SunriseSunset
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Saturate with Carbon Dioxide?
When a procedure calls for (After the mix has stood for a few hours at room temp, crushed ice is added and the solution is saturated with carbon
dioxide. this causes separation of product as an oil which solidifies on standing overnight in an ice bath), I'm wondering if that it means to bubble
CO2 gas into the solution until it's saturated. Wouldn't that produce Carbonic acid (a weak acid).
After the addition of crushed ice, the solution should still be pretty basic from excess NaOH(aq) remaining left over.
So I assume the purpose of adding a weak acid is to gently neutralize the pH, hence allowing post-separation. But could you over acidify it in this
case or does the word saturate literally mean add CO2(g) until it reaches maximum equilibrium.
I'm wondering if you avoided adding CO2(g) all together, how might it affect the workup overall? I'm sorry I have so many questions but if anyone
could answer some of them, it would be nice
CitedOrganic Syntheses, Coll. Vol. 2, p.622 (1943); Vol. 15, p.85 (1935)
Why do chemists call helium, curium and barium the medical elements?
because if you cant helium or curium, you barium! - Heimerdinger
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elementcollector1
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Well, carbon dioxide isn't all that soluble in water anyway, but if you did have a pH problem, you could honestly just heat it gently for the
CO2 to escape, as carbonic acid decomposes very easily.
Elements Collected:52/87
Latest Acquired: Cl
Next in Line: Nd
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diggafromdover
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Carbonic acid is a strong acid, being almost completely dissociated. It is also only found in low concentrations. If a concentrated product could be
produced by saturating an aqueous solution with Carbon Dioxide, then the Coke can would be history. Instead, you got fizzy solution.
Put a cap on your chilled product to allow more CO2 to dissolve and don't sweat the H2CO3
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SunriseSunset
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so if I were to keep the solution at 5*C and bubble CO2 through it for an infinite amount of time, any idea how low the pH could go at best or worst?
If it was just water alone. I need to practice my pKa/pH conversion skills actually lol it's been a while!
Ok thanks
Why do chemists call helium, curium and barium the medical elements?
because if you cant helium or curium, you barium! - Heimerdinger
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Mesa
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Quote: Originally posted by diggafromdover  | Carbonic acid is a strong acid, being almost completely dissociated. It is also only found in low concentrations. If a concentrated product could be
produced by saturating an aqueous solution with Carbon Dioxide, then the Coke can would be history. Instead, you got fizzy solution.
Put a cap on your chilled product to allow more CO2 to dissolve and don't sweat the H2CO3 |
I can't tell whether or not you are joking...
Either way, almost no part of the post is correct/accurate. CO2(or H2CO3 if you want to irritate your teacher) is a weak acid.
And coke isn't fizzy enough.
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SunriseSunset
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^ lol!
and apparently aqueous solutions of "carbonic acid" usually balance between CO2(aq) <-> H2CO3 I guess depending on temp + pressure (Wikipedia)
But it still doesn't tell me where the point of molar concentration in a given temp or pressure becomes a saturated solution and what the pH would be.
Regardless, it did give me the equations to find out for myself. But as long as it's a weaker acid and aids the process of separating product to
crystallize over night, I assume it's important to do for a number of reasons. Mostly probably to treat the excess NaOH I imagine.
Why do chemists call helium, curium and barium the medical elements?
because if you cant helium or curium, you barium! - Heimerdinger
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blogfast25
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Ahem. Want to quit spreading misinformation maybe, already? 
For H<sub>2</sub>CO<sub>3</sub>, pK<sub>a1</sub> = 3.6 (1st deprotonation). Care to calculate the degree of
dissociation from there, bearing in mind most of it is present as CO<sub>2</sub>(aq), not as carbonic acid
(H<sub>2</sub>CO<sub>3</sub> ?
Unless there are very specific reasons for it, using CO<sub>2</sub> as a neutraliser (acid) is really overkill.
[Edited on 9-6-2015 by blogfast25]
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