I have a bottle with an unknown acid which is H2SO4 or HBr. How can i check which one it is? I tried to put two copper electrodes in a small sample of
the solution and connected them to a battery. I saw some pink/purple color forming but don't know if it is because the acid attacks copper.OneEyedPyro - 14-4-2016 at 07:45
One easy way to tell would be by heating a small sample, HBr would boil away rather quickly while a H₂SO₄ should take much longer to boil away
completely. Sulfuric acid typically has little to no smell either while even a fairly weak HBr solution should have a sharp scent similar to HCl.MrHomeScientist - 14-4-2016 at 07:54
Do the standard test for sulfate by adding a soluble barium or calcium compound. If a white precipitate is seen, it's sulfuric acid.MrMario - 14-4-2016 at 08:01
Thanks for the fast help. I added some HCl to form Elemental Bromine again but not even the slightest color change occured, so i guess it's Sulphuric
acid.ParadoxChem126 - 14-4-2016 at 08:37
HCl will not react with hydrobromic acid to produce elemental bromine. Bromine should, however, be released in an oxidizing environment. It may
produce a color change in contact with aqueous hydrogen peroxide, but stronger oxidizing agents (e.g. potassium permanganate) would produce more
significant quantities of bromine. MrHomeScientist's sulfate test is probably the most practical (and safest) option here.MrMario - 14-4-2016 at 08:44
[Edited on 14-4-2016 by MrMario]Darkstar - 14-4-2016 at 08:48
I think he meant he added HCl to the sample that he had the electrodes in, which would have created some hypobromite if it were HBr.DraconicAcid - 14-4-2016 at 08:50
Add a drop to a solution of silver nitrate. Silver bromide will precipitate; silver sulphate will not.
Add some to some copper oxide. If it dissolves to give blue, it's sulphuric. If it dissolves to give purple or brown, it's hydrobromic.Nucleophile - 14-4-2016 at 12:52
@MrMario
Just add the acid to some Calcium chloride. If it is H2SO4, CaSO4 is going to precipitate out. Calcium bromide is very soluble. JJay - 14-4-2016 at 12:55
Hmmm... Does anyone know what is happening here? It seems rather unlikely that HCl can oxidize the bromide back to bromine. MrMario - 15-4-2016 at 03:52
I put some CaCl2 solution with the unknown acid in a beaker and nothing visible happened.
Now i'm not 100% sure if it's HCl or HBr so I put two copper elektrodes again in the solution.
H2 gas was produced and the solution became yellowish + some slightly yellow powder at the electrode.
Since AgNO3 is not avaible and would in both situations (AgCl/AgBr) produce a percipitate i don't know how i could else test it.
Here are some pictures of the electrolysis of the solution: ave369 - 15-4-2016 at 04:30
By smell, godsdammit! H2SO4 has no smell. HBr has a smell.DJF90 - 15-4-2016 at 04:36
I advise the OP to find a decent text on qualitative inorganic analysis.MrMario - 15-4-2016 at 06:52
