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The most common formula for smoke grenades and sugar rocket fuel is $60\%\ \ce{KNO3}$ (potassium nitrate) and $40\%\ \ce{C12H22O11}$ (sugar). This is a 3:2 ratio, but I've also seen 2:1 and 5:3 with similar results.

The formulas I've seen (https://www.scienceforums.net/topic/19364-kno3-and-sugar-smoke-bomb/) are: $\ce{5C12H22O11 + 48KNO3 -> 24K2CO3 + 36CO2 + 55H2O + 24N2}$ and $\ce{C12H22O11 + 24KNO3 -> 24KNO2 + 12CO2 + 11H2O}$.

Based on the first formula, using mole ratios and molar masses, it would be ideal to have $\pu{68.5 g} \;(\pu{0.2 mol})$ of sugar mixed with $\pu{194.1 g} \;(\pu{1.92 mol})$ of oxidizer. This is not even close to the advertised 3:2 ratio, being a 17:6 ratio.

Question 1: Why do you need substantially less potassium nitrate than as indicated by the chemical equation?

Now, in terms of the smoke grenade, an alternate formula I've seen used involves potassium chlorate (oxidizer) and lactose (same as sucrose). This, from what I've read, burns at a lower temperature and can produce colored smoke.

Question 2: Which one produces more smoke than the other (and why)?

Question 3: How can I modify the $\ce{KNO3}$ formula to produce more smoke. Which reactant produces the smoke? Fuel (sucrose/lactose) or oxidizer (K-nitrate/K-chlorate)? From a 60:40 ratio, should I add more sugar to make it like a 40:60 ratio, or more potassium nitrate, therefore 70:30 is better?

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  • $\begingroup$ I'm not sure the reaction is correct, I've found another source with the following reaction: $\ce{2KNO3(s) + CH2O(s) → 2KNO2(s) + CO2(g) + H2O(g)}$, $\ce{CH2O}$ being an empirical formula for glucose, which is actually $\ce{6 x CH2O}$. The ratio would still be off (about 6:1), not sure why. Maybe the recipes simply work with an excess of sugar? $\endgroup$ – IanC Jun 15 at 20:34
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    $\begingroup$ Well, if there was no air there and you you didn't want any, well, smoke, then putting that much oxidiser would be proper. $\endgroup$ – Mithoron Jun 15 at 21:21
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    $\begingroup$ @Mithoron Are you saying that more sugar would release more smoke? I kinda figured that because smoke comes from incomplete combustion, by piling on more organic stuff, more smoke would appear. $\endgroup$ – Christopher Marley Jun 15 at 21:57
  • $\begingroup$ Either you want smoke or a complete reaction. $\endgroup$ – Alchimista Jun 16 at 8:55

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