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Name: Bob 
Status: teacher 
Grade: 9-12 
Location: MO 
Country: USA 
Date: Winter 2009-2010


Question:
I teach Hazwoper, and was reading a novel from the late 1960s that discussed a chlorine-tanker derailment, and that the response was to open a bunch of ammonia tanks to neutralize it.This somehow does not sound right, even though the author is pretty knowledgeable. All I can find on line is about the obvious "do not mix BLEACH with ammonia," but nothing about straight chlorine, vs. sodium hypochlorite. I would be interested to find out what would happen if Cl2 was mixed with NH3.



Replies:
When Chlorine gas is used for water sterilisation - as in large swimming pool complexes - Ammonia is often kept on hand to detect leaks!

Chlorine is colourless at low concentrations, but is extremely corrosive and very very very toxic - causing breathing difficulties and leads to damage of tissue in the mouth and lungs. A cheap and effective way to test for chlorine in the plant room is to take a squeezable bottle with some cloudy ammonia and puff the vapour into the air. Ammonia gas combines with chlorine to produce (among other products) Ammonium Chloride, which is a white powder. What you see are clouds that look like white smoke.

Yes. Ammonia will neutralise chlorine, but in using it to deal with a tanker spill, I imagine it would be as difficult to control the ammonia as much as the chlorine, and ammonia is also poisonous.

A more practical solution would be to cool the tanker with water which also dissolves the gas and prevents it drifting in the air. The result is mostly hydrochloric acid, which can easily be neutralised with caustic soda, or even crushed marble (sodium carbonate)

Intriguingly, the reason chlorine is used in swimming pools is not only to kill bacteria, but to neutralise the ammoniated products which result from urine in the pool!!! The smell you often detect in the evening is chloroamines - not chlorine. That smell tells you that the chlorine is doing its job!!

The main reason or not mixing bleach (Sodium Hydrochlorite) with ammonia is that it can release chlorine as a gas. VERY dangerous!

2NaOCl + 2NH3 --> 2NaONH3 + Cl2

Nigel Skelton
Tennant Creek High School
AUSTRALIA


Indeed mixing hypochlorite (bleach) and aqueous ammonia is very hazardous. The reaction products are NClx where x=1-3 These are toxic but very irritating, so unless trapped one would evacuate by necessity.

You have to be careful the use the terms: "chlorine". Does that mean Cl2 or hypochlorite? The reactions are different. Does "ammonia" mean NH3 or an aqueous solution. Those too are different reactions. The "best" of not very good options is anhydrous Cl2 and anhydrous NH3 with a minimal amount of water, which is always present. There the reaction product is NH4Cl. But even there the remediation should only be done by trained personnel.

Vince Calder



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