Oxidation state, of oxygen

In H2O2 the oxidation state of oxygen is —1, intermediate between the values for O2 and H2O, and, as indicated by the reduction potentials on p. 628, aqueous solutions of H2O2 should spontaneously disproportionate. For the pure... 

A different aspect of AES concerns shifts in the observed peak energies that are due to chemical shifts of atomic core levels. Thus one is able to distinguish between atoms in different chemical environments (in a way analogous to XPS). In particular, studies of different oxidation states of oxygen adsorbed on metals have shown chemical shifts that grow with increasing oxygen valency. 

In essentially covalent compounds the oxidation state concept can be useful in their classification. The two main oxides of sulfur are S02 and SO3 and, if the oxidation state of oxygen is taken to be —2 by convention,... 

The oxidation state of oxygen is — 2, which gives a total of 14. In order to balance this with two manganese atoms, the oxidation state on each must be +7. 

Note that the oxidation state of oxygen in 02 is 0 because it is in elemental form. In this reaction there are no ionic compounds, but we can still describe the process in terms of a transfer of electrons. Note that carbon undergoes a change in oxidation state from -4 in CH4 to +4 in C02. Such a change can be accounted for by a loss of eight electrons (the symbol e stands for an electron) ... 

Note that the oxidation state of carbon changes from —2 to +4, an increase of 6. On the other hand, the oxidation state of oxygen changes from 0 to —2, a decrease of 2. This means that three oxygen atoms are needed to balance the increase in the oxidation state of the single carbon atom. We can write this relationship as follows ... 

It is quite clear that conversion between the fully oxidized and fully reduced forms of cytochrome oxidase is a four electron process126). In accord with the four electron accepting role of dioxygen, the titration of reduced oxidase with 02 (obtained in situ from /r-peroxo-bis (pentamine cobalt(II) tetranitrate) indicated complete oxidation of one reductant molecule by each molecule of 02127). There is no evidence for the liberation of intermediate oxidation states of oxygen such as peroxide or superoxide. The presence of two hemes and two coppers has lead to the assumption (but not without some strong exception, vide infra) that all four metal ions are involved in the red-ox process. 

The 0-0 bond in hydrogen peroxide is very weak. The oxidation state of oxygen in hydrogen peroxide is -1. 

Distinguish among normal oxides, peroxides, and superoxides. What is the oxidation state of oxygen in each case ... 

The oxidation state for hydride is always +l (H ) and the oxidation state for oxide is always -2 (0 ). However there are exceptions. For example the oxidation state of oxygen in hydrogen peroxide (H2O2) is -1 and in lithium hydride (LiH) the oxidation state of hydrogen is -1 . 

Emerson and Arnold also showed that eight excitations (photons) are necessary for each oxygen molecule produced. This is consistent with the fact that two electrons are necessary to raise the oxidation state of oxygen from -2 (as in H2O) to zero (as in Oj). There are two oxygen atoms per oxygen molecule and there are two photosystems to be passed by the electron, thus 2x2x2 excitations are necessary to produce one O2 molecule. 

Q Explain why the oxidation state of oxygen in the oxide ion is taken to be -2. 

A In fully ionic oxides the oxygen species present is 0 therefore the oxidation state of the oxygen is equal to the charge, i.e. -2. This value is taken to be the oxidation state of oxygen in compounds that are not necessarily ionic. 

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