Latimer and Volt-equivalent Frost Diagrams

There are two main methods of summarizing the thermodynamic stabilities of the oxidation states of elements in aqueous solution, known after their inventors. Latimer and Frost diagrams are usually restricted to the two extremes of standard hydrogen ion (pH = 0) or hydroxide ion (pH = 14) solutions. 

Latimer diagrams were invented by W. M. Latimer and consist of lines of text of the various oxidation states of an element arranged in descending order from left to right, with the appropriate standard reduction potentials (in volts) placed between each pair of states. The diagram for chromium in acid solution is written as  

For conciseness in the remainder of the chapter, the Latimer diagrams are presented with the relevant reduction potentials between the two oxidation states of the couple, as shown below, or in tabular form. 

The more exact forms of the aqueous cations, with their primary hydration shells, are normally omitted from the diagrams. As is the case with Crvl, which in acid solution exists as the dichromate ion, Cr2072-, the forms of any oxo anions are indicated by their formulae in the diagrams. The diagram for chromium summarizes the following important properties  

Q Construct a fully balanced equation lor the oxidation of Cm by molecular oxygen, and calculate the standard potential for the 

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This chapter is not concerned with the thermodynamic stability of ions with respect to their formation. Rather, it is concerned with whether or not a given ion is capable of existing in aqueous solution without reacting with the solvent. Hydrolysis reactions of ions are dealt with in Chapter 3. The only reactions discussed in this section are those in which either water is oxidized to dioxygen or reduced to dihydrogen. The Nernst equation is introduced and used to outline the criteria of ionic stability. The bases of construction and interpretation of Latimer and volt-equivalent (Frost) diagrams are described. 

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