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Ch.21 - Transition Elements and Coordination Chemistry
Chapter 21, Problem 3

What is the Lewis base in the reaction of oxalate with the mangenese ion to form [Mn(C2O4)3]2-? What is the oxidation state of Mn and the coordination number of the complex?  
(a) Lewis base is C2O42-; Mn oxidation number is +3; coordination number is 3.
(b) Lewis base is C2O42-; Mn oxidination number is +2; coordination number is 6.
(c) Lewis base is Mn2+; Mn oxidation number is +2; coordination number is 3.
(d) Lewis base is Mn4+; Mn oxidation number is +4; coordination number is 6.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Lewis Acids and Bases

In Lewis theory, a Lewis base is defined as a species that donates an electron pair to form a covalent bond, while a Lewis acid accepts an electron pair. In the reaction involving oxalate and the manganese ion, the oxalate ion (C2O4^2-) acts as the Lewis base by donating electron pairs to the manganese ion, facilitating the formation of the complex [Mn(C2O4)3]2-.
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Oxidation State

The oxidation state of an element in a compound indicates the degree of oxidation (loss of electrons) of that element. In the case of manganese in the complex [Mn(C2O4)3]2-, determining the oxidation state involves considering the charges of the ligands and the overall charge of the complex. The oxalate ion has a charge of -2, and with three oxalate ions, the total negative charge is -6, leading to an oxidation state of +3 for manganese.
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Coordination Number

The coordination number of a metal complex refers to the number of ligand atoms that are directly bonded to the central metal ion. In the complex [Mn(C2O4)3]2-, manganese is coordinated to three oxalate ligands, each of which binds through two oxygen atoms, resulting in a coordination number of 6. This reflects the total number of donor atoms surrounding the manganese ion.
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