Hydrochloric Acid with "Coloring Agents"

[TranslucentDragon]

I was wondering if instead of using the normal chlorides to turn fire into different colors (strontium chloride, barium chloride, copper chloride, etc) if you could mix strong hydrochloric acid with a "coloring agent", such as copper oxide, and spray that solution into a fire to change its color. Is this possible? and if so, would the reaction be endothermic or exothermic (specifically exothermic, because I would put the solution into a plastic bottle if the heat wouldn't cause it to meant).

 

I ask mainly to make sure that this won't blow up and that if this is possible, if it is safe enough for me to do. I rather die (with all my limbs attached) due to old age than from being stupid.

 

Thanks all,

-TD

[Gunzway]

Well, depending on the colouring agent you use, you'll probably end up making a chloride of that salt anyway. Like in the example you gave:

 

CuO(s) + 2HCl(aq) ---> CuCl₂(aq) + H₂O(l)

 

You'll get copper (II) chloride if you used copper (II) oxide. Then whatever you had in excess, either HCl or your salt would be left and you would be spraying that into the flame as well. So it is essentially the same as spraying dissolved chloride salts anyway. Except it probably wouldn't work very well since they normally dissolve the salts in ethanol or methanol so the salt can be excited more easily when it hits the flame. But if you added a small sample of the salt onto platinum/nichrome wire and held it into the flame, that would be fine. Spraying would need the alcohol as the solvent for it to be impressive.

 

Reaction would be exothermic, but nothing chaotic if in reasonable quantities. I would recommend performing the reaction in a beaker of some sort and safety glasses. I would personally just make the chloride salts of the metals you want to test and recrystallize so they are crystalline and go from there.

[TranslucentDragon]

Sounds good. How would I recrystalize them? And how can you tell if the reaction is exothermic?

[Gunzway]

If I were doing it, I would use an excess of CuO and react the HCl with it in a beaker, stir and leave over-night. I don't like hydrogen chloride gas and since copper oxide is insoluble, I would do it this way. Decant and filter the solution which is going to be very concentrated and either boil excess water out and filter or just let it evaporate with either sun/desiccator. I personally prefer desiccant but it's up to you. Lots of information online on all of this.

 

As far as I know, you can't really tell from the equation alone. I just know the general rule that acid + metal oxide reactions are going to be exothermic, partly because they are essentially a neutralisation reaction of an acid and a base (metallic oxides are basic, non-metallic oxides are acidic).

 

It is however all truly to do with enthalpy, and you could look up enthalpies of the reactants and products and use Hess's law to work it out. Doing it that way involves using a table which is fine for an exam but since you're using the internet it's easier to just search the answer up. There is another way to predict by comparing pi and sigma bonds in reactants vs products. It's easier to experimentally work it out in a controlled environment with a thermometer before a scaled up synthesis for most cases.