Main Difference – Reducing Agent vs Oxidizing Agent
Reducing agents and oxidizing agents are chemical compounds involved in redox reactions. These compounds are the reactants of a redox reaction. The main difference between reducing agent and oxidizing agent is that reducing agent can lose electrons and be oxidized whereas oxidizing agent can gain electrons and be reduced.
Key Areas Covered
1. What is a Reducing Agent
– Definition, Properties, Reaction Mechanisms, Examples
2. What is an Oxidizing Agent
– Definition, Properties, Reaction Mechanisms, Examples
3. What is the Difference Between Reducing Agent and Oxidizing Agent
– Comparison of Key Differences
Key Terms: Half Reaction, Oxidation, Oxidation State, Oxidizing Agent, Redox Reaction, Reducing Agent, Reduction
What is a Reducing Agent
A reducing agent is a substance that can be oxidized by losing some of its electrons. The loss of electrons causes the reducing agent to get a positive charge since the charge of an atom is dependent on the balancing of the positive charge of the nucleus by the negative charge of the electrons. Therefore, after losing electrons, there aren’t enough negative charges to balance the corresponding positive charge of the nucleus. Thus a positive charge is left. This charge is called the oxidation state of the atom.
A reducing agent can be a substance containing either the same element or different elements. In order to be a reducing agent, a compound that is composed of several elements should have at least one element that is in a lower possible oxidation state so that this element can oxidize into a higher oxidation state, losing its electrons. For example, SO32- can act as a reducing agent. The sulfur atom is in +4 oxidation state there. The highest oxidation number that sulfur can hold is +6. Therefore, the +4 state sulfur can be oxidized to the +6 oxidation state.
In redox reactions, the overall reaction is obtained from the half reactions that occur in that system. The two half reactions are the oxidizing reaction and the reduction reaction. The oxidizing reaction always represents the oxidation of the reducing agent.
In organic chemistry, Red-Al or reducing aluminum compound is a commonly used reducing agent. The following image shows the functional groups that are reduced by this compound.
Oxidation Reactions of Reducing Agents
Followings are the types of reactions reducing agents undergo.
Oxidation of Zero Oxidation State into Positive Oxidation State
Lithium (Li) is a strong reducing agent because it readily loses an electron obtaining a +1 oxidation state. The half reaction would be,
Li → Li+1 + e–
Oxidation of a Positive Oxidation State into a Higher Positive Oxidation State
H2C2O4 is also a good reducing agent. The oxidation state of the C atom is +3. The highest oxidation state that the C atom can have is +4. Therefore, can oxidize into CO2. The half reaction is,
H2C2O4 → 2CO2 + 2H+ + 2e–
Oxidation of a Negative Oxidation State into a Zero Oxidation State
O2 can be produced from O2- in oxides. For example, Ag2O can be oxidized into Ag and O2.
2Ag2O → 4Ag + O2
Oxidation of a Negative Oxidation State into a Positive Oxidation State
Oxidation of H2S into H2SO4 cause the oxidation number of sulfur to change from -2 to +6.
S2- + 4H2O → SO42- + 8H+ + 8e–
What is an Oxidizing Agent
An oxidizing agent is a substance that can be reduced by obtaining electrons. Therefore it is called an electron receiver or acceptor in redox reactions. The half reaction of reduction is the reaction that the oxidizing agents undergo. When electrons are obtained from outside, there are more negative charges that cannot be completely neutralized by the nucleus. Therefore, the atom obtains a negative charge. But if this reduction occurs in a positively charged atom, it can obtain a lower positive charge or a neutral charge.
In oxidizing agents, the reduction causes the oxidation state of the atom to get decreased. For example, if there’s an atom having a positive charge (such as Na+), it can be reduced to zero oxidation state (Na+ into Na). Similarly, an atom or molecule having a zero charge (such as O2) can be reduced to a negative charge (O2 into 2O2-).
Reduction Reactions of Oxidizing Agents
Reduction of oxidizing agents can occur mainly in following ways.
Reduction of Zero Oxidation State to a Negative Oxidation State
Oxygen (O2) and ozone (O3) can act as oxidizing agents. They reduce into O2-. This reduced form can be included in different forms such as O2- in H2O and CO2.
O2 + 4H+ + 4e– → 2H2O
Reduction of Positive Oxidation into a Lower Positive Oxidation State
Manganese (Mn) of MnO4– can be reduced into Mn+2 or MnO2 (Mn+4).
MnO4– + 8H+ + 5e– → Mn+2 + 4H2O
Reduction of Positive Oxidation State to a Zero Oxidation State
HF (-1 oxidation state of F) can be reduced into F2 (zero oxidation state of F).
2 HF → F2 + H2
2F– → F2 + 2e–
Reduction of a Positive Oxidation State into Negative Oxidation State
Sulfur in SO4-2 (+6 oxidation state) can be reduced into H2S (-2 oxidation state).
SO42- + 8H+ + 8e– → S2- + 4H2O
Difference Between Reducing Agent and Oxidizing Agent
Reducing Agent: A reducing agent is a substance that can be oxidized by losing some of its electrons.
Oxidizing Agent: An oxidizing agent is a substance that can be reduced by obtaining electrons.
Reducing Agent: The oxidation state of reducing agent increases.
Oxidizing Agent: The oxidation state of oxidizing agent decreases.
Reducing Agent: Reducing agent acts as the electron donor.
Oxidizing Agent: Oxidizing agent acts as the electron receiver.
Change of Oxidation State in the Agent
Reducing Agent: Reducing agent is oxidized during the reaction.
Oxidizing Agent: Oxidizing agent is reduced during the reaction.
Change of Oxidation State in the Other Reactants
Reducing Agent: Reducing agent causes the reduction of another reactant.
Oxidizing Agent: Oxidizing agent causes the oxidation of another reactant.
Reducing agents and oxidizing agents are chemical compounds involved in redox reactions. The main difference between reducing agent and oxidizing agent is that reducing agent can lose electrons and be oxidized whereas oxidizing agent can gain electrons and be reduced.
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