Reducing agent relative strengths

Use standard potentials (Table 18.1) torn compare the relative strengths of ditferent oxidizing agents different reducing agents. (Example 18.2 Problems 9-18) 9,10,16,18... 

Predict the relative strengths of several metals as reducing agents. 

Read the entire laboratory activity. Form a hypothesis about the relative strengths of these four metals as reducing agents, from strongest to weakest. Record your hypothesis on page 154. 

From the E° values, we see that the relative strengths of reducing agents are Li > K > Ca. It is expected that for the reactions of these metals with water, AH xn for Li would be more negative than AH xn for K, which is in turn more negative than Afor Ca. This trend is true only for Li and K. AEfxn for Ca is much more negative than predicted since it is a 2A metal (Li and K are 1A metals) and reacts with twice as much water to produce twice as much H2 gas. 

Lacking a table of standard electrode potentials, or one that is adequate, what guidelines can be used to identify oxidizing and reducing agents, and to estimate their relative strengths Here are a few. 

The formation of alcohols by the reduction of aldehydes and ketones, carboxylic acids, esters and epoxides is summarized in Scheme 2.9. The change in the strength of the reducing agents, from the relatively mild sodium borohydride to the vigorous lithium aluminium hydride, reflects the difference in the electron deficiency of the carbonyl group which is being reduced. 

Going down th motal column, any metal will replace any metal below it in solution. Relative strength of the metals as reducing agents (electron donors) decreases down the table... 

Table of relative strengths of oxidizing and reducing agents (see table on the following page)... 

FIGURE 4.4 Relative strength of oxidant (oxidizing agent or electron acceptor) and reductant (reducing agent or electron donor). 

The electron transfer producing free radicals as shown above is preceded by the formation of unstable coordination complexes of the metal ions with alkyl hydroperoxides. The relative importance of Reaction 1.76 and Reaction 1.77 depends upon the relative strength of the metal ion as an oxidizing or reducing agent. When the metal ion has two valence states of comparable stability, both Reaction 1.76 and Reaction 1.77 will occur, and a trace amount of the metal can convert a large amount of peroxide to free radicals according to the sum of the two reactions (Reaction 1.78). This is true of compounds of metals such as Fe, Co, Mn, Cu, Ce, and V, commonly called transition metals. 

Look up the standard reduction potentials for sodium, magnesium, and aluminum. What do these potentials indicate in terms of their relative strengths as reducing agents Should aluminum liberate hydrogen readily from water Indicate clearly your reasoning. 

Figure 20.11 Relative strengths of oxidizing and reducing agents. 

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