kriea22 - 22-6-2013 at 18:00
I'm having a problem. I set up a distillation apparatus and it doesn't seem to be working very well. I started with a 14/20 setup (which I'm beginning
to realize was not the correct taper for the scale I'm using). So I made a few adjustments and this is what I have now:
250 mL Roundbottom (14/20)
Stillhead with glass stopper (14/20)
Adapter (14/20-19/22)
Condenser (19-22) (Ice Cooler)
Receiving Flask
So I've been using 1:1 molar ratios of Sulfuric Acid and Potassium Nitrate, but I've only managed a few drops (after 2 hours). During the reaction I
can occasionally see vapor escaping through the other end, which should not be happening.
Here are my thoughts: I'm feeling that maybe this is due to the 14/20 taper. Maybe I should upgrade the reaction flask and stillhead to 19/22. Or
maybe even 24? Is there some kind of attachment I could use at the end of the condenser that will help salvage all that lost vapor? And maybe use an
Ice Bath for the receiving flask? I'm not sure if any of these things would make a sizable difference.
I would appreciate any advice. I need this damn thing to work. What kind of aspiring ChE would I be if I can't even set up a working Distillation
apparatus? lol
cyanureeves - 22-6-2013 at 19:06
i didnt know how either and thought everything should be air tight then i was told here that it shouldnt.now i just let it drip into the receiving
flask because unless i'm doing a vacuum distillation it might explode.the pressure will push your joints apart even if you are using keck clips
anyways but amazingly it stops fuming and just start to condensate.you will see the red fumes being pushed out making way for clear nitric distilling.
you did not mention acid concentration and nitrate purity,believe it or not but nitric acid forms in the condensor and drips out even if fumes escape
i do it all the time.
[Edited on 6-23-2013 by cyanureeves]
[Edited on 6-23-2013 by cyanureeves]
kriea22 - 23-6-2013 at 11:21
Hm, well I'd imagine if vapor is escaping then you are losing yield. My point is that I distilled for 2 hours unsuccessfully and I'm not sure why. Is
the 14/20 taper to blame? As I said before I have a 19mm tapered condenser, so if i bought new 19/22 glassware, would it be sufficient for a 250 mL
reaction flask? Or do I need to buy a new condenser with a 24 i.d. taper? Assuming that this would make a difference which no one has confirmed yet.
If anyone can confirm this, then I can proceed and I'll buy a vacuum adapter at the end and just not use the vacuum (leaving a small opening for air
to flow).
plante1999 - 23-6-2013 at 11:28
If you want to get rid of your 14/20 I would take it. I don't think the problem is the glassware honestly, are you sure your reagents are pure enough,
and if yes you may want to heat way stronger your flask.
Pulverulescent - 23-6-2013 at 12:01
| Quote: |
| I'm having a problem. |
You didn't mention temperatures?
If your thermometer was correctly placed (bulb adjacent to the vapour outlet), it should go to 120°C by the end of the distillation . . .
Bot0nist - 23-6-2013 at 13:18
I agree with hiss, I bet you didn't run hot enough, and use a bit more conc sulfuric if you need to. It makes for a much more liquid reaction,
especially toward the end, when it becomes thick and mag stirring becomes difficult.
Run the condensor as cold as you can, and make sure there is a way for non-condensed vapor to exit the system, preferable into a hydroxite solution.
If your condensor is cold enough and long enough you will not loose very much acid at all. you cant seal the system though. the gasses have to flow
from the hot reation vessle, through a cold condensor, and then out at the end.
Oscilllator - 23-6-2013 at 23:15
well first off your stoichiometry is off, you need 2:1 KNO3:H2SO4.
Also, I second what other people have said about the temperature. If it isn't going fast enough, then crank up the heat until something happens!
woelen - 24-6-2013 at 00:17
Using 2 moles of KNO3 for 1 mole of H2SO4 is not good for this reaction. You need excess H2SO4, otherwise you get a hard solid cake in your heated
flask!
An already better approximation of the reaction is
KNO3 + H2SO4 --> HNO3 + KHSO4, suggesting a 1 : 1 molar ratio.
In practice I would add even a little more H2SO4 and use a 1 : 1.5 molar ratio. You don want to end up with a lot of solid matter in your flask, which
may result in heavy bumping and/or cracking of the flask. You need to keep the material in your heated flask liquid at all time during the
distillation process!!
kriea22 - 26-6-2013 at 16:56
Thank you guys for the feedback. Seriously, I greatly appreciate it. I'm going to run the reaction again this weekend and see how it goes.