The Stabilization of Oxidation States

Stannate(II) ions are powerful reducing agents. Since, for tin, the stability of oxidation state -b4 is greater than that of oxidation state -b2, tin(II) always has reducing properties, but these are greater in alkaline conditions than in acid (an example of the effect of pH on the redox potential, p. 101). 

For many years, the chemistry of silver and gold was believed to be more similar than is now known to be the case [1-10]. In the Cu-Ag-Au triad, the stability of oxidation states does not follow the usual trend of increasingly stable high oxidation state on descending the group for copper, the +2 state is the most important, for silver it is the +1 state and, though oxidation states between -1 and +7 are claimed, for gold it is the +1 and +3 states that dominate its chemistry. The types of compound are summarized in Table 4.1. 

The Stabilization of Oxidation States of the Transition Metals R. S. Nyholm and M. L. Tobe... 

As a more complex example, we examine the stability of oxidation states of aqueous sulfur as a function of pH. This exercise will bring out the treatment of thermodynamically unstable species and the change of sulfur speciation with pH. 

Other applications of emfs include the prediction of thermodynamically possible redox reactions [e.g., will Sn4+oxidize Fe2 to Fe3+ ] and the stabilization of oxidation states through the formation of complexes. The former is a straightforward application of thermodynamics and will not be discussed further here. The second is of great importance. It was introduced in Chapter 11 and will be discussed further below. 

Describe the trend in the stability of oxidation states moving down a group in the d block (for example, from chromium to molybdenum to tungsten). 

Jorgensen (71—73) has formulated an ingenious approach for predicting the stabilities of oxidation states, based on Eq. (3). If we consider one-electron changes only, Eq. (3) can be rewritten... 

If you are not thoroughly familiar with the principles of electrochemistry, you should review Chapter 10 and the Latimer diagram derived there (below) before considering the following discussion for determining the stability of oxidation states ... 

The stability of oxidation states of the heaviest elements, and the influence of relativistic effects, can be investigated by reduction experiments. For that purpose, knowledge of relative stabilities of oxidation states, redox potentials E°, is of crucial importance E° is needed to decide which reducing or oxidizing agent should be chosen to reach the desired state. 

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