Is this a redox reaction ? Explain
CaCO3 ----heating----> CaO + CO2
I am a bit confused here because sometimes the same element can get oxidised as well as reduced. Please help me out!
Divyankasc:
I hope someone can help me out!
Answers
Answered by
104
Listen carefully,
To see whether the given reaction is redox reaction or not, we have to look at the change in oxidation number of all elements taking part in reaction i.e. reactant and product both
If the oxidation number of an element increase, then it is oxidation and if it is decreased then it is reduction.
But in the above reaction, the oxidation number of
Ca remains as +2
C remains as +4
and O remains as -2
So, there is no change in oxidation number, so it's not redox reaction.
Actually it is thermal decomposition reaction.
And yes, same element can be oxidized and redused ,both, but it can only be seen through their change in oxidation number
To know the oxidation number,
CaCO₃ - valency of Ca is 2, and this is a metal, so +2
C, valency is 4, it's oxidation number is +4 as it is bonded with O and valency of O is 2 having oxidation number -2 as it is non- metal.
See for example, to find the oxidation number of CO₂
⁻²O=C²⁺²=O⁻²
I hope, now this will help you :)
To see whether the given reaction is redox reaction or not, we have to look at the change in oxidation number of all elements taking part in reaction i.e. reactant and product both
If the oxidation number of an element increase, then it is oxidation and if it is decreased then it is reduction.
But in the above reaction, the oxidation number of
Ca remains as +2
C remains as +4
and O remains as -2
So, there is no change in oxidation number, so it's not redox reaction.
Actually it is thermal decomposition reaction.
And yes, same element can be oxidized and redused ,both, but it can only be seen through their change in oxidation number
To know the oxidation number,
CaCO₃ - valency of Ca is 2, and this is a metal, so +2
C, valency is 4, it's oxidation number is +4 as it is bonded with O and valency of O is 2 having oxidation number -2 as it is non- metal.
See for example, to find the oxidation number of CO₂
⁻²O=C²⁺²=O⁻²
I hope, now this will help you :)
Thanks!
but, how do u know that it isnt changed
do you know to identify oxidation number??
I am really really new to this concept so it will take me time to get it known better and till then i will keep asking some silly questions :P
nah
ummm..okey...i'll edit that..ok
When our teacher was teaching i was absent (absent for a whole month!)
Thanks!
okay, i understand
Answered by
12
The oxidation state can be thought of as the charge that would exist on an atom if it was bonded using 100%ionic bonds where the more electronegative element in each bond gets both electrons leaving the less electronegative atom with one less that it started with.
To know if an element is oxidised check it's oxidation state before and after the reaction and if it changes then you know. If the oxidation state is higher (more positive) the element was oxidised. If the oxidation state is reduced (more negative) the element was reduced.
In your reactants, the Ca is an element and so it is neutral and has an oxidation state of 0. The water has two O-H bonds and in each one the pair of electrons is counted as belonging to the oxygen, making it-2 and leaving both H atoms+1.
In the products, the Ca is in a compound and you can recognise that it has a +2 charge. So the Ca oxidation state changed from 0 to +2. It was oxidised. The hydrogen in the products is in elemental form so it has oxidation state of 0. The H changed from +1 to 0. It was reduced.
In the early days of trying to understand oxidation and reduction or was thought that oxygen was always involved, hence the name. We now know that oxidation can happen without the presence of any oxygen. It involves gain and loss of electrons as I described above.
Try this reaction.
Zn(s)+Cu2+(aq)→Cu(s)+Zn2+(aq)Zn(s)+Cu2+(aq)→Cu(s)+Zn2+(aq)
This time, the zinc is oxidised from 0 to +2 and the copper is reduced from+2 to 0. No oxygen needed.
To know if an element is oxidised check it's oxidation state before and after the reaction and if it changes then you know. If the oxidation state is higher (more positive) the element was oxidised. If the oxidation state is reduced (more negative) the element was reduced.
In your reactants, the Ca is an element and so it is neutral and has an oxidation state of 0. The water has two O-H bonds and in each one the pair of electrons is counted as belonging to the oxygen, making it-2 and leaving both H atoms+1.
In the products, the Ca is in a compound and you can recognise that it has a +2 charge. So the Ca oxidation state changed from 0 to +2. It was oxidised. The hydrogen in the products is in elemental form so it has oxidation state of 0. The H changed from +1 to 0. It was reduced.
In the early days of trying to understand oxidation and reduction or was thought that oxygen was always involved, hence the name. We now know that oxidation can happen without the presence of any oxygen. It involves gain and loss of electrons as I described above.
Try this reaction.
Zn(s)+Cu2+(aq)→Cu(s)+Zn2+(aq)Zn(s)+Cu2+(aq)→Cu(s)+Zn2+(aq)
This time, the zinc is oxidised from 0 to +2 and the copper is reduced from+2 to 0. No oxygen needed.
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