making nitrocellulose

[Itoero]

hi,

I'm going to make nitrocellulose using 5g cotton, 50g KNO3 and 80ml H2SO4.

Will these quantities work?

 

I'll do it outside.

Do I have use a cooling bath when it's 5°C outside?

[imatfaal]

I would suggest that mucking around with Sulphuric Acid to produce a highly flammable substance is the sort of experiment that should be done AFTER you know the theory, the quantities, the reaction, and the necessary safety precautions - ie NOT as a part of the learning process

[StringJunky]

I would suggest that mucking around with Sulphuric Acid to produce a highly flammable substance is the sort of experiment that should be done AFTER you know the theory, the quantities, the reaction, and the necessary safety precautions - ie NOT as a part of the learning process

Yes, I think this is one of those exercises where empirical learning is too risky. Early chemistry is littered with dead and disfigured people doing just that. Forearmed is forewarned.

 

A wise man learns from his mistakes; a clever man learns from the mistakes of others.

Edited January 20, 2016 by StringJunky

[Itoero]

I made nitrocellulose several times, I just don't know the quantities anymore.

It's the first time I use KNO3.

 

On Youtube I saw a guy making it outside without a cooling bath and it worked.

[imatfaal]

I made nitrocellulose several times, I just don't know the quantities anymore.

It's the first time I use KNO3.

 

On Youtube I saw a guy making it outside without a cooling bath and it worked.

Are you sure this is legal in your jurisdiction? If your country of posting is accurately listed you live in a regime that is undergoing severe and rapid changes to certain areas of enforcement (in this very area) even if not actual statutory change.

[Itoero]

Are you sure this is legal in your jurisdiction? If your country of posting is accurately listed you live in a regime that is undergoing severe and rapid changes to certain areas of enforcement (in this very area) even if not actual statutory change.

huh? Why do you think that?

[imatfaal]

huh? Why do you think that?

 

There were two statements

 

possibly illegal. Cos it is specifically illegal in quite a few EU countries if the manufacture leads to a high enough concentration. And could easily be interpreted as illegal under countless other pieces of legislation

 

and belgium. Cos Belgium and France are going through paroxysms of panic after those horrific attacks in Paris.

[Itoero]

Where do you got that idea from?

Belgium is not going through paroxysms of panic.

Why would we? Nothing happened.

[imatfaal]

Where do you got that idea from?

Belgium is not going through paroxysms of panic.

Why would we? Nothing happened.

 

Paramilitary police on the streets, highest non warfare security status, requests from the government for the public not to criticise the police, posting pictures of cats when deprived of civil liberties ... panic

 

Anyway this is not politics. You clearly do not understand the chemistry, I am pretty sure that you don't understand the law; a few years ago an amateur chemist who ends up with sapeur pompier having to put out their kitchen would get a slap on the wrist - now they might well get the book thrown at them.

[Itoero]

Paramilitary police on the streets, highest non warfare security status, requests from the government for the public not to criticise the police, posting pictures of cats when deprived of civil liberties ... panic

You believe everything the media says I suppose?

And you do understand that the security status was only in the weeks after the attacks?

Everything is back to normal, except for the Syrian refugees of course.

 

I tried to make nitrocellulose.

When I added the first cotton, the cotton seemed to dissolve. Why is that?

After cooling down I noticed some hard white pieces.

The nitrocellulose also doesn't burn that fast.

[Sensei]

If you have 5 g of cotton, how many moles is it?

If you have 50g KNO3, how many moles is it?

If you have 80ml H2SO4, how many moles is it?

 

If you have 1000 g of water, how many moles is it?

Edited February 7, 2016 by Sensei

[John Cuthber]

If you have 5 g of cotton, how many moles is it?

 

Since you have asked that question, I presume you can answer it.

How many moles do you think it is?

I have to admit I don't know.

If you also don't know, why did you ask?

[Sensei]

Since you have asked that question, I presume you can answer it.

How many moles do you think it is?

I have to admit I don't know.

If you also don't know, why did you ask?

Can I answer by PM.. ?

To not influence answer by OP.

[John Cuthber]

If you like, but perhaps you should explain to the OP why the question isn't as simple as it looks.

You might also want to say why the number of moles matters much.

[Itoero]

When I add cotton to H2SO4 it seems to dissolve.

So when this happens when nitrating, does it mean I should add more KNO3 or just mix the nitrating solution better?

[John Cuthber]

Can I answer by PM.. ?

To not influence answer by OP.

So far, you have sent 3 PMs Only one had an answer in, and that was very wrong so it's just as well you didn't post it here.

 

I'd offer to help Itoero but I really think that people who don't understand the basics shouldn't play with explosives.

[Itoero]

So it's better to try and fail?
practice makes perfect

I've made guncotton many times, but its just some time ago and I always used HNO3.

 

50g KNO3 =0,495 mol

5g cotton =0,028 mol

80ml H2SO4 =1,469 mol (it's not 100% so it's less mol)

1000g H2O =55 mol

Edited February 7, 2016 by Itoero

[John Cuthber]

So it's better to try and fail?

 

Not always; it depends if the failure kills you, maims someone, or gets you arrested.

[Itoero]

I answered Sensei.

[Sensei]

+1

 

What is product of KNO3 and H2SO4.. ?

And in what proportions they need to be.. ?

[John Cuthber]

I answered Sensei.

And you made the same mistake that he did (in his PM).

Did he "help" you?

[Itoero]

Maybe the moles of cotton?

Cellulose does not have a fit amount of glucose molecules so you can't really know how many moles cellulose are in 5g.

 

I think H2SO4+KNO3= HNO3+HKSO4 (is K2SO4 formed when you add more KNO3?)

I need the double amount of H2SO4 compared to HNO3.

Does that mean I need about 3 times as much H2SO4 as KNO3?

Then I need 50g of KNO3 and 80ml H2SO4 just like in my experiment.

 

I did not stir the solution before I added the cotton....kinda stupid of me.

KNO3 and HNO3 are both less dense then H2SO4.

So when you add KNO3 slowly, most of the HNO3 will stay on top while the unreacted H2SO4 stays at the bottom.

Can that be the cause the cellulose seemed to dissolve and the one that didn't dissolve is of a very low quality...?

[John Cuthber]

-That's right.

The number of moles of cotton is essentially not possible to know- because we don't know the molecular weight.

In fact, because the cotton has lots of different sized cellulose molecules, there isn't even a single "average" molecular weight.

There are three commonly used ones and the details are here

https://en.wikipedia.org/wiki/Molar_mass_distribution

though they don't matter much to the problem of nitrating cotton.

(the difference is a bit like the joke about the butcher who makes cheap meat pies. He says the pies are a 50 ;50 mix of lamb and horse. He mixes 1 horse and one lamb.)

 

 

Anyway, as I say that doesn't really matter here.

The first thing you need to do is say what you mean by making "nitrocellulose".

You say you test it by seeing how fast it burns so I'm guessing that you want the version with a lot of nitrate groups, but if you want it to use as a plastic, you would probably want a less nitrated version.

Without deciding on that, you can't really do a lot with the "number of moles" thing that Sensei was so keen on.

 

Let's assume - just to be different, that you are making nominally "dinitrocellulose". That means that for each glucose unit in the cellulose you want to add two nitrate groups.

It has a molecular formula that roughly corresponds to C₆H₈(NO₂)₂O₅

 

And let's at least work through the calculation- though in this case it's not as helpful as you might expect.

So, for each 6 carbon atoms there are 2 nitrogen atoms. And so the nitrogen weighs (2*14)/(6*12) times as much as the carbon.

There's 38.9% as much nitrogen there as carbon.

 

Now we need to know how much carbon there is in 5g of cotton.

Well, according to wiki

https://en.wikipedia.org/wiki/Cotton

"The fiber is almost pure cellulose."

and I'm prepared to believe it for this sort of thing.

So how much carbon is there in 5 g of cellulose?

Well, again, we have a molecular formula (C₆O₅H₁₀)_n

And from that we can see that the proportions of the weights are

12*6 : 5*16 : 10*1 or

72 : 80 : 10

and so the proportion of carbon is 72/ (72+80+10) = 44.4%

so 5 grams of it has 2.22 grams of carbon.

And that would need 2.22/ 0.389 = 5.7 grams of nitrogen

 

It's getting late, so I will let you work out how much potassium nitrate you need to get that much nitrogen.

 

But now I'm going to break the bad news to you.

The reaction doesn't go nicely according to the equation you might write out for it.

At least some of the nitrogen is lost by oxidising the cellulose (and some of the impurities in it) which converts it to a mixture of oxides of nitrogen.

So, you can calculate the number of moles (as long as you know what the molar mass is).

And you can calculate the mass of sulphuric acid needed to convert that many moles of nitrate to nitric acid.

 

And it won't help much.

 

Partly because the sulphuric acid is also the solvent, and partly because it's purpose isn't just to make nitric acid.

There are at least two possible pathways for the reaction and which one happens probably depends on temperature, concentration etc.

Either the sulphuric acid reacts with the nitric acid to produce nitronium ions that attack the cellulose

2 H2SO4 + HNO3 => 2 HSO4(−) + NO2(+) + H3O(+)

 

or the acid protonates they hydroxyl groups on the cellulose, and those react with the nitric acid.

Indeed, it's possible that both reactions happen.

 

But, in any case you need an excess of the sulphuric acid.

 

How much of an excess do you need?

I don't know; I never tried.

I gather that, for making gun-cotton a mixture of about 2 parts of sulphuric to one of nitric is about right.

And with that sort of "precision" you can understand why I didn't bother using accurate atomic weights for N,C, H and O or worry very much about the purity of the cellulose.

[Sensei]

And let's at least work through the calculation- though in this case it's not as helpful as you might expect.

So, for each 6 carbon atoms there are 2 nitrogen atoms. And so the nitrogen weighs (2*14)/(6*12) times as much as the carbon.

There's 38.9% as much nitrogen there as carbon.

 

Now we need to know how much carbon there is in 5g of cotton.

Well, according to wiki

https://en.wikipedia.org/wiki/Cotton

"The fiber is almost pure cellulose."

and I'm prepared to believe it for this sort of thing.

So how much carbon is there in 5 g of cellulose?

Well, again, we have a molecular formula (C₆O₅H₁₀)_n

And from that we can see that the proportions of the weights are

12*6 : 5*16 : 10*1 or

72 : 80 : 10

and so the proportion of carbon is 72/ (72+80+10) = 44.4%

so 5 grams of it has 2.22 grams of carbon.

And that would need 2.22/ 0.389 = 5.7 grams of nitrogen

And it's wrong result.

 

2.22 g of carbon / 12 g/mol = 0.185 mol (all C) / 6 (atoms of C) = 0.030833 mol * 2 * 14 g/mol (of N) = 0.8633 g of N

which is the same as

2.22 g * 0.389 = 0.8633 g

 

Going my initial thought (and independent Itoero from post #17)

5 g * 0.91 (91% of cellulose in Cotton) = 4.55 g / 162.144 g/mol = 0.028 mol * 2 * 14 g/mol (of N) = 0.784 g of Nitrogen needed.

(difference is caused by initial multiplication by 0.91)

 

Although I don't understand why you calculate amount of Nitrogen, while we're interested in nitric acid in the first place.

0.028 mol * 2 * 63.012 g/mol = 3.53 g of HNO3 needed.

 

ps. 72+80+10 = 162

You said, it's not even closer to that value.

I was not talking about mass of whole long chain compound, but single monomer unit. Itoero interpreted it correctly.

Edited February 9, 2016 by Sensei

[John Cuthber]

I cited both a source and a reason for assuming that cotton is 100% cellulose

You, on the other hand, have pulled a spuriously accurate figure of 91% out of thin air.

 

YOu say you don't understand how the amount of nitrogen is important, well, you are trying to work out how much of the nitrogen source- KNO3 you need.

Don't you see how one tells you the other?

If I need 1 gram of nitrogen and the KNO3 contains x % of it then I need 100/x grams of it.

 

"ps. 72+80+10 = 162
You said, it's not even closer to that value."

 

I never said what that value was (though I divided 78 by it)

 

I did say (in a PM for those who are struggling to follow this) that the molecular mass of cellulose is nowhere near 162, and that statement is perfectly correct isn't it?

It's about 162 n where n is the degree of polymerisation.

Typically that's about 1000 to 10,000.

according to this

https://en.wikipedia.org/wiki/Cellulose

 

​So your estimate of the number of moles is wrong by a factor of about 1000 or 10,000.

 

"I was not talking about mass of whole long chain compound, but single monomer unit."

That's not what you said. You said moles of cellulose.

 

You never actually said what you were talking about and that's part of the problem. But the number of moles of a substance is perfectly well defined and you got it very badly wrong.

 

Once again, you are failing to accept that you made a clumsy mistake.

 

https://en.wikipedia.org/wiki/Law_of_holes

Edited February 9, 2016 by John Cuthber