Question CHem a LVl

• arigatoast

  3 Sep 09, 01:44

   

  With ref to the data booklet  predict and describe the observations when FeCl3 (aq) is added to the following cpds. In each case, cal the E node cell and write bal. eqns.

  i) Mn2 (SO4)3

  ii) CuI

   

  how am i suppose to know what will happen? help needed thanks!

   

• UltimaOnline

  3 Sep 09, 02:09

  List of Standard Redox Potentials : http://infinity.usanethosting.com/Tuition/StandardRedoxPotentials.gif Standard cell potential = standard reduction potential at cathode + standard oxidation potential at anode. If the cell potential is positive, redox reaction is feasible, current will flow (for galvanic/voltaic cells). Note that : Standard Reduction potential for Fe3+ to Fe2+ is + 0.77V Standard Oxidation potential for 2Cl- to Cl2 is - 1.36V Case 1 Standard Reduction potential for Mn3+ to Mn2+ is + 1.49V Standard Reduction potential for SO4 2- to SO2 is + 0.17V Standard Oxidation potential for 2SO4 2- to S2O8 2- is - 2.01V Conclusion : Under standard conditions, Redox reaction between Mn3+ and Cl- (to produce Mn2+ and Cl2) is feasible. Case 2 Standard Reduction potential for Cu+ to Cu is + 0.52V Standard Oxidation potential for Cu+ to Cu2+ is - 0.15V Standard Oxidation potential for 2I- to I2 is - 0.54V Conclusion : Under standard conditions, Redox reaction between Fe3+ and both Cu+ and I- (to produce Fe2+, Cu2+ and I2) is feasible. (Note : there are of course other species to consider as additional possible redox reactions, but unless the exam question specifies the redox potentials for such, otherwise based on the Data Booklet given in the exams, the above are the only directly relevant considerations).
• arigatoast

  3 Sep 09, 13:53

  Hi ultimaonline,

  thanks for yr reply. So for part II) i will have to write 2 eqns ? for the 2 possibilities?

• UltimaOnline

  3 Sep 09, 15:17

  Yes, write equations for whichever redox reactions are feasible, and calculate your standard cell potential based on these equations at cathode and anode.