why does potassium nitrate create smoke when mixed with sugar?
Sunday, May 16th, 2010 at
2:48 PM
isn’t the potassium nitrate just an oxidizer and the sugar just bonds it? Thanks, it is very much appreciated!
please explain why, thanks!
I dont get what catalyst means
Filed under: Potassium Questions
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You are correct in stating that the Potassium nitrate is an oxidizer. The sugar (sucrose) is the compound being oxidized. Just mixing it does not cause smoke. The mixture must be ignited.
This is very similar to the use of Potassium nitrate in gunpowder (when mixed with Charcoal and Sulfur). Black gunpowder also smokes when ignited (remember those old guns in the movies?).
The reason for the smoke is that only part of the fuel (sugar) is oxidized all the way to Carbon dioxide and Water. Some of the sugar is only partially oxidized and will be seen as a colloidal suspension of soot (carbon) in air. This is the smoke.
Nitrocellulose and other compounds have replaced black gunpowder because they are smokeless (or nearly so).
i’m sure no one on this web site will know this
You’ve answered your own question. Look up the term ‘catalyst’.
{Later}Oy, even a "Top Contributor" in Chemistry doesn’t understand a basic principle.
Unlike the "Top Contributor", you’re on the right track. The sugar burns like normal. The potassium nitrate (KNO3) is still there after the reaction is over, it remains apparently unchanged.
C12H22O11 + 12O2 => 12CO2 + 11H2O
If we were to isotopically mark all the oxygens on the KNO3, we would find after the reaction that only two-thirds of the marked oxygens remain with the KNO3 and most of the other third went off with the CO2. Why?
We have a few simultaneous reactions happening:
C (from sugar) + KNO3 => CO + KNO2
CO + KNO3 => CO2 + KNO2
2KNO2 + O2 => 2KNO3
These three reactions happen much faster than the simple burning of sugar in air without the KNO3 catalyst. This is why the burning of the sugar happens much faster with KNO3.
"Unlike other reagents that participate in the chemical reaction, a catalyst is not consumed. Thus, the catalyst may participate in multiple chemical transformations, although in practice catalysts are sometimes consumed in secondary processes."
As to why there is smoke, the combustion of sugar isn’t perfect. There are impurities in the sugar. Thermal currents from the combustion lift up some of the sugar, the by-products, and the KNO3 up into the air. This is what you see as smoke.
Potassium nitrate is also used in amateur rocket propellant, and in several fireworks such as smoke bombs, in which a mixture with sugar produces a white smoke cloud of 600 times their own volume. The ratio for smoke bombs using sucrose (powdered sugar) and potassium nitrate is 40(C12H22O11):60(KNO3). It can be used as is,or consolidated into a lump by mixing with water to make a paste and allowing to dry overnight It can also be cooked in a pan over low heat to produce the same solid effect. The balanced equation fotr this reaction is:
5 C12H22O11 + 48 KNO3 = 60 CO2 + 24 N2 + 55 H2O + 24 K2O
You will see taht there are a number of oxidation reactions taking place. I am not sure that catalysis plays any part in this.