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Author: Subject: The short questions thread (2)
densest
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[*] posted on 4-2-2010 at 14:14


Perhaps this should be under "Acquisition"... if so, I'll redirect this.

Is P2O5 (phosphorous pentoxide, really P4O10) a suspect reagent in the USA? It's awfully useful for thoroughly removing H2O....

I haven't seen it on any lists, but that isn't necessarily good enough to go buy 500g of something.
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[*] posted on 14-2-2010 at 11:02


I wanted to further my Lithium complex thread but due to heavy snow I dont have access to the Ammonium nitrate or the money for it either so I made some Ammonium Chloride from the materials I had on hand.

I slightly over acidified the solution of Ammonium hydroxide and Muratic acid and I want to remove this excess HCl from the crystals else they will screw with my calculations for freeing the NH3 and waste my NaOH on top of that.

I have no acetone which would be my solvent of choice to wash the ammonium chloride so I was woundering about other things like EtOH or if a simple cold water wash would be enough to remove the excess acid.


I recrystalised it using plain old H2O but there is still a little excess acid I want to remove.





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[*] posted on 14-2-2010 at 11:36


Quote: Originally posted by Sedit  
I recrystalised it using plain old H2O but there is still a little excess acid I want to remove.


Are you sure?




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[*] posted on 14-2-2010 at 15:37


Sedit, what S.C. Wack is probably trying to tell you (my guess on why he asks) is that you can not judge the presence of residues of HCl in ammonium chloride using something like a litmus paper (just my guess of what you did) because ammonium chloride is an acid itself. You would get an acidic reaction even if there is no HCl there (which should not be if you dried it thoroughly).
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[*] posted on 14-2-2010 at 16:48


Didn't use litmus to tell much acid was left, when some of the solution that it was recrystalizing from dripped onto a concrete floor it fizzed... I doubt NH4Cl is acidic enough to produce this effect. I just figured a quick wash in Acetone would handle it but I have no acetone or atlest not enough to be of anyuse. So perhaps I'll just recrystalize it once more which should remove more then enough to be of no problem to me. I only need it for Ammonia generation but didn't want to waste more NaOH then needed neutralizing residual HCl.




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[*] posted on 15-2-2010 at 01:20


Whether it be fizzling in the reaction with your concrete floor if it was pure saturated NH4Cl solution depends on what material it is on your floor. If the concrete is exposing calcite sand, then it may fizz somewhat. But that is not really scientific way of testing it, isn't it?

Is there a particular reason on why you can not properly dry it? Surely you can improvise a desiccator to dry it over anhydrous Na2CO3 or something? And yes, you could wash it with ethanol. It is nearly insoluble there.
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[*] posted on 15-2-2010 at 08:48


Somewhat surprisingly the Merck Index (9th & 10th editions) says NH4Cl is soluble in MeOH and EtOH.

This seemed so odd that I tried a quick test tube experiment. There was no appreciable dissolving, even when warmed, in 95% EtOH (Everclear).
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[*] posted on 15-2-2010 at 09:44



As per the wiki page of Ammonium Chloride, its Solubility in (ethyl)alcohol is 0.6 g/100 mL (19 °C).

gsd
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[*] posted on 15-2-2010 at 10:19


I managed to get a teflon thermometer adapter stuck in the ground glass joint of a flask by leaving it in there without lubricant for a long long time. I tried pulling it out with pliers to no avail. I'm hesitant to use a lot of force because I dont want to mess up threading. How can I get this to come out easily?
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[*] posted on 15-2-2010 at 11:10


UTFSE
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[*] posted on 16-2-2010 at 10:58


Entropy posted a link to the thread under his UTFSE. I read through the thread and pulled out what would seem to apply to your situation. I often use gentle heat via hot water from the tap. Sometimes an overnight soak in the wash basin does the trick if the hot water doesn't. Since a thermometer is involved flames are not recommended. Careful use of a narrow heat gun judiciously applied might work but is risky. Forget MID's with a thermometer. Forget about beer or soft drinks (too much sugar and other crap) but carbonated water could get the result. From here on out, NEVER NEVER leave ground glass joints any longer than needed for the application and don't use them without lubrication or sleeves. Teflon grease is spendy but a tube will last a long time. Teflon sleeves are good for non-vacuum uses. The tradition that st joints can be used without grease or sleeves at atmospheric pressure has not been born out by my experience. It might have been true when all st joints were precision ground but this is sadly no longer the case.



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[*] posted on 16-2-2010 at 12:39


Chemrox: I disagree here. All the glass I've used at uni has always been without lubrication. The only time I've had problems with stuck joints was back at school, and I happened to use grease that time! I think the trick lies in NOT twisting the joint; push to fit and leave it be.
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[*] posted on 16-2-2010 at 13:32


Quote:
The tradition that st joints can be used without grease or sleeves at atmospheric pressure has not been born out by my experience.
I tend to agree with DJF. I only grease when using vacuum or strong bases and I've never had a joint to stick so tight that gentle warming wouldn't open it. I think the real trick is to take the joints apart when you're done. That said, I do grease glass stoppered bottles used for storage because they don't seal too well without grease.
Quote:
It might have been true when all st joints were precision ground but this is sadly no longer the case.
I can't argue with that because almost all my glass is at least 25 years old.

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[*] posted on 20-2-2010 at 08:26
Cu2O to CuO


An easy one i think,

How to oxidize Cu2O to CuO in an aqueous mixture?

i tried KClO3, KNO3 and H2O2 and got very bad result, the mixture is still very brownish red. i was thinking about hypochlorite next, but I'm bored washing my Cu2O after each try. Any easy way with home chemical?

---
I generally use thermal expansion to solve any stuck glass joint, put the joint in the freezer and when it is cold try to separate it, if it still doesn't work get it out of the freezer and the outer glass will expand before the inner glass and they always (until now) separate.


[Edited on 20-2-2010 by Hamilton]
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[*] posted on 20-2-2010 at 08:42


I'm not sure its going to oxidise efficiently as its insoluble in aqueous solution, just like CuO. Personally I would try heating it strongly in air ("roasting" it); this should be sufficient.
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[*] posted on 20-2-2010 at 09:17


Quote: Originally posted by chemrox  

It might have been true when all st joints were precision ground but this is sadly no longer the case.


I use a thin coat of grease on my tapered joints and twist them into place. Then I separate them for cleanup right after use. I've never used a Teflon sleeve. I've never had a frozen joint.

I use a heavier coat of grease for vacuum distillations. Even with that I don't always get a good seal because I believe the joint is not precision ground. The faulty joint always has a cheap knock-off adapter or flask. When I replace these with a good brand like Kontes the joint seals.




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[*] posted on 20-2-2010 at 18:16


>How to oxidize Cu2O to CuO in an aqueous mixture?

These aren't soluble in water. However in strong base they can dissolve, so I'd look for an oxidizer that is either basic or compatible with same. Sodium hypochlorite with added sodium hydroxide would probably work (then you'd have to neutralize to precipitate the CuO).
But roasting in air seems like a much easier plan.
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[*] posted on 3-3-2010 at 23:18


Is there a method of preparing an alkyl halide from an alkyl amine besides using NOCl/NOBr or the Sandmeyer rxn? Thanks for any answer!

[Edited on 4-3-2010 by Bolt]
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[*] posted on 14-3-2010 at 12:04


here's another one,

can small particles of PVA like common white glue be chlorinated with HCl or (something similarly available) to produce PVC and acetic acid?
Juts like copper acetate turn to copper chloride and acetic acid when mixed with HCl.

For the CuO reply, in presence of NaOH, sodium hypochlorite do oxidize but not completly as it is decompose in O2 bubbles. The result was particules of Cu2O coated with CuO. As i found after dissolving in common vinegar. The roasting process work great.

Thanks

[Edited on 14-3-2010 by Hamilton]
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[*] posted on 14-3-2010 at 16:34


Quote: Originally posted by Hamilton  
here's another one,

can small particles of PVA like common white glue be chlorinated with HCl or (something similarly available) to produce PVC and acetic acid?
Juts like copper acetate turn to copper chloride and acetic acid when mixed with HCl.


[Edited on 14-3-2010 by Hamilton]


Definitely NOT, with HCl you will hydrolyse the Polyvinylacetate (PVAc) thus obtaining Polyvinylalcohol (PVA).

[Edited on 15-3-2010 by jokull]
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[*] posted on 16-3-2010 at 08:33


thx,

I tried to mix hcl and PVAc (white glue), i got a liquid more translucid than dilute PVAc. (same volume of PVA in HCl and in H2O) It's look partially soluble like PVOH should.(PVA, not to make me confuse will be write PVOH). Maybe there is some white pigments in white glue.

so i tried to write and equation. but can't figure it out very well.

(C<sub>4</sub>H<sub>6</sub>O<sub>2</sub>;)n + (HCl)m = (C<sub>2</sub>H<sub>4</sub>O)x + something else.

by smplicity (and because I don't know enough about possible resulting organic substance) i proceed with m=n

[C<sub>2</sub>H<sub>3</sub>(CH<sub>3</sub>COO)] +HCl = [C<sub>2</sub>H<sub>3</sub>(OH)] +[Cl + C<sub>2</sub>H<sub>2</sub>O]

The resulting substance doesn't smell Cl nor HCl nor CH3COOH. and C<sub>2</sub>H<sub>2</sub>OCl doesn't exist (well i think)

can you help me on the equation?

[Edited on 16-3-2010 by Hamilton]

i just return to my experiment and the solution of PVAc and HCl have become totaly translucid and very slightly yellow. On addition of water the PVAc (or whatever it is now) precipitate again. It look like it is soluble in very acid solution but not on dilute HCl.

[Edited on 16-3-2010 by Hamilton]
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[*] posted on 16-3-2010 at 09:17


Bolt, use a pyryllium salt and some sodium/potassium halide. The pyrylium converts the amine into a good leaving group (pyridine) and a simple Sn2 ensues with the halide ion.
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[*] posted on 18-3-2010 at 09:49


Quote: Originally posted by Hamilton  

so i tried to write and equation. but can't figure it out very well.

(C<sub>4</sub>H<sub>6</sub>O<sub>2</sub>;)n + (HCl)m = (C<sub>2</sub>H<sub>4</sub>O)x + something else.

by smplicity (and because I don't know enough about possible resulting organic substance) i proceed with m=n

[C<sub>2</sub>H<sub>3</sub>(CH<sub>3</sub>COO)] +HCl = [C<sub>2</sub>H<sub>3</sub>(OH)] +[Cl + C<sub>2</sub>H<sub>2</sub>O]

The resulting substance doesn't smell Cl nor HCl nor CH3COOH. and C<sub>2</sub>H<sub>2</sub>OCl doesn't exist (well i think)

can you help me on the equation?

You mean the hydrolysis equation? You wrote no water in the equations above, so it is not clear what you want. Perhaps you should first read something about ester hydrolysis, because from what you wrote above it looks like you should. Try putting "ester hydrolysis" keywords in a search engine or just open a basic level organic chemistry book (most will have a chapter on various hydrolyses). Besides "Cl" is chlorine radical and as such can not be the end product of any reaction (it combines either with itself giving Cl2 or with something else). Products are end results of reaction pathways and not of acrobatic writing with chemical symbols. Each bond that is broken must be accounted for by the formation of new ones.

Anyway, the hydrolysis equation would be:

[-CH<sub>2</sub>-CH(OCOCH<sub>3</sub>;)-]<sub>n</sub> + nH<sub>2</sub>O <=> [-CH<sub>2</sub>-CH(OH)-]<sub>n</sub> + CH<sub>3</sub>COOH

HCl is not a reagent in the reaction. It is there just to catalyse hydrolysis. Of course, with acid catalysed hydrolysis you can not fully hydrolyse polyvinyl acetate (unless you somehow remove acetic acid during the reaction). You should check a few examples of how polyvinyl acetate is hydrolysed. The patent literature is relatively abundant with such examples for it is a reaction used industrially. So try spending some time at Espacenet using the search engine.




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[*] posted on 25-3-2010 at 21:44


I am looking into the stability of Cu(I) oxide. According to wiki, it can be oxidized by "moist air". Do you suppose simply drying a copper(i) oxide precipitate in air would cause significant oxidation?
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[*] posted on 26-3-2010 at 07:23


Based on my experiences with CuCl, Cu(OH) and Cu2CO3 (or whatever passes for it) I'd say yes. All of these oxidize fairly quickly to Cu(II) when wet and exposed to air. Of course it still depends on what you would consider 'significant', the particle size, drying temp and so on; nonetheless I think that you would need to do something more than just pop it in the oven to dry if you want it to remain as Cu(I). Acetone and vacuum drying might help.
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