Oxidation-Reduction Reactions

Oxidation-Reduction reaction is also called redox reaction, which involves transfer of electrons between two species.  The oxidation number of atoms or ions change by either gaining or losing electron. Oxidation-reduction are so vital that it occurs in the different processes from our environment, plants and animals. Example of which is  the reaction of Magnesium and oxygen

2Mg(s)   +   O₂(g)    à    2MgO(s)

The example above involves the reaction of magnesium atom with the oxygen atom producing magnesium oxide. Magnesium oxide is made up of  Mg⁺² ion and O^-2 ion.  We have to analyze what happens to magnesium and oxygen in the reaction by trying to identify if they undergo oxidation or reduction.

             2Mg    à     2 Mg⁺²     +     4e^-

O₂    +    4e^‑    à     2O^-2

The above equations are the two half-reactions that occur in the reaction of magnesium and oxygen. Half-reaction shows the electrons involved in a redox reaction..  Two magnesium atoms gives up 4 electrons to oxygen atoms and oxygen atoms gain 4 electrons from magnesium atom. The sum of the two half-reactions give the overall reaction which is

2Mg   +   O₂   +  4e^-     à     2Mg⁺²     +     2O^-2     +    4e^-     

If we cancel electrons on both sides of the equations, it will look like this:

2Mg    +     O₂      à     2Mg⁺²     +     2O^-2

Checking the equation if balance, Mg has 2 atoms, O has also 2 atoms and both charges are equal to zero in the reactant side and in the product side.

Understanding about the two half-reactions, oxidation reaction, refers to the half-reaction that involves the loss of electron while a reduction reaction refers to the half-reaction that involves the gain of electrons.  In the above reaction, Mg is oxidized and O is reduced.  Mg is called the reducing agent, since it is the one responsible for the O to be reduced.  On the other hand O is the oxidizing agent since it is the one responsible for the Mg to be oxidized.  Therefore, reducing agent is the substance that donates electrons and is oxidized while oxidizing agent is the substance that accepts electrons and is reduced.

TRY THIS PROBLEM:

Write the half-reaction and identify the reducing and oxidizing agent of the following redox reaction:

1.       4Fe  +   3O₂     à      2Fe₂O₃

2.        Cl₂    +    2NaBr     à    2NaCl   +   Br₂ 

1.    3.        Si   +   2F₂     à    SiF₄

1.    4.        H₂   +   Cl₂    à    2HCl