Sciencemadness Discussion Board

Leaky Joints

196 - 3-11-2015 at 15:16

Today I was making some nitric acid with sulfuric acid and potassium nitrate. I know it's been done a lot on the Internet before, but in the middle of the distillation some nitric acid vapors and nitrogen oxides started leaking out of the joint between the 75 degree adapter and the condenser, and to a lesser extent the joint at the reaction flask and the bottom of the adapter.

As still somewhat of a beginner in amateur chemistry work, I was just wondering what you all thought may have caused the leaking. This was my first time using some Chinese glass I'd gotten off eBay, though the seals initially seemed reasonably tight, at least at the joints that were leaking. I also greased the joints with some sulfuric acid although it didn't seem to stop the vapors from seeping through and escaping.

Thanks.

Detonationology - 3-11-2015 at 15:49

I too purchased some glassware from China from 2 different suppliers. Simply put, the so called Standard Taper was not up to standard. There was a a very loose fit towards the bottom of the taper. Did you use keck clips to secure the joints? A high-temp grease made by Corning solves most leak issues, and it's fairly inert. I've also heard of someone who purchased glassware with "unfrosted" joints, but I have never stumbled upon one without the frosting. Also, a vacuum pump or aspirator can be used to seal the joints and pull off the nasty NOx fumes.


[Edited on 11-4-2015 by Detonationology]

Agari - 3-11-2015 at 16:50

Dow Corning High-Vacuum grease does the job for me and is in fact relatively inert, as I did not get any noticeable contamination when performing chemistry experiments.

Unrelated: Does anybody know what hydrogen fluoride smells like,or is it odorless?

[Edited on 4-11-2015 by Agari]

hissingnoise - 4-11-2015 at 01:33

Plumber's teflon tape is effective too, and cheaper than HV grease . . . ?

JJay - 4-11-2015 at 01:41

I don't know what it smells like, but I highly doubt that hydrogen fluoride is odorless.

arkoma - 4-11-2015 at 01:49

Quote: Originally posted by hissingnoise  
Plumber's teflon tape is effective too, and cheaper than HV grease . . . ?



Used PTFE tape myself. Works great.

szuko03 - 4-11-2015 at 07:27

I am all for that tape. I just experienced it the for the first time today and it is definitely made for this type of application.

Deathunter88 - 4-11-2015 at 08:01

Just FYI, glassware in China 24/29, not 24/40. Don't know about how much of a difference that makes.

Amos - 4-11-2015 at 08:46

Quote: Originally posted by Agari  

Unrelated: Does anybody know what hydrogen fluoride smells like,or is it odorless?


Weird thread to ask this in, but I've smelled it before and it's similar to hydrogen chloride but more biting and unpleasant.

Agari - 4-11-2015 at 17:14

Quote: Originally posted by Amos  
Quote: Originally posted by Agari  

Unrelated: Does anybody know what hydrogen fluoride smells like,or is it odorless?


Weird thread to ask this in, but I've smelled it before and it's similar to hydrogen chloride but more biting and unpleasant.


What were you doing that exposed you to a sufficient concentration of HF that you could smell it?
Edit:Is HF gas also rapidly absorbed through the skin like its aqueous form?

[Edited on 5-11-2015 by Agari]

Agari - 4-11-2015 at 17:16

Quote: Originally posted by JJay  
I don't know what it smells like, but I highly doubt that hydrogen fluoride is odorless.


You never know,maybe it causes rapid olfactory fatigue like hydrogen sulfide.
Nevermind, Amos already provided an answer.

Agari - 4-11-2015 at 17:20

Quote: Originally posted by szuko03  
I am all for that tape. I just experienced it the for the first time today and it is definitely made for this type of application.


Never tried teflon tape,but seeing as a large amount of stir bars are coated in teflon to prevent reaction(And mostly do not receive damage unless used with liquid alkali metals),I would assume that it would work.

Upsilon - 4-11-2015 at 17:41

Quote: Originally posted by Agari  
[You never know,maybe it causes rapid olfactory fatigue like hydrogen sulfide.


This only happens at higher concentrations of H2S. You can consistently keep smelling it at low concentrations without a health risk. While some sources say that this deadening of sense of smell makes it very hazardous, I see it as a benefit - you know when you stop smelling it that you need to GTFO fast.

Agari - 4-11-2015 at 17:49

Quote: Originally posted by Upsilon  
Quote: Originally posted by Agari  
[You never know,maybe it causes rapid olfactory fatigue like hydrogen sulfide.


This only happens at higher concentrations of H2S. You can consistently keep smelling it at low concentrations without a health risk. While some sources say that this deadening of sense of smell makes it very hazardous, I see it as a benefit - you know when you stop smelling it that you need to GTFO fast.


That is true,but when we don't smell something,we generally do not think about it and it is easy to forget that a toxic gas is present in the atmosphere unless you smell it or keep constantly reminding yourself that you are working with hydrogen sulfide.