July 23, 2019, 11:56:35 AM
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Topic: firework colours  (Read 676 times)

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Offline zebjonk

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firework colours
« on: January 24, 2019, 05:56:39 AM »
in my chemistry class we need to figure out why some things like copper sulfate make a flame go blue/green. i can't find a site as to why this is. if you could a) be so kind to post a link to a site that explains it, or b) explain it in the comments, that be amazing.

and we need to make an equation for said fireworks, it has to be for the pretty kind (not english, sorry). i haven't started on it yet, so if you could help me with it that'd be awesome

Offline Enthalpy

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Re: firework colours
« Reply #1 on: January 24, 2019, 06:10:35 AM »
Welcome, zebjonk!

Maybe you could start at Wiki
https://en.wikipedia.org/wiki/Flame_test

Don't expect simple explanations, because the metals emit several wavelength, and the way our eyes combine them into one colour is complicated.

An equation that relates what to what?

Offline zebjonk

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Re: firework colours
« Reply #2 on: January 24, 2019, 06:53:05 AM »
my bad
like an equation like
...CO2 +...Mg = ...c + ...MgO

Offline Enthalpy

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Re: firework colours
« Reply #3 on: January 25, 2019, 12:23:16 PM »
To my understanding and according to Wiki's explanations, the coloured light is emitted by lone metal atoms in the flame. It's the reason why the colour lets identify the metal independently of the compounds it makes.

So there is no chemical reaction to write for it. Just gaseous Cu atoms for instance, which are released in an excited state because a flame is a violent reaction, and these atoms emit light as they change to a state not or less excited. Other processes exist for other elements, where molecules and radicals can emit most light, for instance OH, CO2 or solid C.

Metals are more efficient than other elements to colour a flame. The minuscule vapour amount of a solid grain of NaCl hold in a hydrocarbon flame suffices to give the flame the Na colour. The reason of this efficiency isn't perfectly clear to me, but it makes the flame test a means to identify the metals.

Atoms of each element can radiate a limited series of wavelengths that characterizes that element. This series can't be computed by hand from the filling of the electron shells. Also, only some wavelengths are visible, and which ones are depends on the metal. Finally, our eyes analyse colours with red, green and blue bands only, and we reconstruct more colours from only three intensities and depending on our culture. As a result, the flame colour of each metal should be understood as experimental data, whose justification works but needs lengthy software modelling.

Offline zebjonk

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Re: firework colours
« Reply #4 on: January 28, 2019, 06:47:30 AM »
thank you very much, using this and the wiki link you sent me i got a b+!
i still find it pretty interesting, so could you tell me how this equation works if we don't look at the colours but look at the composition and how it changes when the fireworks explode?

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