2), in acid medium, to give iodate ion (IO3−) b) the reduction of vanadyl ion (VO2+) to give vanadium (III) ion, in acid medium. c) the reduction of manganese dioxide, in acid solution, to give manganese (II) ion.

6. When copper metal is placed in concentrated nitric acid, the solution turns green and brown coloured NO2 gas evolved. Cu(s) + 4HNO3(aq)  Cu(NO3)2(aq) + 2NO2(g) + 2H2O(l)
a) Which element is reduced?
b) Which element is oxidised?
c) Which is the oxidising agent?
d) Which is the reducing agent?

7. When metallic zinc is added to an aqueous solution of silver nitrate, zinc dissolves and silver is deposited.

a) Write a balanced molecular equation for the reaction.
b) Write the ionic half-equations for the oxidation and reduction reactions.

8. Use the redox half-reaction method to write a balanced net ionic equation for each of the following reactions occurring in acidic solutions.
a) Sn2+ + CrO4−  Sn4+ + Cr3+
b)

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