Oxidation and Reduction
Text 31 A Oxidation and Reduction - раздел Образование, Part One THE PREDICATE Generally Speaking, The Simple Meanings Of These Terms Arc That Oxidation Is ...
Generally speaking, the simple meanings of these terms arc that oxidation is the addition of oxygen to a substancc and reduction is the
removal of oxygen. Needless to say, hydrogen seems to be the chemical opposite of oxygen (the two elements combine readily, and arc evolved at opposite clcctrodes during electrolysis). Removal of hydrogen is, therefore, similar to the addition of oxygen, and addition of hydrogen is similar to the removal of oxygen. Fuller meanings of the two terms arc therefore: Oxidation is the addition of oxygen to, or removal of hydrogen from, a substancc. Reduction is the removal of oxygen from, or addition of hydrogen to, a substancc.
2S02 + 02« 2SOj (oxidation of S02; addition of oxygen)
PbO + H2 — Pb + H20 (reduction of PbO; removal of oxygen)
Cl2 + H2 — 2HC1 (reduction of Cl2; addition of hydrogen)
H2S + Cl2 — Si + 2HC1 (oxidation of H2S; removal of hydrogen)
The terms now arc applied to reactions in which neither oxygen nor hydrogen arc involved. To take an example, the changc of ferrous oxide to ferric oxide is, obviously, an oxidation; similarly, we can regard the changc of any ferrous compound to a fcrric compound as an oxidation (and a changc of fcrric to ferrous as a reduction): 4FcO + 02 —1> 2Fc20j; FeCl2 + Cl2 — 2FeClj. Note that the valency of the metal increases during oxidation.
Metals and hydrogen form positive ions (e. g., Na* and H*) and arc, therefore, callcd clcctropositivc. Non-metals and acid radicals arc electronegative as they form negative ions (c. g., 0:", SOr")- Putting it another way, more complete definitions of the two terms arc:
Oxidation is the addition of any clcctroncgativc clement or radical to, or removal of any clcctropositivc clement or radical from, a substancc. Reduction is the opposite.
An oxidizing agent is a substance which brings about oxidation, a reducing agent is a substancc which brings about reduction.
Oxidizing agents include: oxygen, hydrogen peroxide, nitric acid, sulphuric acid, chlorinc, potassium permanganate, potassium dichromate.
Reducing agents include: hydrogen, carbon, carbon monoxide, sulphur dioxide, hydrogen sulphide, ammonia, and most metals and non-metals. The equations for the oxidation of ferrous chloride arc:
2FcCl2 + CI2-2FcCb; ionically: 2F<r* + Cl2 — 2Fe3' + 2C1".
As already mentioned, the oxidation involves a changc of ferrous ion to ferric, it occurs by loss of an electron (c). And oxidation of chlorine to ehloride ions takes placc by gain of electrons:
pc> _ e — FeJ* (oxidation);
Cl2 + 2e — 2C1- (reduction).
To summarize, oxidation is the removal of electrons from a substancc. Reduction is the addition of electrons to a substancc.
An oxidizing agent is a substancc that accepts electrons. A reducing agent is a substancc that supplies electrons.
(Remember the word ORE — Oxidation is Removal of Electrons.)
