In the chemistry lab, I stupidly decided to mix hydrochloric acid and sulphuric acid, both concentrated, in a random ratio, which was about $\pu{50 ml}$.

When I poured them in one test tube, the result was a vigorous reaction, with the green coloured liquid mixture "jumping" in the test tube and a white gas being released.

Could someone tell me what the resultant chemicals were?

  • $\begingroup$ Are you sure nothing else was in the test tube? $\endgroup$
    – MollyCooL
    Mar 27, 2018 at 12:38
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    $\begingroup$ Did you add the sulfuric acid to the hydrochloric acid, or the reverse? Hydrochloric acid stock solution is already about 63% water, so I would expect fewer side effects from adding sulfuric acid to hydrochloric. $\endgroup$ Mar 27, 2018 at 12:59
  • $\begingroup$ quora.com/What-happens-when-we-add-HCl-to-H2SO4 might help but I need to get more sources $\endgroup$ Mar 27, 2018 at 13:17
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    $\begingroup$ Basically, if you pour $\ce{HCl}$ onto $\ce{H2SO4}$, hydrogen chloride gas will be emitted simply because $\ce{H2SO4}$ has a strong affinity for the water the hydrogen chloride is dissolved in. $\endgroup$ Mar 27, 2018 at 13:21
  • $\begingroup$ @Molly The testube was clean.Well ,I added H2SO4 first and then added the HCl.The resultant liquid was slighly lighter than the HCl colour and loads of the white fumes was emmited,though the reactants were small in quantity.Even with the ventilator fans on,the gas pretty much covered the room. $\endgroup$ Mar 27, 2018 at 14:19

2 Answers 2


Three things occurred. First, sulfuric acid as an high affinity for water (it is indeed used as a drying agent in some cases. For instance, if you wanted pure and anhydrous bromine, you could bubble wet bromine gas in concentrated sulfuric acid). So, one thing is the "stealing" of water by sulfuric acid, which took the solution one step forward the saturation point (with the release of gas).

The release of gas was aided by the exothermic reaction of sulfuric acid with water: (self) heating of the solution helped releasing the gas.

Edit: the following is an hypothesis, made by assuming that the "extreme" reaction conditions could have aided an unlikely redox reaction, but I am not sure about the oxidation of HCl:

And finally, sulfuric acid is a oxidizing acid: it oxidized part of the hydrochloric acid to chlorine, which made the solution green (which probably was released as a gas, together with HCl).

  • $\begingroup$ Does the release of Chlorine gas makes the solution green? I know the colour of it, is green. $\endgroup$
    – MollyCooL
    Mar 27, 2018 at 14:24
  • $\begingroup$ Not the release of chlorine, but the presence of chlorine in solution! When I was talking about the release of chlorine I was describing the composition of the gas, which probably contained part of the chlorine generated. Oh, and it contained water vapor, probably (if the temperature was high enough, as I suspect) $\endgroup$
    – user32223
    Mar 27, 2018 at 14:27
  • $\begingroup$ The resultant was medium light green in colur,so the Clorine gas if formed,could'nt have dissolved in the solution. $\endgroup$ Mar 27, 2018 at 14:28
  • $\begingroup$ What colour do you see when you put a droplet of red wine in a large glass of water? $\endgroup$
    – user32223
    Mar 27, 2018 at 14:31
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    $\begingroup$ Are you sure sulfuric acid is oxidizing enough to oxidize chloride ions? I can't find the redox potential, but I do know that in the lab we prepare gaseous hydrogen chloride by dripping concentrated sulfuric acid into sodium chloride, and I've never seen any oxidation of our reagents from any chlorine gas that might form. $\endgroup$
    – ralk912
    Mar 27, 2018 at 22:45

Sulfuric acid occupies several categories besides corrosive, one of which is as a dehydrant. The water removed from hydrochloric acid produce a vapour of hydrogen chloride. The solution is effervescent. There should not be a green colour unless the test tube was contaminated. I was hoping that you had done this in a fume hood.

I did this using 10 ml of each acid knowing what to expect. The fumes actually escaped as I shut the sash quickly causing turbulence. The fumes were quickly detected. If this were done in a prep room without a fume hood, with larger quantities you would be lucky to walk away from this! Despite their being stored together, they are not compatible.


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