James Ikanov
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Distilliation by freezing
So I was doing some reading... and although aggravating, would it be possible to distill something such as H2O2 or HNO3 out of reliably water by
freezing?
I have done a small batch (very tiny) of H2O2 and had some success reaching higher concentrations, but HNO3 seems like it might be more pesky.
I've tried making low concentrations using the Oswalt process, and I'm currently on version two of attempting to make a device that can reliably
decompose Ammonium Nitrate into nitric oxides.
However, I usually end up with really low yields, unusably low.
I read that the freezing temperature of nitric acid is around -40 degrees...
would it be possible to distil low concentrations of nitric acid out to much higher ones by freezing the water it's mixed with?
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Steam
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HNO3 is a strong acid, meaning it will fully dissociate in water to form H+ and NO3 -. Similar to the way salt will dissolve in water. When it does
this, the freezing point will be lowered. See "freezing point depression".
In short, no you can not, you would have to preform a standard distillation.
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BromicAcid
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Distillation involves actually converting a liquid to the gas phase then taking it back to a liquid. Freezing a liquid is quite different from a
distillation. What you are suggesting is essentially a fractional crystallization, trying to crystallize a specific component of a mixture and leave
the remainder liquid. Hydrogen peroxide as you have found out can be a good candidate for this method of purification, to a point. Issues that most
people have involve mechanical losses and cooling too quickly resulting in occlusion and the whole mass turning into a useless chunk. Since most
people are starting from 3% hydrogen peroxide it doesn't take much of a loss to cause a failed attempt. There are quite a few threads around here on
the subject of concentrating hydrogen peroxide, some of those that touch more on freezing are:
http://www.sciencemadness.org/talk/viewthread.php?tid=1325
http://www.sciencemadness.org/talk/viewthread.php?tid=11382
http://www.sciencemadness.org/talk/viewthread.php?tid=30193
Just so you are aware the search engine around here is of limited utility, you are better off going to Google and searching for what you want with
site:sciencemadness.org tacked onto the end of your search string.
I do disagree with Steam. I think that <u>in theory</u> nitric acid should be possible to freeze out, but the freezing point curve is a
bumpy ride:
http://nitrogen.atomistry.com/physical_properties_nitric_aci...
From the chart theoretically you could might be able to get the HNO<sub>3</sub>*3H<sub>2</sub>O material to come out of your
solution as the most concentrated since at temperatures below that that material would start to freeze out first. However, as with the
H<sub>2</sub>O<sub>2</sub> issues caused by the high dillution, you may end up with the same problems, i.e., mechanical losses
becoming significant. However, there are other ways to get nitric acid from ammonium nitrate without going through the trouble of decomposing to the
nitric oxides but that's a subject for a different thread.
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