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xfusion44
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[*] posted on 28-11-2014 at 05:53


@greenlight

I've bought 25% ammonia solution and ethyl acetate - I will still try to get EtOAc from NPR, but just in case ;)




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[*] posted on 28-11-2014 at 19:09


There's a white crystalline powder in an unmarked container in my lab; I think it might be anhydrous sodium acetate if memory serves; there's nothing dangerous that it could be, though.

How can I test to see if it's sodium acetate or not? I tried adding acid and trying to detect the smell of acetic acid, but the odor was too ambiguous. I can already tell that it's hygroscopic, as it clumps up as soon as a bit of water is added.




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[*] posted on 28-11-2014 at 19:48


You can add a non-volatile acid and heat it up- the vinegar smell should be more obvious. A flame test should tell you if it's sodium acetate. A solution of sodium acetate added to a solution of copper(II) sulphate will give a slightly more intense blue without giving a precipitate.



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[*] posted on 29-11-2014 at 08:55


I have a problem: how do I know the density of dissolved gas in water (ammonia)? I calculated, that there is 342,466 liters of gas in one kilogram of 25 percent w/w ammonia and I would like to know the volume of one kilogram of 25 percent w/w ammonia solution, but I can't just take usual density of ammonia into account, since the volume of one kilo 25percent ammonia would be above 343 liters. Please help :-/

Thanks! :)

PS: I know from wiki, that the volume of 1kg of 25 ammonia is about 1,01l, but there must be a way to calculate that, right? For example: how do you know, that 342.5l of ammonia gas is just about 260ml when dissolved in water? Or is it actually ammonium hydroxide, and there is no actual gas dissolved?

[Edited on 29-11-2014 by xfusion44]




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[*] posted on 30-11-2014 at 17:19


Are you making your own Ammonia solution by bubbling Ammonia gas into water or did you buy store brought.
If it is dilute Ammonia it will be 10-15% by weight and contain 48-95g/L or if concentrated it will be 25%. The 25% solution has a density of 0.907 g/cm3 and should have 226g/L Ammonia.
"Ammonia solutions decrease in density as the concentration of dissolved ammonia increases, the density of a saturated solution is 0.88 g/ml and contains 35% ammonia by mass, 308 g/lw/v, (308 grams of ammonia per litre of solution)."

Ammonium hydroxide is Ammonia gas dissolved in water, it is the same thing as Ammonia solution just a different name.

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[*] posted on 30-11-2014 at 18:45


Some people will refer to aqueous ammonia as "ammonium hydroxide", but that's incorrect, as the majority of the ammonia is unionized.



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[*] posted on 30-11-2014 at 18:53


True. But in applications where ammonia solution is being used for its alkaline properties it makes sense to emphasise the "hydroxide" especially since the equilibrium dictates that it will be replaced as it is being used.
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[*] posted on 30-11-2014 at 20:12


Quote: Originally posted by j_sum1  
True. But in applications where ammonia solution is being used for its alkaline properties it makes sense to emphasise the "hydroxide" especially since the equilibrium dictates that it will be replaced as it is being used.


Not really, because the acid you're reacting it with will react faster with the ammonia than the minimal hydroxide ion in solution, because the concentration's a lot higher.




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[*] posted on 30-11-2014 at 20:25


Again correct.
But nomenclature is communicating. If your purpose is to communicate that OH- ions are available in the solution (I am thinking of beginning chemistry students) then calling it by both names emphasises the point. It also opens up the discussion of exactly how much of the ammonia hydrolyses in solution, which is precisely the conversation you want to have.

I guess my point is that in the context of my work I have never had a problem with "ammonium hydroxide" nomenclature and can see some benefit to it.
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[*] posted on 1-12-2014 at 01:14


@greenlight

No, I was making acetamide with it, I bought 25 ammonia or NH4OH, whatever is correct to say... I wanted to calculate how much of each I mix...

However, I failed! First, I tried with my own EtOAc and 25 ammonia and 3h mixing, until all has reacted... After evaporation, there was nothig left. Again, with pure EtOAc and 5h mixing, after evaporation, there was nothing left :( I was expecting some crystals of acetamide :-/ Reaction mixture turned cloudy when it was on warm place, so I thought that some crystals are forming, but nothing...

Don't know, what else to do :(

Polesch on this forum didn't have problems, even with 9 percent ammonia, but I have with 25.

Also, I noticed, that during mixing, half of liquid was gone, but I don't know, how...

Thanks

[Edited on 1-12-2014 by xfusion44]




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[*] posted on 1-12-2014 at 03:28


Sorry to hear it's not working out for you Xfusion.
Did the solution form two separate layers like Polesch's when you mixed the Ethyl acetate with the Ammonia solution and then turn into one.
Maybe the reaction takes much longer to take place, you could try again and leave it on stir for 24 hours on a magnetic stirrer like Polesch did before evaporating. Polesch also left it to sit in the evap dish for three days before evaporating with heat if you have the time.

I also found this Acetamide synthesis for you from Ammonmia and Ethyl acetate with pictures.

http://lulelaboratory.blogspot.com.au/2013/08/preparation-of...

I think the 24 hour wait is needed for the Acetamide to form because both Polesch's and the linked synth have the waiting period.


[Edited on 1-12-2014 by greenlight]
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[*] posted on 2-12-2014 at 18:57


Yes, it did form two layers, which were then turned into one, after stirring for 5 hours.

Maybe it does take longer, but I'm afraid, that all of the solution will evaporate during stirring, because I've lost more than a half of it last time, during stirring and I still don't know why? I was stirring it on a cold place outside...

I'll check the link, when I'll have some time.

Thanks :)




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[*] posted on 3-12-2014 at 06:00


Put some cling-film over the top, or something; and reduce your stirring rate. Try doing the reaction in a conical flask rather than a beaker; that should help to prevent losses due to evaporation.
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[*] posted on 4-12-2014 at 06:53


Does oxygen have a smell?
When I let H2O2 decompose at an increased rate, it smells awful... I wonder what it is I smell.
It both smelt the same with potassium permanganate as a catalyst, and powdered lead as a catalyst.




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[*] posted on 4-12-2014 at 07:28


I know exactly what you mean. The smell actually is quite acrid.
What you smell is H2O2, not oxygen. The H2O2 comes into the air in the form of very small droplets, which are formed, due to the bubbling of the liquid. These tiny droplets evaporate and give vapor of H2O2.

This also demonstrates how easily material from an aqueous solution can become airborne. For this reason, I always am very careful with bubbling solutions which contain highly toxic material dissolved. E.g. I would never add a carbonate or magnesium to an acidic solution, containing mercury salts. The bubbles of CO2 or H2 then take with them tiny droplets of mercury-containing liquid which becomes airborne. A good safety measure in such experiments is to cover the test tube with a piece of paper tissue, or loosely push some wadding in the open end of the test tube. The produced gas easily moves along the paper tissue or wadding, but the droplets remain behind.




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[*] posted on 4-12-2014 at 07:30


Evidently the liberated oxygen volatilizes some hydrogen peroxide. So what you are smelling is the "slightly sharp" (according to wikipedia) smell of hydrogen peroxide. I've never worked with the stuff, so I cannot attest to its odour.
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[*] posted on 4-12-2014 at 08:27


I agree with the 'slightly sharp' or 'acrid' description.
Thanks for the answers. So to protect my nose, I will perform this in a fumehood next time.




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[*] posted on 9-12-2014 at 19:59


I am trying to electrochemically convert copper sulfate solution to a dilute solution of sulfuric acid, using a computer psu, but it keeps shorting out.
Besides diluting the salt solution, how else can i prevent constant shutdown of the psu?

Would placing a load resistor in series before the setup work?
How would it affect the current/voltage of the setup?
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[*] posted on 9-12-2014 at 22:27


I'm no expert, but I can tell you that placing the electrodes further apart will increase the resistance - no need to add resistors. I should think that increasing the resistance would decrease the current, since current = volts/resistance.
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[*] posted on 10-12-2014 at 01:45


I had the same problem until I blew something in the psu. I haven't yet pulled it apart to find what went wrong. Probably not fatal but it did highlight the benefit of a resistior in series.
I have switched to a current regulated power supply. Much better. If you can afford it, that's the way to go. The biggest difficulty now is chewing through anodes. Pt is probably desirable but expensive. My next choice is to get some graphite scourging electrodes from a welding shop, peel off the copper (or just let it go into the solution) and be prepared to filter the carbon out of the product.
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[*] posted on 10-12-2014 at 04:52


I got a platinum coated titanium electrode from ebay(http://goo.gl/e9NycX), but i'm still using a regular PSU for the power supply.

So increasing the resistance would decrease the current, so it would take longer to convert it?
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[*] posted on 10-12-2014 at 07:53


I've bought fertilizer grade calcium nitrate, but I'm not sure if it is anhydrous or tetrahydrate. Is there a possibility to determine if it is anhydrous or not? Sorry if this is a silly question...
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[*] posted on 10-12-2014 at 08:10


well you can convert calcium nitrate tetrahydrate to anhydrous by heating it to 132 °C where it decomposes.

Alternatively, you can figure it out by finding the density of the solid
2.504 g/cm3 (anhydrous)
1.896 g/cm3 (tetrahydrate)
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[*] posted on 10-12-2014 at 09:15


Thanks dude!
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[*] posted on 10-12-2014 at 09:22


Finely powder it if possible; if it absorbs water and gets clumped together, it's probably anhydrous. If it loses a significant amount of weight with heating as previously suggested, it was a hydrate.



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