Redox Reactions: Gain and Loss of Oxygen

Introduction

Redox reactions, short for reduction-oxidation reactions, are fundamental chemical processes that involve the transfer of electrons between chemical species. A key type of redox reaction involves the gain or loss of oxygen.

Oxidation

Oxidation is the process of losing electrons. In the context of oxygen, oxidation can be defined as the gain of oxygen atoms or the loss of electrons that results from the removal of oxygen. Oxidation states are used to track electron transfer.

Example: The reaction of sodium with oxygen.

$2Na(s) + O_2(g) \rightarrow 2NaO_2(s)$

In this reaction, sodium (Na) is oxidized because it gains an electron to become a sodium ion ($Na^+$). The oxidation state of Na changes from 0 to +1.

Reduction

Reduction is the process of gaining electrons. In the context of oxygen, reduction involves the loss of oxygen atoms or the gain of electrons that results from the addition of oxygen.

Example: The reaction of copper(II) ions with hydrogen.

$Cu^{2+}(aq) + 2e^- \rightarrow Cu(s)$

Here, copper(II) ions ($Cu^{2+}$) are reduced by gaining two electrons to form solid copper (Cu). The oxidation state of Cu changes from +2 to 0.

Identifying Redox Reactions Involving Oxygen

To identify redox reactions involving oxygen, look for the following:

• A change in the oxidation state of oxygen.
• The formation of oxides (compounds containing oxygen).
• Reactions where a substance gains oxygen or loses oxygen.

Examples of Redox Reactions Involving Oxygen

Here are some common examples of redox reactions involving oxygen:

1. Combustion: The rapid reaction between a substance with oxygen, producing heat and light. (e.g., burning fuels like methane, carbon, or wood)
2. Reaction of metals with oxygen: Formation of metal oxides (e.g., iron rusting, magnesium burning in air).
3. Displacement reactions: A more reactive metal displaces a less reactive metal from its oxide. (e.g., Zinc displacing copper from copper oxide)
4. Decomposition of hydrogen peroxide: Hydrogen peroxide decomposes into water and oxygen.

Oxidation States and Oxygen

The oxidation state of oxygen is usually -2 in most compounds. However, there are exceptions:

• In peroxides (e.g., $H_2O_2$), oxygen has an oxidation state of -1.
• In oxides of nonmetals (e.g., $CO_2$), oxygen has an oxidation state of +4.

Table Summarizing Redox Reactions Involving Oxygen

Reaction Type	Example	Oxidation	Reduction
Combustion	$CH_4(g) + 2O_2(g) \rightarrow CO_2(g) + 2H_2O(g)$	Carbon in methane gains oxygen	Oxygen in oxygen is lost
Reaction of Metals with Oxygen	$4Fe(s) + 3O_2(g) \rightarrow 2Fe_2O_3(s)$	Iron loses electrons to form $Fe^{3+}$	Oxygen gains electrons to form $O^{2-}$
Displacement Reaction	$Zn(s) + Cu(aq) \rightarrow ZnSO_4(aq) + Cu(s)$	Zinc loses electrons	Copper(II) ions gain electrons
Decomposition of Hydrogen Peroxide	$2H_2O_2(aq) \rightarrow 2H_2O(l) + O_2(g)$	Oxygen in hydrogen peroxide is lost	Oxygen in oxygen gains electrons