Conversation started Mar 31, 2016 at 18:13.
IͶΔ
IͶΔ
Mar 31, 2016 18:13
Why does quickly cooling a saturated solution cause precipitation?
pH13
pH13
does it?
IͶΔ
IͶΔ
It usually does.
pH13
pH13
stuff is better dissolved in hot solvents, why when cooling it, it's again not so good dissolved which follows in precipitation
!!wiki/Recrystallization_(chemistry)
Chemobot
Chemobot
Recrystallization (chemistry)
In chemistry, recrystallization is a technique used to purify chemicals. By dissolving both impurities and a compound in an appropriate solvent, either the desired compound or impurities can be coaxed out of solution, leaving the other behind. It is named for the crystals often formed when the compound precipitates out. Alternatively, recrystallization can refer to the natural growth of larger ice crystals at the expense of smaller ones. == ChemistryEdit == In chemistry, recrystallization is a procedure for purifying compounds. The most typical situation is that a desired "compound A" is ...
IͶΔ
IͶΔ
Yes, but why does slowly cooling it sometimes make a supersaturated solution?
I mean, why the different results in the method of cooling?
What happens in quickly cooling that doesn't in slowly cooling?
Hippalectryon
Hippalectryon
Mar 31, 2016 18:20
Reorganisations. Isnt it just like how if you hit supercooled water it freezes, but if you lightly move it it stays liquid ?
IͶΔ
IͶΔ
@Hippalectryon This does not provide an answer to the question. To request clarification from the author, leave a comment below their post.
I didn't mean supercooling.
Oh wait.
Hmm . . .
pH13
pH13
for me, your second question also sounded like supercooling
Ramanewbie
Ramanewbie
@hippa The bot on my RPi apparently can't display images. !!img/[] return error. Why ?
Chemobot
Chemobot
<An error occured : cannot identify image file. Check your molecule's name.>
Ramanewbie
Ramanewbie
That error ^
Hippalectryon
Hippalectryon
Mar 31, 2016 18:22
I gtg :( sya
Ramanewbie
Ramanewbie
k
Brian
Brian
@IͶΔ Physical agitation/disruption. In order for crystals to form (or for gas bubbles to form, too, for that matter), there's sort of an "activation cluster size" that it has to get across.
IͶΔ
IͶΔ
Oh
Brian
Brian
Lone dissolved ions/molecules are more stable than clusters of, say, four crystal units (no idea if that's the right number).
IͶΔ
IͶΔ
To Googlez
Brian
Brian
Mar 31, 2016 18:24
But, once you get beyond some critical number of particles, it'll happen rapidly.
Alternatively, surfaces & edges & such can act as a 'catalyst' for nucleation
pH13
pH13
@Brian when reading this, I have to think about a fancy paper about very very very clean water that freezes way below 0 °C
Brian
Brian
Either way, you have to 'leapfrog' up to a large enough cluster size such that continuing to form a larger crystal/bubble is energetically favorable.
(I guess "Free-energetically favorable," to be precise)
IͶΔ
IͶΔ
:o It all makes sense now
Brian
Brian
In theory, actually, both fast cooling and slow cooling should have the same potential for overcooling
But there's essentially always some physical disturbance associated with fast cooling that provides the 'bump' needed to get over the nucleation activation barrier
It's why in chem lab when you're boiling water for a hot water bath you're always supposed to scratch the beaker you're boiling in, or to add boiling chips.
Both provide nucleation sites that catalyze water vapor bubble formation.
</science rant>
 
Conversation ended Mar 31, 2016 at 18:28.