HCl + NH4OH Reaction

HCl + NH4OH Reaction: Hi, could you please advise me about a demo of HCl and NH4OH fumes mixing? Is it safe enough to put 30 ml (or less?) of each into separate petri dishes in the fume hood?  Can the fume hood be turned off for 10 seconds for better visibility of the NH4Cl and then turned back on again?

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Publication Date: 26 August 2016
Asked By: Karen Cox
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HCl + NH4OH Reaction

We understand that you are trying to demonstrate the diffusion of the two gases, which react when they come together to form solid ammonium chloride. The concentrated solutions of HCl and NH4OH are both corrosive and should be handled in an operating fume cupboard.

Many models of fume cupboards have a purge system that keeps the fan running after it has been switched off to allow any residual hazardous vapours/fumes in the cupboard to be removed. Therefore, it may not be possible to turn off the fume cupboard for 10 seconds. In addition, we are not sure for your procedure whether 10 seconds would be sufficient time to see the reaction, even if you were able to turn off the fan in the fume cupboard.

Alternate method: We recommend an alternative way of demonstrating this reaction see: http://www.rsc.org/learn-chemistry/resource/res00000682/diffusion-of-gases-ammonia-and-hydrogen-chloride?cmpid=CMP00005016

The concentrated corrosive solutions will still need to be handled wearing appropriate PPE (lab coat, closed-in shoes, safety glasses and nitrile gloves) and in an operating fume cupboard, but due to the reaction being contained in a closed vessel, it can be taken out of the fume cupboard to show students. Another benefit is that smaller quantities of the concentrated solutions can be used. Cleaning up should be conducted in the fume cupboard: the cotton buds/balls can be placed in a beaker of water to dilute the reagents before disposal and the tube can also be rinsed using water.


'Diffusion of gases - ammonia and hydrogen chloride', Royal Society of Chemistry website. http://www.rsc.org/learn-chemistry/resource/res00000682/diffusion-of-gases-ammonia-and-hydrogen-chloride?cmpid=CMP00005016. October 2015.

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