Latimer and Frost Diagrams

Latimer diagrams show successive reduction potmlials of half-reactions that connect various oxidation states of an elanent. Manganese is a good example since it occurs in a number of different oxidalion states from 0 (metal) to -e7 (permanganate) in aqueous solution MnO MnO (0.564) MnO - MnOJ (0.274) MnO Mn02 (4.27)  

FIGURE 10.4 Frost diagram for the oxidation states of manganese. 

Mn02- Mn + (0.95) Mn +Mn + (1.51) and Mn +- Mn (-1.18) (reduction potentials in V in parenthesis). The oxidized species appear on the left. If we are interested in the reduction potential when pmnanganate (MnOj) is reduced to Mn +, all the numbers are added and the sum is divided by the number of electrons, in the present case 5. 

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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. 

Example 2.12 involves the Latimer and Frost diagrams of Mn. Key data are summarized in Table 2.5. 

Latimer and Frost diagrams are different ways of representing the electrode potentials for different oxidation states of an element. Frost diagrams are useful for visual comparisons between elements, and for showing which species are likely to disproportionate. 

Latimer and Frost diagrams display the same information but in a different way. When interpreting electrode potential data, either in numerical or graphical form, it is important to remember that a single potential in isolation has no meaning,... 

The major use of hydrazine and its methyl derivatives is in rocket fuels. Hydrazine is a versatile reducing agent in acidic (as the protonated hydrazonium ion, N2Hs, see Latimer and Frost diagrams in Section 8.1.4) and basic solutions. 

Nitrogen exhibits rich redox chemistry in aqueous solution, as indicated by the Latimer and Frost diagrams in Section 8.1.4. 

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. 

Example 2.12 In the Latimer diagram for manganese in acidic medium, (a) find the values of E and Eg (see the table below), (b) draw the Frost diagram, and (c) find which is the most stable species of this system in acidic aqueous solution. The standard potential data are summarized in the table given above. 

T23.6 It would be a good idea (and practice as well) not only to compare the Latimer diagrams provided in the Resource Section 3, but also to construct one Frost diagram with data for both Np and Re to compare the two elements directly. Also note which oxidation states are missing for Re and Np and the chemical composition of the species for each oxidation state of the elements—this gives you a more complete idea of the differences between the two... 

Latimer diagrams (Appendix B.7) summarize many half-reactions. They also permit construction of Frost diagrams to illustrate the relative potency of species as oxidizing and reducing agents. For example, consider the Latimer diagram for nitrogen in acidic solution ... 

How is a Frost diagram useful The slopes of the lines connecting two species are proportional to AG° and —E for the half-reaction involving these species. One application is the determination of reduction potentials not directly provided in the Latimer diagram. For... 

Use the standard voltages in the Latimer diagrams for hydrogen in acidic and basic solutions to construct Frost diagrams. 

The redox potentials associated with this reaction are provided in the Latimer diagram for chlorine in basic solution (Appendix B.7) the Frost diagram for chlorine is in Figure 8.37. The disproportionation of CI2 to Cl and OCl in basic solntion is predicted by Figure 8.37, because CI2 is above the line between Cr and OCl . The free-energy... 

Use the Latimer diagrams for phosphorus in Appendix B.7 to construct Frost diagrams for acidic and basic conditions. Provide balanced reduction half-reactions for all adjacent couples in these Latimer diagrams. 

Figures 8.4b and 8.4c show potential diagrams for phosphorus and nitrogen in aqueous solution with [H ]= Imoldm , and these diagrams are the subject of worked example 8.8. We shall make more use of potential (Latimer) diagrams than Frost-Ebsworth diagrams in later chapters in this book, but the latter can readily be constructed from data...

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