Oxidation Reduction Reaction:-
Lets start with its defination, I wont give the lines of the book :) i ll try to clear the basic concept.
1-It Involves the transfer of electrons between two species, by which number of atoms,ions or molecule may fluctuate by gaining or losing electrons. e.g Combustion , photosynthesis, respiration.
2-Oxidation state is actually the number of electrons, that an atom either gains or loses. Some guidelines may help you to understand the oxidation state.
(a)Oxidation state in free stae is zero
(b) sum of oxidation state in atoms of neutral specie is zero and in an ion is equal to ion charge.
Oxidation Reducation Reaction consists of two parts :- i.e
1-Reduced Half:-
In this electrons are gained and oxidation number decreases.
2-Oxidised half:-
in this electrons are lost and oxidation number increases.
LET ME GIVE YOU A TIP :D
1- REMEMBER "OIL AND RIG" Oxidation is Lost And Reduction is Gained .. :D
Then come the oxidation states!
Its VERY SIMPLE. See:
Fe(s) + Sn(aq) -à Fe2O3 (aq) + Sn(s)
Remember: Unreacted state is called zero state or ground state.
You have to remember the tests for reducing agents and oxidizing agents!
for Oxidizing agents:
Aqueous potassium iodide is used. Symbol is KI. And a brown solution is formed if oxidizing agent is present.
Why it turns brown? Because I- oxidizes to I2
for Reducing agents:
Acidified Potassium Dichromate (VI) is used. Symbol is K2Cr2O7. Color changes from orange to green in presence of reducing agent.
Keep visiting the blog :)
Lets start with its defination, I wont give the lines of the book :) i ll try to clear the basic concept.
1-It Involves the transfer of electrons between two species, by which number of atoms,ions or molecule may fluctuate by gaining or losing electrons. e.g Combustion , photosynthesis, respiration.
2-Oxidation state is actually the number of electrons, that an atom either gains or loses. Some guidelines may help you to understand the oxidation state.
(a)Oxidation state in free stae is zero
(b) sum of oxidation state in atoms of neutral specie is zero and in an ion is equal to ion charge.
Oxidation Reducation Reaction consists of two parts :- i.e
1-Reduced Half:-
In this electrons are gained and oxidation number decreases.
2-Oxidised half:-
in this electrons are lost and oxidation number increases.
LET ME GIVE YOU A TIP :D
1- REMEMBER "OIL AND RIG" Oxidation is Lost And Reduction is Gained .. :D
What’s oxidation?
A substance is oxidized if:
1. it gains oxygen or
2. loses hydrogen or
3. loses electrons or
4. increases its oxidation state.
A substance is oxidized if:
1. it gains oxygen or
2. loses hydrogen or
3. loses electrons or
4. increases its oxidation state.
The gain of oxygen is very simple. You have to see which substance
on the product side gained oxygen. Keep in mind that a substance which already
has oxygen can ALSO get oxidized if it gains more oxygen.
for example, 2Ca + O2 --> CaO
Calcium gain oxygen so, we say calcium is oxidized.
Similarly, the loss of Hydrogen is the same. You have to see which substance lost H2
For example, H2S + Cl2-à 2HCl +S
Here, H2S lost Hydrogen so hydrogen sulphide has been oxidized.
Remember: When you’r talking about gain of oxygen, you will pick the element from the product side and say it has been oxidized. However, when you say loss of Hydrogen you will pick the element from the reactant side because thtas the one which lost Hydrogen. You will not say Sulphur has lost H2 but H2S has lost H2
Similarly in reduction it’s the opposite. There is loss of oxygen and gain of hydrogen.
Loss of Oxygen:
Zn +CuO à ZnO + Cu
CuO lost Oxygen, so CuO is reduced to Cu. You will NOT say that Copper has reduced, you will say that Copper(II) oxide has reduced to Copper.
for example, 2Ca + O2 --> CaO
Calcium gain oxygen so, we say calcium is oxidized.
Similarly, the loss of Hydrogen is the same. You have to see which substance lost H2
For example, H2S + Cl2-à 2HCl +S
Here, H2S lost Hydrogen so hydrogen sulphide has been oxidized.
Remember: When you’r talking about gain of oxygen, you will pick the element from the product side and say it has been oxidized. However, when you say loss of Hydrogen you will pick the element from the reactant side because thtas the one which lost Hydrogen. You will not say Sulphur has lost H2 but H2S has lost H2
Similarly in reduction it’s the opposite. There is loss of oxygen and gain of hydrogen.
Loss of Oxygen:
Zn +CuO à ZnO + Cu
CuO lost Oxygen, so CuO is reduced to Cu. You will NOT say that Copper has reduced, you will say that Copper(II) oxide has reduced to Copper.
Gain of Hydrogen:
H2 + Cl2 --> 2HCl
Here, Chlorine has gained Hydrogen so chlorine is oxidized.
H2 + Cl2 --> 2HCl
Here, Chlorine has gained Hydrogen so chlorine is oxidized.
Ok, the story is simple till oxygen and hydrogen, right?
Now when it comes to gaining and losing electrons, and
oxidation states, it boggles students.
Remember this by… OIL
RIG >
Oxidation
Is
Loss of electrons
Reduction
Is
Gain of electrons
Oxidation
Is
Loss of electrons
Reduction
Is
Gain of electrons
Now how to do it. See, For example, there is a reaction:
Mg + Cl2 àMgCl2
Now you wanna know if it has lost electrons or gained electrons.
Now, Mg has +2 ions in its ionic state, right? Means, it lost 2 electrons.
And Cl has -1 but there are 2 Cl so 2(-1) = -2 means it gained 2 electrons. So basically Mg gave its 2 electrons to form MgCl2
Who lost electrons? Magnesium.
So whose oxidized? Magnesium.
So whichever element loses electrons, is oxidized.
Similarly, whichever element gains electrons is reduced.
Now, Mg has +2 ions in its ionic state, right? Means, it lost 2 electrons.
And Cl has -1 but there are 2 Cl so 2(-1) = -2 means it gained 2 electrons. So basically Mg gave its 2 electrons to form MgCl2
Who lost electrons? Magnesium.
So whose oxidized? Magnesium.
So whichever element loses electrons, is oxidized.
Similarly, whichever element gains electrons is reduced.
Then come the oxidation states!
Its VERY SIMPLE. See:
Fe(s) + Sn(aq) -à Fe2O3 (aq) + Sn(s)
Remember: Unreacted state is called zero state or ground state.
Fe0 + Sn2+ à Fe3+ + Sn0
Now what happened. Fe is in ground
state, so its zero. Sn is in aqueous state, means ions, and its valency is therefore 2+. These are the initial ones.
After the reaction, Fe reacted and is in aqueous state. How do you find out its oxidation state?
Fe2O3
we have to find out Fe’s oxidation state so let it be x
2x + 3(-2) = 0 (the oxidation state of oxygen is -2 so we multiply it by 3 since there are three atoms)
Now solve.
2x-6 = 0
x = 6/2
x = 3
So Fe is 3+
(Remember this simple method and you will never do the oxidation states wrong)
Now it was initially 0 and it turned 3+ so there is an increase in oxidation state.
This means, it has oxidized. When there is decrease in oxidation state, it has reduced. Sn was initially 2+ and then it became 0 so it has reduced.
This reaction, which has both oxidation and reduction reactions side by side is known as a redox reaction!
And those elements which help a substance to oxidize are oxidizing agents. And those that help a substance to reduce are reducing agents.
Fe2O3
we have to find out Fe’s oxidation state so let it be x
2x + 3(-2) = 0 (the oxidation state of oxygen is -2 so we multiply it by 3 since there are three atoms)
Now solve.
2x-6 = 0
x = 6/2
x = 3
So Fe is 3+
(Remember this simple method and you will never do the oxidation states wrong)
Now it was initially 0 and it turned 3+ so there is an increase in oxidation state.
This means, it has oxidized. When there is decrease in oxidation state, it has reduced. Sn was initially 2+ and then it became 0 so it has reduced.
This reaction, which has both oxidation and reduction reactions side by side is known as a redox reaction!
And those elements which help a substance to oxidize are oxidizing agents. And those that help a substance to reduce are reducing agents.
You have to remember the tests for reducing agents and oxidizing agents!
for Oxidizing agents:
Aqueous potassium iodide is used. Symbol is KI. And a brown solution is formed if oxidizing agent is present.
Why it turns brown? Because I- oxidizes to I2
for Reducing agents:
Acidified Potassium Dichromate (VI) is used. Symbol is K2Cr2O7. Color changes from orange to green in presence of reducing agent.
Keep visiting the blog :)
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