Safety Chat: Nitric Acid Waste

aqua regia

We’re going to be taking time out of our regular blogging schedule to remind everyone about better lab safety practices. Recently at Lawrence Berkeley National Laboratory someone poured isopropanol into an acid waste container of aqua regia. Aqua regia contains nitric acid, and the reaction for those unfamiliar with nitric acid’s oxidizing power is thus,

$$ \text{C}_3\text{H}_7\text{OH} + \text{HNO}_3 \rightarrow \text{CO}_2 + \text{NO}_2 + \text{H}_2\text{O} \text{ (Good Luck Balancing This One)}$$

Due to the pressure in the waste container, the bottle blew and spewed its golden goodness throughout the room. It fractured the safety sash, and could have really hurt someone.

The lessons you should take home:

  • Get rid of strong oxidizing acid waste as you generate it.
  • Do not trust others near your waste bottles. Don’t let others add to them.
  • If you generate strong acid wastes, probably a good idea that everyone from the undergrads and lab techs to the postdocs are made aware of the incompatibility of organics and nitric acid. You can’t expect chemists to have this knowledge anymore. 🙁



  1. William Penrose says:

    When I started my first real job in 1972 with the Canadian Govt, the biology techs used to mix up a preservative. When they followed the recipe as written, measuring nitric acid and then ethanol, a big cloud of NO2 flowed all over the table. They thought this was funny and actually looked forward to the show. I had a talk with them about the effects of NO2 and convinced them to mix the reagents in a different order. I’m surprised no one was hurt over the years they’d been doing it the old way.

    Dangerous Bill

  2. Mmmm aqua regia. I don’t suppose they sent out a campus wide e-mail making fun of the offender again? Because that practice works really well and all. Hopefully nobody got hurt.

    P.S. Does anyone even remember how to balance those equations anymore? I always think of it as one of those things that you forget the moment you finish your first gen chem midterm.

  3. Noel, I think the reaction of isopropanol with aqua regia would be one hell of an exam question.

    I can tell you that EtOH and red fuming nitric acid do NOT mix either :-/ (once I made the mistake of not using a completely dry 10mL graduated cylinder, now I’ve learned).

  4. I accept your challenge!

    C3H7OH + 18HNO3 –> 3CO2 + 18NO2 + 13H2O

    It’s piss easy if you consider it as 2 ion electron half equations taking place in acidic conditions and then adding them together.

    • I got the same answer without resorting to half reactions:

      take a basis of 1C3H7OH

      balance carbon:
      coefficient of CO2 = 3

      balance nitrogen:
      coefficient of HNO3 = coefficient of NO2 call it x
      call the coefficient of H20 y

      at this point the equation looks like
      C3H7OH + X HNO3 –> 3 CO2 + X NO2 + Y H2O

      balance Oxygen:

      balance hydrogen:

      two equations two unknowns
      x = 18 y = 13

  5. Philip Badawol says:

    So Bill, they it was funny.How long did they do that for until you changed their minds?

    App.Chem Sec
    Dpt App.Sci, PNG UNITECH

  6. Philip Badawol says:

    So Bill, they it was funny.How long did they do that for until you changed their minds?

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  9. I accidently poured about 100 ml of nitric acid down my drain. The bottle broke. I have a septic tank system for grey water treatment. Will this cause a problem?
    I immediately flushed with a lot of water. Then I put some bicarb of soda down – thinking to neutralise the acid. Then read that ammonia could so poured a bottle of ammonia disinfectant down.
    Any tips or advice greatly appreciated.

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