Expert: George Maxwell - 12/18/2007

Question
I'm sure a lot of people have heard of the idea that mixing ammonia and bleach produces deadly gases.  I was wondering if you can elaborate on that and possibly explain what is actually happening chemically when the two chemicals come into contact.  Thank you so much!

Answer
Hi, and thank you very much for your question; apologies for the delay in answering.

It's never a good idea to mix bleach with anything, as it will decompose to form chlorine gas in contact with acids. However, the case of bleach and ammonia is slightly different; there are two key dangerous reactions that may occur.

Note:
NH3 =Ammonia
HCl = Hydrochloric acid
NaOCl = Sodium Hypochlorite (bleach)
Cl = Chlorine

1) The bleach can decompose to form hydrochloric acid. Reaction of hydrochloric acid with ammonia will form toxic chloramine fumes:

a) Formation of Hydrochloric Acid
NaOCl -> NaOH + HOCl
HOCl -> HCl + O
b) Fomation of Chloramines
NaOCl + 2HCl -> Cl2 + NaCl + H2O
2NH3 + Cl2 -> 2NH2Cl (chloramine).

2) In an excess of ammonia, the explosive and toxic liquid hydrazine can be formed. In pure form, this substance can explode vioently (and was actually used as a rocket fuel); in impure form, the mixture is likely to boil and throw hot liquid about: -note N2H4 = Hydrazine

2NH3 + NaOCl -----> N2H4 + NaCl + H2O

In any case, it's difficult to predict which reaction will happen in a domestic situation, so in the case of accidental mixing of cleaners, the fire service will attend with full chemical protection gear and the local hospital will put special plans in to action for the treatment of contaminated patients.

Hope this information helps.