dantiberian Posted February 20, 2007 Posted February 20, 2007 Ok for chem we have to work out the ratio for black powder from the equation 2-KNO3 + 3-C + S = 3-CO2 + N2 + K2S After calculating Mass Ratio e.t.c. i came up with the percentages 74.8 KNO3 13.3 C and 11.8 Sulfur. This is obviously different to the common 75:15:10 ratio most commonly quoted. What could be the reason for the differences?
Mumbles Posted February 20, 2007 Posted February 20, 2007 A few reasons 1) That is an extremely over simplified formula. There are over 30 products from BP combustion. 2) Stoiciometric isn't always the best for practical applications. 3) It's not that different. 4) Ratios are often rounded off to even numbers of weighing and calculating ease.
dantiberian Posted February 20, 2007 Author Posted February 20, 2007 I realise it is not a big difference but i was just curious. Do you have a link to explain the 30 products from BP? What is better than Stoiciometric then?
DeAdFX Posted February 20, 2007 Posted February 20, 2007 Well stoichiometric is a theoretical calculation. Practical/real life figures are somewhat better but it is always a good idea to do the calculations before you conduct an experiment. For pyrotechnics using stoichiometry isn't the most useful tool. Its good for showing what will generally happen.. such as Ba(ClO3) + organic crap ---> BaCl2 + CO2 + H2O + energy + green light. Whats is better than Stoiciometric then? Well if you are interested in making new pyrotechnic formulas then the only thing I can suggest is trial and error and a little common sense. One would obviously expect a mixture of 85% shellac and 15%Ba(ClO3)2 to be a fairly worthless green pyrotechnic mixture. If you are making blue star compisitions hess's law might be handy but other than that trail and error seems to be the one of the better routes for amateur stuff.
Mumbles Posted February 20, 2007 Posted February 20, 2007 It's not the 30+ products I was talking about, but it is probably a dozen. Page 42-44 in Chemistry of Powder and Explosives. I'll see about digging up the source for the 30+. http://www.sciencemadness.org/library/book..._explosives.pdf
asilentbob Posted February 23, 2007 Posted February 23, 2007 There are alot of different ratios people go by. Some were made in a specific area that only had a certain purity of chemicals. Not all charcoals are created equal for instance. Some ratios are tweaked to produce a maximum of gases or to burn very fast or slow and dependable like in fuses. So you can take what you found out on your own back to your teacher and they should accept it. You can also tell them that their equation is only one of many many many possible routes. Chemisty classes have to simplify things sometimes. For instance heating potassium chlorate expells oxygen according to the lessons, but one can make a bit of potassium perchlorate and potassium chloride by heating potassium chlorate too... Theres alot of little things they just don't mention... Chemistry just has so damn many little things like that.
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