DEMO: Water from fire! Hydrocarbon combustion. 

This is really a shortened version of a more detailed video on combustion, which I think will answer many of your questions-- ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-eocyl9dZ7W0.html

Good point. I have the control set up in the lab my students do. I unfortunately did not think of doing it for the video. I was focused on the equation, which tells us water is forming, but of course that is not empirical.

I am still making videos, just not a lot... I have one coming out in a couple weeks on the science of the greenhouse effect.

Sir can you make a video on oxidation number in a decomposition reaction.

😊

It is pure H2O. ‘Fresh water’ usually refers to non sea water- water from Lakes and rivers and streams. This is not sea water. It is certainly potable, if that is what you are thinking of.

The only thing I can think of is getting the mass of the collected water, as opposed to retrieving it into a vessel of some sort. I would do it with a 250 or 500 mL glass graduated cylinder, inverted on top of the lit candle, to maximize the surface area on which the water can condense, and minimize the heating of the top of the glass since heated glass would decrease the amount of water condensing on it. You can weigh the cylinder before and after to get the water mass. You will still have uncondensed water vapor but I think it would be fairly minimal once the candle goes out if there is enough surface area for the water to condense on to, and it does not heat up much. It would be nice to check the results via stoichiometry however it would be difficult to distinguish between the mass of burned wax versus mass of burned wick (cellulose), as well as the wax formula itself being variable. However the wick likely contributes only a small fraction of the water vapor so if you just did stoichiometry with wax and assume a formula of C24H50-- it would probably be pretty close. A before/after weighing of the candle would enable you to non-stoichiometrically approximate the mass of water + CO2 produced, and so the subtracting out the mass of collected water would also give the mass of CO2, which of course could also be checked stoichiometrically.