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My chemistry teacher taught us that one of the ways to see if we had produced ammonia gas in a reaction was if it released a pungent smell (Even BBC supported that here! http://www.bbc.co.uk/schools/gcsebitesize/science/triple_edexcel/qualitative_analysis/qualitative_analysis/revision/3/ ). However, as far as I knew, Ammonia was poisonous. Is it okay to breathe in small amounts of Ammonia, or is this a hazardous practice that can potentially harm us?

This question What chemical compounds used in qualitative chemistry can be distinguished by smell? did say that Ammonia could harm you, but it doesn't say how much is needed to cause the damage, which is a big part of my question.

Thanks!

Community
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N A
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    Yes, large amounts of ammonia are poisonous. However ammonia is a common household cleaner. Very small amounts are ok. Your teacher should have taught you the technique to use the smell test too. You don't stick a nostril over the test tube and deeply inhale, but rather fan the top of the tube with your hand towards your nose to just get a whiff. – MaxW Feb 15 '16 at 16:22

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First, using the smell test for chemistry is dangerous - don't do it!

Second, for this an similar questions, consult a Safety Data Sheet (ex-MSDS) for exposure limits.

The copy that I looked at indicates:

TWA of 25ppm (from the ACGIH) or 50ppm (OSHA) -- these are based on a 8 hour/day, 40 hour/week exposure.

STEL of 35ppm (short term exposure limit). Exceeding the STEL may result in 'upper respiratory tract irritation, eye damage'.

Now, the yield from your lab bench chemistry experiment is unlikely to be very high, and as you may have noticed ammonia is very noticeable (although of the several SDSs that I consulted, none list an odor thershold, surprisingly).

But, the bottom line is, do not inhale your chemistry experiments.

Jon Custer
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    This answer is an overreaction. The smell test is fine as a conformation for certain chemicals. Ammonia is sold as a common household cleaner. If getting a whiff was deadly there would be dead folks dropping like flies. Obviously the smell test isn't something that you'd use for nerve gas. – MaxW Feb 15 '16 at 18:02
  • That, of course, depends on the scale of your experiment/bath/whatnot. It is quite likely that his particular case is not deadly. But, it is not made clear if this is a small test tube, or a 30 liter bucket - I've seen 'simple' scale ups result in really bad outcomes involving rescue folks in SCBA. Getting in to the habit of sniffing, particularly without checking an SDS, is a really dumb idea. And, yes, people do drop dead from mixing common household chemicals. And, yes, ammonia could certainly trigger an asthma attack. Use your smell for cooking, not chemistry. – Jon Custer Feb 15 '16 at 23:11
  • @JonCuster: If a reaction emits dangerous sufficiently dangerous gases that breathing apparatus is required, removing the apparatus to sniff the gases would obviously be a bad idea. If breathing apparatus would not be required, however, I don't think sniffing is any more dangerous than breathing in fumes without trying to sniff them. – supercat Feb 16 '16 at 00:44
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    And there is a reason we use fume hoods for real work. Look, I would rather tell people to do things the right way rather than telling random folks with unknown facilities and safety support to go around sniffing their chemistry experiments. Much of the time it might work out OK. Some times it won't and people get hurt or killed. In the real world, in real labs, folks get hurt. – Jon Custer Feb 16 '16 at 01:15
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I would advise against placing any importance on smell as a test.

  1. Just because you smell ammonia doesn't mean it's necessarily ammonia. If humans had such a great sense of smell, we wouldn't need NMR and all those fancy machines, we would just confirm our products by their smells. Identifying chemicals by smell and taste is something that you would do a century ago and certainly not in (CURRENT YEAR).

  2. As you progress in your study of chemistry, you will make more and more dangerous compounds which obviously preclude using smell as a test. For goodness' sake, don't do $\ce{[Mo(CO)6] + 3py -> [Mo(CO)3(py)3] + 3CO}$ and try to smell the reaction to tell when it's done. (Not that you would be able to tell anyway!)

Essentially, if you're making ammonia by heating some ammonium salt, please make sure that it also turns damp red litmus paper blue. I know that in some syllabuses you will be required to write "a colourless, pungent gas was evolved" whenever you heat some ammonium salt. If you have to, by all means, write it. Just don't place so much weight on it in your mind.

Safety-wise, if it was going to kill you, it wouldn't be done in a high school lab. You are not going to die if you sniff some ammonia in a high school lab, unless you continuously and voluntarily breathe it in. You'd also have to be either pretty stupid or masochistic to do so, since it stinks.

With that said, the smartest thing to do is to avoid smelling or tasting any of your chemistry experiments. Things that can be smelled or tasted without harm are the exceptions, not the norm.

orthocresol
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  • Thank you. We do also use the litmus test for it. I knew it was not going to kill me, but I was mainly wondering if it was a violation of lab safety rules. It looked like a widespread practice, but it seemed kind of illogical to me. – N A Feb 16 '16 at 02:18
  • "[I]f it was going to kill you, it wouldn't be done in a high school lab"? Never underestimate the ingenuity of high school students! – SQB Feb 16 '16 at 06:46