Unformatted text preview: + 2 e → S – reduced (gains electrons) · Therefore, the format ion of calcium sulfide invo lves two halfreactions that occur simultaneously, one an oxidation and the other a reduction.
· Similarly, in the reaction of magnesium metal with hydrochloric acid Mg + 2 HCl → MgCl2 + H2 2
Mg → Mg + + 2 e oxidized (loses electrons) +
2 H + 2 e → H2 reduced (gains electrons) · In every oxidat ionreduction reaction, the number of electrons lost must be equal to the number of electrons gained. Examples: 1. Identify each of the reactions below as oxidat ion or reduction: 2
a) Zn → Zn + + 2 e ______________________ –
b) Cl2 + 2 e → 2 Cl ______________________ 3
c) Fe + + e → Fe + ______________________ –
d) 2 Br– → B2 + 2 e ______________________ 10 Chemistry 51 Chapter 6 OXIDATIONREDUCTION IN BIOLOGICAL SYSTEMS
· Many important bio logical reactions invo lve oxidation and reduct ion. In these reactions, oxidation invo lves addition of oxygen or loss of hydrogen, and reduction invo lves loss of oxygen or gain of hydrogen.
· For example, poisonous methyl alcoho l is metabolized by the body by the fo llo wing react ion: CH3OH → H2CO + 2 H· methyl alcohol formaldehyde oxidation (loss of hydrogen) · The formaldehyde is further oxidized to formic acid and finally carbon dio xide and water by the fo llowing reactions: 2 H2CO + O2 → 2 H2CO2 formaldehyde formic acid oxidation (gain of oxygen) 2 H2CO2 + O2 → CO2 + H2O formic acid oxidation (gain of oxygen) · In many biochemical oxidationreduct ion reactions, the transfer of hydrogen atoms produces energy in the cells. The oxidat ion of a typical biochemical mo lecule can invo lve the transfer of two hydrogen atoms to a proton acceptor such as coenzyme FAD to produce its reduced form FADH2. 11 Chemistry 51 Chapter 6 OXIDATIONREDUCTION IN BIOLOGICAL SYSTEMS
· In summary, the particular definit io n of oxidat ionreduction depends on the process that occurs in the reaction. A summary o f these definit io ns appears below: Examples: 1. Lino l...
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