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Topic: Moles of carbon of a polymer  (Read 3413 times)

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Offline hguzman

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Moles of carbon of a polymer
« on: November 14, 2016, 02:25:40 PM »
Hello all,

This is my problem. I want to calculate how many moles of carbon are contained in a polymer as to make it react with another compound (AB) in a determined proportion. Let's say C/AB = 0.2.  I only have the average molecular weight of the polymer, 200000 Da and the formula of the monomer. How do I make such calculation ?.

Offline Borek

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Re: Moles of carbon of a polymer
« Reply #1 on: November 14, 2016, 03:44:32 PM »
What about using the carbon percentage to find its mass in the given sample?
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Offline hguzman

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Re: Moles of carbon of a polymer
« Reply #2 on: November 14, 2016, 06:48:31 PM »
Hey Borek,

I need the moles so I can maintain the molar ratio of C/AB = 0.2, and subsequently, calculate how many grams of the polymer should be added to the reaction.

Thanks.

Offline Arkcon

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Re: Moles of carbon of a polymer
« Reply #3 on: November 14, 2016, 07:29:57 PM »
OK.  Since you're dealing with polymers produced on this planet by typically understood chemistry, you have an average, which covers the range of possible polymer lengths.  What you seem to want, an exact number, can't be found.

Now you can take a sample, try to figure out how much is there analytically, and use that number, like Borek: suggested.

Or you can just add one reactant in vast excess, and wash it away by some means, as is often done in production chemistry.
Hey, I'm not judging.  I just like to shoot straight.  I'm a man of science.

Offline hguzman

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Re: Moles of carbon of a polymer
« Reply #4 on: November 14, 2016, 11:27:17 PM »
Arkcon,

You seem a little annoyed by my question. Let me be more clear about it, can I calculate the moles of carbon present in the polymer using the formula of the MONOMER (which is known) and the average molecular weight (which is known) ?.

Perhaps I did not read that in Borek's answer, but he did not suggest any analytical technique to calculate the carbon percentage.

On the other hand, regarding your suggestion, I want the exact number, precisely, to avoid using more than it is required since the excess will produce an undesired compound that cannot be "washed away" in the likes of all production chemistry facilities in this vast planet that typically dump excess materials in rivers as to maintain production costs at bay.

Thanks.

Offline Borek

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Re: Moles of carbon of a polymer
« Reply #5 on: November 15, 2016, 02:37:01 AM »
Perhaps I have misread your initial post and my first idea was wrong, but - sorry to say that - all the time I have a feeling we are dealing with a trivial, high school level calculations.

You will be reacting an easy to check mass of a polymer, say 10 g. If you have 10 g of a 200000 Da molecules, how many moles is that?
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Offline hguzman

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Re: Moles of carbon of a polymer
« Reply #6 on: November 15, 2016, 09:45:27 AM »
With all due respect, I am not looking for the moles of polymer what I need are the moles of carbon in the polymer. I don't need to assume 10 g of polymer I have the C/AB ratio of 0.2 to make the calculation. Once I fix the moles of AB I will have the moles of carbon that are required for the reaction, now the problem is. Do I make the calculation of the mass of polymer needed using the formula of the monomer of do I have to calculate the amount of carbon contained in the formula of the WHOLE polymer so I can calculate the mass that I need to add ?.

Thank you.

Offline DrCMS

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Re: Moles of carbon of a polymer
« Reply #7 on: November 15, 2016, 11:14:15 AM »
Try doing some work of your own and also try when asking other people for help to be a little less of a f#*king c#%t.

Let me be more clear about it, can I calculate the moles of carbon present in the polymer using the formula of the MONOMER (which is known) and the average molecular weight (which is known) ?.

As a first approximation ignoring the end groups yes.  Is that good enough for you needs? I have no idea whatsoever as you have not explained them clearly.

I want the exact number, precisely, to avoid using more than it is required since the excess will produce an undesired compound that cannot be "washed away" in the likes of all production chemistry facilities in this vast planet that typically dump excess materials in rivers as to maintain production costs at bay.

I suggest that is not true anymore and has been spouted by an idiot who has never worked in a chemical plant. 

Offline hguzman

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Re: Moles of carbon of a polymer
« Reply #8 on: November 15, 2016, 11:23:57 AM »
Why the insults DrCMS ?

Offline Borek

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Re: Moles of carbon of a polymer
« Reply #9 on: November 15, 2016, 11:25:34 AM »
With all due respect, I am not looking for the moles of polymer what I need are the moles of carbon in the polymer.

Then I was right from the very beginning - mass percentage of carbon in the polymer is identical to the mass percentage of carbon in monomer (or a bit different if it is a polycondensate, but still trivial to find), and that's the base for calculations.

Quote
I don't need to assume 10 g of polymer I have the C/AB ratio of 0.2 to make the calculation. Once I fix the moles of AB I will have the moles of carbon that are required for the reaction

If you start with polymer mass you can find the mass and moles of carbon, then the ratio gives you an instant answer in terms of the AB amount. Yes, it can be also done the other way, again using mass percentage of carbon in the polymer to convert between moles and mass.

Sorry, perhaps I am missing something but this question really looks trivial.
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Offline hguzman

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Re: Moles of carbon of a polymer
« Reply #10 on: November 15, 2016, 11:58:39 AM »
Ok, I see your point now Borek.

My apologies for the miscommunication. My bad.

Thank you.

Offline DrCMS

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Re: Moles of carbon of a polymer
« Reply #11 on: November 15, 2016, 12:19:41 PM »
Why the insults DrCMS ?

Because of what you said and the way you've said it. The forum rules say you need to show that you have attempted yourself to get an answer and then ask for advice.  You chose not to do that and when people did offer help you were dismissive and condescending.

With all due respect

We all know that means with absolutely no respect whatsoever.
 

in the likes of all production chemistry facilities in this vast planet that typically dump excess materials in rivers as to maintain production costs at bay.

Statement like that play on the worst fears of the chemphobic public and do our profession no help at all.  It is also patently not true of the vast majority of chemical plants worldwide.  It is definitely not true of those in the western world and increasing no longer true for those previous polluters in China and India either.

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