studybloomer
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Hi, I'm confused as to how many water molecules are produced in a condensation reaction. Let me explain what I mean below:

Im looking at the making of Kevlar:

So, I have 1 molecule of 1,4 diamino benzene and 1 molecule of benzene -1,4-dicarboxylic acid, which will give me 1 molecule of kevlar and 1 molecule of H20. This is due to the condensation reaction.

Now to the bit I'm confused on :
So if i have 'n' number of 1,4 diamino benzene and'n' number of benzene -1,4-dicarboxylic acid , this will give me 'n' number of kevlar , which makes sense. How many water molecules are produced?
On chemrevise: it states 2n-1 H20 is produced.However on CGP, it states 2n H20 is produced. This gives two different answers. Does any one know?
Thanks ,
Help would be much appreciated!!
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charco
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(Original post by studybloomer)
Hi, I'm confused as to how many water molecules are produced in a condensation reaction. Let me explain what I mean below:

Im looking at the making of Kevlar:

So, I have 1 molecule of 1,4 diamino benzene and 1 molecule of benzene -1,4-dicarboxylic acid, which will give me 1 molecule of kevlar and 1 molecule of H20. This is due to the condensation reaction.

Now to the bit I'm confused on :
So if i have 'n' number of 1,4 diamino benzene and'n' number of benzene -1,4-dicarboxylic acid , this will give me 'n' number of kevlar , which makes sense. How many water molecules are produced?
On chemrevise: it states 2n-1 H20 is produced.However on CGP, it states 2n H20 is produced. This gives two different answers. Does any one know?
Thanks ,
Help would be much appreciated!!
If you draw it out (simplified) you will see that it's 2n-1.

Represent one monomer by A and the other by B

A-(water)-B-(water)-A-(water)-B
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studybloomer
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oh that makes sense-thanks very much!!!!
Do you know how to draw out:
-CO(CH2)4CONHC(CH3)2CH2O- this polymer as both amide and ester linkage?
Sorry for the many questions

did not mean for the spolier thingies- i dont know how to get rid of them
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(Original post by charco)
If you draw it out (simplified) you will see that it's 2n-1.

Represent one monomer by A and the other by B

A-(water)-B-(water)-A-(water)-B
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username3249896
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The different answers are because of the water molecule formed when the bridging bonds to the rest of the polymer are formed.

HO2C-C6H4-CO2H + H2N-C6H4-NH2 -> -C(O)-C6H4-CONH-C6H4-NH- + 2H2O
n HO2C-C6H4-CO2H + n H2N-C6H4-NH2 -> -(C(O)-C6H4-CONH-C6H4-NH-)n + 2n H2O

I would say 2n.
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charco
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(Original post by BobbJo)
The different answers are because of the water molecule formed when the bridging bonds to the rest of the polymer are formed.

HO2C-C6H4-CO2H + H2N-C6H4-NH2 -> -C(O)-C6H4-CONH-C6H4-NH- + 2H2O
n HO2C-C6H4-CO2H + n H2N-C6H4-NH2 -> -(C(O)-C6H4-CONH-C6H4-NH-)n + 2n H2O

I would say 2n.
The crosslinks are hydrogen bonds, not covalent bonds.
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ChemistryWebsite
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(Original post by charco)
If you draw it out (simplified) you will see that it's 2n-1.

Represent one monomer by A and the other by B

A-(water)-B-(water)-A-(water)-B
(Original post by BobbJo)
The different answers are because of the water molecule formed when the bridging bonds to the rest of the polymer are formed.

HO2C-C6H4-CO2H + H2N-C6H4-NH2 -> -C(O)-C6H4-CONH-C6H4-NH- + 2H2O
n HO2C-C6H4-CO2H + n H2N-C6H4-NH2 -> -(C(O)-C6H4-CONH-C6H4-NH-)n + 2n H2O

I would say 2n.
I would say 2n is a very good approximation but 2n-1 is strictly correct.
2n would be correct for a polymer chain of infinite length.
2n-1 would be correct for a 'real' polymer chain which has an end. The end monomer doesn't form a water molecule by making an amide link to the next monomer simply because there isn't a next monomer unit.
Last edited by ChemistryWebsite; 1 year ago
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username3249896
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(Original post by charco)
The crosslinks are hydrogen bonds, not covalent bonds.
No I didn't mean the crosslinks. The 'dangling bonds'
-C(O)-C6H4-CONH-C6H4-NH-
I am aware about the structure of kevlar.
I am not sure why you think (or think that I think) water is formed when hydrogen bonds are formed.
(Original post by ChemistryWebsite)
I would say 2n is a very good approximation but 2n-1 is strictly correct.
2n would be correct for a polymer chain of infinite length.
2n-1 would be correct for a 'real' polymer chain which has an end. The end monomer doesn't form a water molecule to the next monomer simply because there isn't a next monomer unit.
I thought so too. Thanks

I only meant to point out that the reason for the difference between CGP and chemrevise was the water molecule formed to extend the chain.
I am sorry to have given my wrong opinion.
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