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KNO3 Reaction


jowrose
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Ok I was trying to come up with a balanced equation for the reaction between KNO3 and sucrose, C12H22O11. I think I figured out the relative amounts of reactants by using the generally accepted ratio (by weight) of 3 KNO3 to 2 Sucrose.

 

4 C12H22O11 + 9 KNO3 --> ?

 

Or, if this is better;

 

8 C12H22O11 + 18 KNO3 --> ?

 

I did some thinking as to possible products, and here's my best guess:

 

8 C12H22O11 + 18 KNO3 --> 87 C + 88 H2O + 18 KNO2 + 9CO2

 

My idea was that the H and O atoms from sucrose form water, leaving elemental carbon, some of which combines with oxygen from the decomposition of the KNO3, leaving KNO2. I considered NO2 as a product, but dismissed it because I didn't think K2O would form. I really don't know much about chemistry, so this is really just a somewhat educated guess. Any help is appreciated; I'm not asking anyone to come up with the whole reaction, just maybe a few hints as to what the products are.

 

Thanks,

 

john

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The following reaction is a fairly good description. It is somewhat idealized, because you'll always have side reactions, where KNO2 and NOx are formed, but the main reaction is as follows:

 

5 C12H22O11 + 48 KNO3 ---> 24 K2CO3 + 55 H2O + 24 N2 + 36 CO2

 

If you mix very finely powdered KNO3 and sugar in the molar ratio's as described above, then you'll see that the reaction product is mainly a white solid, which, when immersed in an acid, gives a lot of bubbles.

 

Side reactions produce carbon, some tarry/caramel-like material and some KNO2.

 

I derived the reaction equation, based on the observation that the main solid product is potassium carbonate and the gaseous products, usually are H2O and CO2 from combustion and nitrate is reduced to N2. Given these reaction products, it is easy (though somewhat cumbersome by hand) to balance the equation.

For the last thing I've written a nice program, which does the dirty work for me.

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All instructions for creating rocket fuel from KNO3 and sucrose call for the ingredients to be mixed in a ratio of 3:2 (KNO3:sucrose). Doing molar mass calcs, I found the molar ratio to be 9 mol KNO3 to 4 mol sucrose. Does that create different products from the equation you came up with, or just much messier products? If I was to mix the ingredients in the ratio given by your equation, would I get a better reaction (for rocket fuel, at least)?

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It'll give much messier products. With that ratio the mix is strongly deficient in oxidizer, so the sugar will not burn completely.

 

However, keep in mind that the optimal chemical mixture does not always need to be the optimal mix for rocketry purposes. It might be that the optimal chemical mix as according to my equation burns too fast for rocketry purposes. The amount of gas produced may be too much, etc. I'm not an expert on this, making a good rocket partly is chemistry, but constructional issues and speed of combustion also are very important factors for success.

 

YT, could you please jump in :)?? You probably better can help with the rocketry part.

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there isn`t really much I can add, you`re quite correct that the ideal is to have as little in way of solid products (nozzel blockers) as possible and the max amount of gas as you can get at a fast rate. the only real design problem with such rockets are when excess oxidiser is used and starts attacking the cardboard tube that contains the grain and ulimately rupturing it, I use a thin skim of plaster on the inside of the tube to prevent this and it also gives a better bonding surface for the grain.

my actual Recipe is still packed away in a box somewhere, I didn`t use any maths to work it out, it was purely trial and error and dozens of notes taken about 20 years ago, I went for the burn that left the least residue.

don`t forget also, that you`ll have to factor in the Dextrin also, even though it`s only a Percent (1-2%) of the fuel, to be Truly efficient, it`s worth factoring it in.

do NOT try the candy Rocket synth (melting the mixture) it`s courting disaster!

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do NOT try the candy Rocket synth (melting the mixture) it`s courting disaster!

 

Heh, happened to me once, even though I only do 5grams at a time. I wasn't paying attention and it overheated and went off. I assume if you have a electric stove its much safer as temperatue control is easier.

I don't really like the Dextrin idea, takes to long to dry (taking note in the hygroscopic of both sucrose and kno3) even if you add 1:1 water to alcohol

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yes, it can take a while, but in a warm dry place (a shelf above a radiator) you can have 100`s done in a week, and perfectly safely.

but rocketry isn`t a thing to be rushed or cut corners with anyway, and when offset against the risks involved, a little patience pays dividends ultimately :)

natuarly the Hollow core rockets dry the fastest, but a good weeks drying time isn`t much to ask, and they Do store well without grain shrinkage (also a bonus).

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I've always melted the mixture before, and have only had one accident (given it was with about 300 grams, and indoor no less...). What i'm thinking about now is trying to create a rocket with copper piping. I found this special piece at the home depot, and i'm going to fill it with the fuel and then secure a cap to the end. I'll drill a hole at the end, insert a wick, and see if it flies... I did a little testing by placing a rocket on this car made of Knex (yeah, it's not very scientific) and shooting it down my street, but the cap blew off with all the pressure so I'm going to find a better way to secure it.

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I`m not sure I want to hear anymore to be honest, in effect you`re doing almost everything propper rocket sites tell you Not to do, and making something akin to a pipe bomb that you hope doesn`t explode. :(

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That last sentence, in retrospect, is extremely ironic. Here's a not-so-nice story...

 

Once upon a time (about 2 hours ago), me and my friend went to the middle of the street with our knex/rocket car. I was videotaping (though I didn't get any very good footage), and my friend was watching. I lit the fuse, and we both backed up about 20 feet. The car moved forward a bit, and then with a massive BOOOOM it blew up. We only found about 10 percent of the knex car, along with a completely inside-out piece of copper piping. Industrial copper piping.

 

Now, in true scientific fashion, I will analyze the results of my highly unscientific experiment. My rocket was composed of a piece of copper pipe (one end was sealed in the factory into a bullet-esque shape) and an end cap that had three very small holes drilled into it. The holes were I think 1/16 inch diameter (just a wee bit too small, methinks...). The cap was secured to the pipe fitting with nails. I drilled 2 holes into both the cap and pipe, and pounded a nail into each corresponding hole, securing the cap. When the pressure built up to, oh, a few hundred psi, the copper ruptured and let out all the gases with tremendous force. The knex car did not survive.

 

Now, I know I'm a "kewl" or whatever you people like to call idiots like me who do stupid things. And I can say with certainty that I will never try what I did today ever again. It scared the hell out of me. I'll stick to smoke bombs and REAL scientific experiments.

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Now, I know I'm a "kewl" or whatever you people like to call idiots like me who do stupid things. And I can say with certainty that I will never try what I did today ever again. It scared the hell out of me. I'll stick to smoke bombs and REAL scientific experiments.

Hopefully you've learnt from this. Next time, please do not describe in full detail how you did these stupid things. You might bring other people to some strange ideas...

Indeed, try to do real scientific experiments. Chemistry is so much more than smoke, fire and noises :) .

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