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Oxidation Definition
Oxidation is the loss of electrons during a reaction by a molecule, atom or ion.
Oxidation occurs when the oxidation state of a molecule, atom or ion is increased. The opposite process is called reduction, which occurs when there is a gain of electrons or the oxidation state of an atom, molecule, or ion decreases.
H2 + F2 → 2 HF
In this reaction, hydrogen is being oxidized and fluorine is being reduced. The reaction may be better understood if it is written in terms of two half-reactions.
H2 → 2 H+ + 2 e–
F2 + 2 e– → 2 F–
Note there is no oxygen anywhere in this reaction!
Historical Definition of Oxidation Involving Oxygen
An older meaning of oxidation was when oxygen was added to a compound. This was because oxygen gas (O2) was the first known oxidizing agent.
While the addition of oxygen to a compound typically meets the criteria of electron loss and an increase in the oxidation state, the definition of oxidation was expanded to include other types of chemical reactions.
A classic example of the old definition of oxidation is when iron combines with oxygen to form iron oxide or rust. The iron is said to have oxidized into rust. The chemical reaction is:
2 Fe + O2 → Fe2O3
The iron metal is oxidized to form the iron oxide known as rust.
Electrochemical reactions are great examples of oxidation reactions. When a copper wire is placed into a solution that contains silver ions, electrons are transferred from the copper metal to the silver ions. The copper metal is oxidized. Silver metal whiskers grow onto the copper wire, while copper ions are released into the solution.
Cu(s) + 2 Ag+(aq) → Cu2+(aq) + 2 Ag(s)
Another example of oxidation where an element combines with oxygen is the reaction between magnesium metal and oxygen to form magnesium oxide. Many metals oxidize, so it’s useful to recognize the form of the equation:
2 Mg (s) + O2 (g) → 2 MgO (s)
Oxidation and Reduction Occur Together (Redox Reactions)
2 Mg + O2 → 2 [Mg2+][O2-]
comprised of the following half-reactions:
Mg → Mg2+ + 2 e–
O2 + 4 e– → 2 O2-
Historical Definition of Oxidation Involving Hydrogen
For example, according to this definition, when ethanol is oxidized into ethanal:
CH3CH2OH → CH3CHO
Ethanol is considered oxidized because it loses hydrogen. Reversing the equation, ethanal can be reduced by adding hydrogen to it to form ethanol.
Using OIL RIG to Remember Oxidation and Reduction
So, remember the modern definition of oxidation and reduction concern electrons (not oxygen or hydrogen). One way to remember which species is oxidized and which is reduced is to use OIL RIG. OIL RIG stands for Oxidation Is Loss, Reduction Is Gain.
Oxidation Key Takeaways
Oxidation occurs when an atom, molecule, or ion loses one or more electrons in a chemical reaction.
When oxidation occurs, the oxidation state of the chemical species increases.
Oxidation doesn’t necessarily involve oxygen! Originally, the term was used when oxygen caused electron loss in a reaction. The modern definition is more general.
Introduction to Oxidation Reduction (Redox) Reactions
ASSIGNMENT : OXIDATION ASSIGNMENT MARKS : 10 DURATION : 1 week, 3 days