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Author: Subject: Whistling Reaction Apparatus
bfesser
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[*] posted on 11-8-2009 at 17:07
Whistling Reaction Apparatus


So, I'm wondering if anyone can suggest what caused an apparatus I used today to whistle/whine.

The apparatus consisted of an all glass HCl gas generator connected to a fritted glass bubbler with a short piece of natural latex rubber tubing. The bubbler was filled with distilled water, and lowered into an ice bath. The reaction flask was charged with sodium chloride and the addition funnel with sulfuric acid. When the acid was allowed into the reaction flask slowly, foaming occured, and gas bubbled through the fritted tube in the bubbler.
After a while, the gas evolution in the reaction flask continued, but bubbles weren't appearing in the bubbler. It was noticed, however that the bubbler was producing a high pitched whistling/whining noise. It varied in pitch and continuity, and even made some interesting melodies. I was sure that the hydrogen chloride was dissolving, because refraction could be seen from concentration gradients in the solution.
The short piece of latex rubber tubing became brown in the middle, where it was exposed to HCl, but remained a light yellow to amber on the ends where the glass tubing was inserted. The tubing reeks of 'rotten eggs' now.

Now for my questions:
What reaction occurred in the tubing, causing the discoloration?
What was the 'insoluble' (less soluble than HCl, at least!) gas generated in this reaction?
What caused my bubbler to make music? :P

(My best guess is the collapse of microscopic bubbles within the frit as gas was absorbed into solution caused some gas to be 'swished' back and forth within the frit, causing a whistling effect.)

[Edited on 8/13/09 by bfesser]
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[*] posted on 11-8-2009 at 17:38


Cavitation? That HCl is dissolving damned fast, after all it would like to suck back into the fritted glass if it could.

Did it have the same sort of sound as a pot of water nearing boiling?

Tim




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[*] posted on 11-8-2009 at 17:43


I suppose it could have had the same sort of sound. It was difficult to hear, as I had several fans and the faucet running for ventilation and excess gas absorbtion. At first I thought my ears were just ringing.
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[*] posted on 11-8-2009 at 18:38


Quote: Originally posted by bfesser  

My best guess is the collapse of microscopic bubbles within the frit as gas was absorbed into solution caused some gas to be 'swished' back and forth within the frit, causing a whistling effect.

That would be the most logical explanation. Microscopic bubbles form, but immediately collapse again, making a "click" every time they collapse. A few hundred or thousands of clicks per second equal a whistle.
It's similar to cavitation, but without actual boiling.

A frit is actually quite a good way to prevent suckback, provided that the gas stream doesn't stop.

I once had the same "sound generation by gas absorption" effect when I was disposing of a large amount of gaseous ammonia (from a reaction in liquid ammonia as the ammonia had to be evaporated at the end, and I didn't want to lose it) by bubbling it into water using a glass pipette.
Since the gas stream was very brisk, the sound was a low-pitched rumble/roar (similar to a powerful water boiler) instead of a whine. The water also got hot very quickly from the absorption heat.




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[*] posted on 12-8-2009 at 15:27


Is this a test? Most rubber tubing has stabilizers in it that don't hold up under attack from HCl. You didn't say how you are generating HCl. NaCl/H2SO4 is one method. NaCl + HCl (aq)/ H2SO4 is another. There are others. Do you think you could be generating some H2? What is the evidence there is a less soluble gas fraction present? The noise question was trivial and a number of reasonable speculations have been posted. Why are you making aqueous HCl? It's cheap and available to anyone! We usually make HCl gas when want to crystallize an organic base.

[Edited on 12-8-2009 by chemrox]




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[*] posted on 12-8-2009 at 17:06


A bit hostile? I was making it because at the moment I don't have much else to do, and I -enjoy- doing chemistry. So, what your saying is, in effect, unless someone discovers a new subatomic particle, they shouldn't post here? I thought the noise was an interesting effect, so I thought I'd get some feedback. What's your problem?

The reaction was with AR grade concentrated sulfuric acid and ACS grade sodium chloride. I do not believe that I was generating hydrogen gas.

I guess I forgot to mention that an insoluble gas (possibly had reached saturation of this gas) was also observed. Possibly sulfur dioxide or hydrogen sulfide?
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[*] posted on 12-8-2009 at 17:22


Quote: Originally posted by bfesser  


I guess I forgot to mention that an insoluble gas (possibly had reached saturation of this gas) was also observed. Possibly sulfur dioxide or hydrogen sulfide?


A lot of rubber tubing does contain sulfur compounds, and the rotten egg smell is sure suggestive.

But SO2 or H2S would probably have dissolved, wouldn't they? I guess either would be less soluble in the HCl (aq) you made. I think the sound effects are more interesting however.
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[*] posted on 12-8-2009 at 19:01


I think the sulfur question is easy: Sulfur is used to vulcanize rubber, especially natural rubber, as used in latex tubing.

The bubbles that didn't dissolve, at first: Could they just be air that you pushed out of the system at startup?

I have heard cavitation with improperly operated/placed large pumps. It sounds like gravel going through the pump. I can't think of a better theory for the noise than collapsing bubbles or sucking HCl gas, however.




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