Hydrogen peroxide as a reducing agent

As the above redox potentials indicate, only in the presence of very powerful oxidising agents does hydrogen peroxide behave as a reducing agent. For example ... 

Hydrazine hydrate is used as a reducing agent in synthetic and analytical reactions and as a solvent for many inorganic compounds. It also is used with methanol as a propellant for rocket engines. Another apphcation is catalytic decomposition of hydrogen peroxide. 

Hydrogen peroxide can function as a reducing agent with respect to Mn(III,IV), but the chemistry doesn t necessarily stop with reduction. Mn02 can bring about the disproportionation of H202, as shown in eqs 3 and 4. 

Write the half-reactions that show how hydrogen peroxide can function as an oxidizing and as a reducing agent in both acidic and basic solutions. Give the appropriate standard potentials for these halfreactions. 

When hydrogen peroxide acts as a reducing agent, oxygen is oxidized from the —1 oxidation state in H2O2 to the 0 oxidation state in O2. A typical example is the reaction of hydrogen peroxide with permanganate ion in acidic solution ... 

Vitamin C (ascorbate) (Fig. 9.5) has the ability to act as a reducing agent, i.e. it will tend to reduce more reactive species. This ability to reduce Fe3+ to Fe2+may be important in promoting iron uptake in the gut. Oxidation of ascorbate by reaction with reactive oxygen species or reactive nitrogen species seems to lead to its depletion. In vitro, vitamin C can also exert pro-oxidant properties. Fe3+ can react with ascorbate to form Fe2+ and the semi-dehydroascorbate or ascorbyl radical. The latter can react with hydrogen peroxide to form Fe3+, the hydroxyl radical and a hydroxide anion. A key question with regard to the pro- or anti- oxidant effects of ascorbate may therefore be the availability of transition metal ions. Neurons main-... 

As a reducing agent, hydrogen peroxide releases 2 electrons and oxygen gas is formed ... 

Even though it is commonly regarded as an oxidant, hydrogen peroxide can also be used as a reducing agent for powerful oxidants as in the recovery of spent catalysts. 

Explain why hydrogen peroxide can act sometimes as an oxidizing agent and sometimes as a reducing agent. 

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