In the early 17th century when the scientists started to recognize and begun to research about the chemical reaction, one of the very first theories that drew their attention was this oxidation and reduction theory. The combustion of woods and rusting metal reaction was the one which interested them to take this chemistry to another level of understanding. But the question is what is this oxidation and reduction theory about? Here the explanation about the theory that you should know before entering the chemistry world.
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1. Oxidation and Reduction Theory
What is Difference between Oxidation and Reduction? The first substance that scientists found was air. It was right before 18th century that scientists first found that air was not an element but actually a substances neglected the theory once found by Aristotle. Created by combining oxygen and another substances made scientists at those time questioning themselves about this new reaction. They were try to make an experiment to separate oxygen from combustible substances. Many scientists tried to figure out the role of oxygen in combustion phenomenon.
Indeed, here is the Difference between Reduction Oxidation. The first theory was brought by Georg Ernst Stahl, but it still has flaws like why the residue of the combustion process was heavier than before when it still a metal. The ones who finally able to figured out and stated bravely the role of oxygen in combustion was Lavoiseur. He gave an accurate calculation that no one even can imagined it. He mentioned that the quantity of the gases was important in order to understand the chemical reaction in combustion. The example for oxidation and reduction reaction in daily life is fire, rusting metals, combustion of woods, browning of fruits, respiration, and photosynthesis.
Atoms always consists only with positive atom while surrounding by negative atoms, forming a compunds from two or more elements need one element which should donate atom while the other element should accept the transferring atoms. This oxidation and reduction theory is about the transferring reaction from one atom to other atom. Its often called as redox theory, short for reduction and oxidation. Redox theory basically talking about the gaining and reducing of electron(s) from one atom to another atom.
The concept of this theory is actually about one substances gaining more electron(s) while the other ones lose the same amount of electrons. It means that this reaction must be happened at the same time, there is no oxidation without reduction, they just like two sides that can not be separated. The concept is similar to those acid-base relationship. The differences between redox and acid-base is which in redox reaction the number of electron(s) will change while in acid-base reaction the number of electron(s) will still the same in the end. For further explanations, here are the formula and compounds to know Difference between Reduction Oxidation.
Differences between Oxidation and Reduction
2Zn(s) + O2 (g) –> 2ZnO(s)
The half oxidation reaction is
2zn –> 2Zn2+ + 4e–
The half reduction reaction is
O2 + 4e– –> 2O2-
In above equation, zinc is the element that losing its electrons, causing the other which means oxygen to gain electrons or be oxidized. Zinc called by the oxidizing agent or oxidant because its causing the oxidation to other element. In other hands oxygen is the one which gain electrons or be oxidized. Oxygen is called by reducing agent or reductant, because its cause the other elements be reduced.
The one which contain an element that is oxidized always the reducing agent, while the one which always contain an element that is reduced always the oxidizing agent. A substance can be an oxidant and reductant as well as long as they have a capability to accept or give electron easily.
In the sodium chloride reaction, sodium act as a reducing agent and chlorine as oxidizing agent. It happens because sodium make it easier for chlorine to be reduced, means sodium is oxidized, while for chlorine, it make sodium easier to be oxidized, so chlorine reduced.
[tab title=”The Formula
2Na(s) + Cl2(g) –> 2NaCl(s)
Half reaction of oxidation: 2Na(s) à 2Na + 2e–
Half reaction of reduction: Cl2(g) + 2e– –> 2Cl–
Here another examples for oxidation and reduction reaction:
I2(aq) + 2e– –> 2I– (aq)
Br2 (aq) + 2e– –> 2Br– (aq)
Cl2 (aq) + 2e– –> 2Cl– (aq)
S2O82-(aq) + 2e– –> 2SO42- (aq)
Zn(s) –> Zn2+(aq) + 2e–
H2 (g) –> 2H+(aq) + 2e–
Sn2+(aq) –> Sn4+(aq) + 2e–
Fe2+ (aq) –> Fe3+(aq) + e–
2. The Concept of Oxidation and Reduction
To make it simpler and easier to study about difference between oxidation and reduction, here a basic concept of oxidation and reduction.
The oxidation and reduction using the help of oxygen was first identified by Lavoiseur. The concept is in oxidation one substances should accept oxygen while in reduction, the other substances need to give their oxygen. For example,
FeO + CO –> Fe + CO2
Its a reaction from ferrous oxide ( FeO) and carbon monoxide ( CO). In the reaction above ferrous oxide loses its oxygen, be reduced, thus called as oxidant or oxidation agent. The oxygen coming from ferrous oxide transfer to carbon monoxide, means oxidized. Thus oxygen act as reductant or reduction agent.
As well as oxygen, hydrogen can also be involved in oxidation and reduction reaction. Oxidation means to give hydrogen while reduction means to accept hydrogen. For example,
H2 + H2CCH2 –> H3C-CH3
Its a reaction between ethylene gas ( H2CCH2) and ethane gas ( H3CCH3). The hydrogen molecule loses its electrons, make them act as oxidant, because its be reduced. The hydrogen atom transfer to ethylene, thus make ethylene be oxidized and act as reductant.
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Its easier to make an oxidation and reduction reaction when there is an oxygen involve, but the problem is that sometimes there are the substances that is not including oxygen such as magnesium and chlorine. It will be hard to determine the accept and give concept between those two. Thus to make it easy try to achieved it by transferring their electron(s). In oxidation, magnesium supposed to give electron(s) and chlorine to accept that electron(s). This equation called as half-reaction, both of the reaction should be shown separately to make it easier. For example,
Mg + Cl2 –> MgCl2
Its hard to determine using transferred oxygen method, thus better used electron transferred method.
Mg –> Mg2+ + 2e–
Cl2 + 2e– –> 2Cl–
The magnesium on the example above shown to gain its electrons, means be oxidized, thus means magnesium is the one who accept the electrons and called as reductant . Meanwhile chlorine is the one who accept the electrons, make chlorine as reductant in the equation above.
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3. Determine of Oxidation number
In order to determine whether some reaction can be called as oxidation and reduction reaction, we must assign some number of oxidation to the element first, after that to know which one is oxidized and which is reduced we should know the concept to assign oxidation number. Because it is a hard concept, thus the rule or standardization for assigning oxidation number was created. Here the following step to guide assigning oxidation number to each element.
- The total number of substances n the reaction will always equal 0.
- Oxidation number for oxygen will always -2, except for peroxide, the oxidation number is -1, i.e H2O2.
- Oxidation number for hydrogen will always +1, except for hydrides, the oxidation number is -1, i.e NaH.
- Oxidation number for alkali metal is +1 and for alkaline earth metal is +2.
- For poly atomic, the number of oxidation is determined, thus the total will always be the same number as the charge of ion(s).
For example, iron can be Fe, Fe2+, or Fe3+ depends on the reaction condition they are involved.
Fe2+ –> Fe + 2e–
Fe3+ –> Fe + 3e–
The oxidation number for each Fe, Fe2+, or Fe3+ are 0, +2, and +3. Another example:
2PbS(s) + 3O2(g) –> 2PbO(s) + 2SO2(g)
+2 -2 0 +2 -2 +4 -2
We can see as the changing of the oxidation number on the left and right side. The oxidation number of S increase from -2 to +4, thus S is oxidized and PbS as reductant. The oxidation number of O decrease from 0 to -2, thus oxygen is an oxidant.
4. The Equation of Oxidation and Reduction
In order to make oxidation and reduction reaction balance thus the equation should be done to achieve it.
- Oxidation Number
- Determine the elements involve in equation. Choose the oxidant and reductant. Then identify the change number in every elements.
- Sum up the number in equation thus have the same total number in both side.
- To keep the equation balance, the ions that involve in equation should be added in both side.
[tab title=”Example of Oxidation Reactions
+3 -2 +2 -2 0 +4 -2 Reduction: 3 e- + Fe+3 → Fe
Fe2O3 (s) + CO(g) → Fe(s) + CO2(g) Oxidation: C+2 → C+4 + 2 e-
The lowest common multiple of 2 and 3 is 6, so there must be 6 electrons gained and 6 electrons lost
2(3 e- + Fe+3 → Fe)
6 e- + 2 Fe+3 →2 Fe
6 e- + Fe2O3 →2 Fe
(There should be 2 Fe atoms on each side of the equation – Fe2O3 already has 2 Fe, but Fe has only 1, so it needs a coefficient of 2)
3(C+2 → C+4 + 2 e-)
3 C+2 →3 C+4 + 6 e-
3CO → 3 CO2 + 6 e-
(There should be 3 C atoms on each side of the equation, so both CO and CO2 need a coefficient of 3)
Add the 2 half-reactions and verify that the result is balanced:
Fe2O3 + 3 CO → 2 Fe + 3 CO2
- Half Reaction
- Determine the elements involve in equation, balance the equation except for oxygen and hydrogen.
- Add an appropriate number of H2O’s to balance the number of oxygen on both side of the equation.
- Add an appropriate number of H+’s to balance the number of hydrogen on both side of the equation.
- Add an appropriate number of e– to equalize the number of electricity on both side.
- Balance the number of electron lost in the half-oxidation equation same as the number gained in the half-reduction equation.
- Add the two equation together.
[tab title=”Example of Oxidation Half Reaction
I– (aq) + H+ (aq) + Cr2O7-2(aq) → I2 (s) + Cr+3(aq) + H2O (l)
(Oxidation half-reaction) (Reduction half-reaction)
Half-reactions I(aq) – → I2 (s) Cr2O7-2 (aq) → Cr+3( aq)
Balance elements 2 I(aq) – → I2 (s) Cr2O7-2 (aq) → 2 Cr+3 ( aq) (except H and O)
Add H2O 2 I( aq) – → I2 (s) Cr2O7-2(aq) → 2 Cr+3(aq) + 7 H2O ( l)
to balance O’s
Add H+ 2 I( aq–) → I2 (s) 14 H+ (aq) + Cr2O7-2 (aq) →
to balance H’s 2 Cr+3 (aq) + 7 H2O ( l)
Add electrons 2 I ( aq) – → I2 (s)+ 2 e– 6e– + 14 H+aq) + Cr2O7-2 (aq) → to balance charges 2 Cr+3 (aq) + 7 H2O ( l)
Use coefficients 3(2 I( aq) – → I2 (s)+ 2 e– ) 6e– + 14 H+ (aq) + Cr2O7-2 (aq) →
to match # of e- 2 Cr+3 (aq) + 7 H2O ( l)
Add half-reactions 6 I ( aq) – →3 I2 (s)+ 6 e– 6e– + 14 H+( aq) + Cr2O7-2 (aq) →
2 Cr+3 (aq) + 7 H2O ( l)
6 I– (aq) + 14 H+( aq) + Cr2O7-2 ( aq) → 2 Cr+3 ( aq) + → 3 I2 (s) + 7 H2O ( l)
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Examples for oxidation and reduction reaction in daily life
Here are the example of reduction and oxidation uses in daily life:
Combustion means burning some materials to make it or to change it into another materials. Combustion is the very basic and the most happen oxidation and reduction reaction in our daily life. This is a reaction of carbon when its burn.
C + O2 –> CO2
And it is the reaction when gasoline burn.
2 C8H18 + 25 O2 –> 16 CO2 + 18 H2O
Rust can also be called corrosion, which happen when metals react with oxygen to form compound that is oxides. Rust almost have similar concept as combustion except that rust is more slowly compare to combustion.
4 Fe + 3 O2 –> 2 Fe2O3
Decay is the reaction happen when living creatures die. when plant, animal, even human die the compound that composed it start to react to oxygen. The reaction pretty much similar to those gasoline reaction but it way more slower than gasoline reaction. This is the reaction that happen in a dead plant.
Cx Hy Oz + O2 –> CO2 + H2O
In order to make their own energy supplier, green plants need photosynthesis to obtain it. They convert carbon monoxide and water with the help of sunlight to produce their own nutrition, such as carbohydrates.
6 CO2 + 6 H2o –> C6H12O6 + 6 O2
The oxidation and reduction theory can be simply said as the reaction of losing and gain electron from one element to other element in order to create or bond the element into one solid compounds. The oxidation and reduction reaction basically is one of the most fundamental chemistry reaction that happen in our daily life, we may not able to recognize them just by seeing the thing but if we know about the oxidation and reduction theory we may know how the phenomenon was made or what compositions it was made. Hope this content can help you to understand about the what is difference between oxidation and reduction.
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