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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: jjc on July 01, 2008, 11:12:20 PM

Title: transition metals
Post by: jjc on July 01, 2008, 11:12:20 PM
hi I would like to ask why is there a difference between the following redox potentials?

[Fe(H2O)6]3+ + e-  <---> [Fe(H2O)6]2+
and
[Fe(CN)6]3- + e-  <---> [Fe(CN)6]4-

Thanks much
Title: Re: transition metals
Post by: macman104 on July 01, 2008, 11:18:42 PM
Read about Ligand Field Theory (http://en.wikipedia.org/wiki/Ligand_field_theory#High_and_low_spin_and_the_spectrochemical_series)
Title: Re: transition metals
Post by: vhpk on July 02, 2008, 12:13:41 AM
hi I would like to ask why is there a difference between the following redox potentials?

[Fe(H2O)6]3+ + e-  <---> [Fe(H2O)6]2+
and
[Fe(CN)6]3- + e-  <---> [Fe(CN)6]4-

Thanks much
CN- is a strong ligand and it stabilises Fe(III) w.r.t Fe(II) -> it makes [Fe(CN)6]3- more difficult to be reduced to Fe(II) compared to [Fe(H2O)6]3+. Hence, the E0 value of [Fe(CN)6]3- is lower
Title: Re: transition metals
Post by: jjc on July 02, 2008, 02:44:00 AM
thanks vhpk!