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Fire Water Answered


I am doing an experiment called Fire Water for my chemistry class in a couple weeks. I've been trying to find a chemical equation for this so I can better explain the combustion reaction that is occurring. Does anyone have an equation? Also, I've been trying to figure out what the diethyl ether does, so that the potassium catches fire rather than fizzing away. If anyone has any solutions, they would be much appreciated. Thanks!

The reaction that I'll be performing:


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Jack A Lopez
Jack A Lopez

Best Answer 1 year ago

Um, here is a guess:

Potassium metal, in an exchange reaction with water, makes KOH and H2 gas, and heat.

K(s) + H2O(l) = KOH(aq) + 0.5 H2(g)

Potassium metal melts (into puddle on water surface). Potassium metal has a low melting point (63.5 C), and it is less dense than water (0.828 g/cm^3, liquid at its MP)

K(s) = K(l)

Some of the potassium metal catches fire and combusts with O2 from the air.

2 K(l) + 0.5 O2(g) = K2O(s)

Potassium oxide reacts with water to make the hydroxide.

K2O(s) + H2O = 2 KOH(s)

KOH, a product from two of the above reactions, dissolves readily in hot water.

2 KOH = 2 K+(aq) + 2 OH-(aq)

Also the diethy ether is boiling too. It has a low boiling point (34.6 C).

(C4 H10 O)(l) = (C4 H10 O)(g)

The diethyl ether catches on fire too, and combusts with O2 from the air.

1 (C4 H10 O)(g) + 4 O2(g) = 4 CO2(g) + 5 H2O(g)

The hydrogen gas, made in the first reaction, is likely burning too.

H2(g) + 0.5 O2(g) = H2O(g)

I think most of the chemical reactions I have listed so far are exothermic, releasing heat, which uh, explains why everything is on fire.

The exceptions are those physical reactions involving melting a solid, or boiling a liquid. Those are endothermic, absorbing heat from their surroundings.

Finally, some small fraction of the potassium metal is getting vaporized, and excited. What is symbol for atom in excited state? Maybe a star superscript?

K*(gas,excited) = K(gas, ground state) + photon

and, that is kind of the hand waving explanation, for where the pretty color in the flames comes from.


Reply 11 months ago

Thank you! I used some of this information in my explanation while I performed the experiment!


Best Answer 1 year ago

It is written in the very videodescription you posted:
NOTE FROM THE PROFESSOR: This reaction is the same as that of K with water, 2K + 2H2O → 2KOH + H2. The difference is that diethyl ether floats on the surface of the water (it's less dense) and it has a very low boiling point so it's vapour easily catches fire to form CO2 and more H2O. Once it's burning, some of the K is vapourized and gives the flame a lilac colour.


Reply 11 months ago

Thank you very much! With your help, I was able to complete my reaction successfully for my class!

Jack A Lopez
Jack A Lopez

1 year ago

By the way, there is a longer version of this video, with two chemistry professors in it, explaining what is going on.

Erm, actually only one of these two professors, does all the talking. It is sort of the same style as Penn and Teller, if you have ever seen those guys. One talks constantly. The other is completely mute. And the audience is left wondering, which one is the brains of the partnership.