Acuarey
Harmless
Posts: 3
Registered: 7-10-2015
Member Is Offline
Mood: No Mood
|
|
Does it happen? Is it dangerous in anyway?
Hello! First I´d like to apologize to any english mistakes(Not my native language XD) and apologize to any major "chemichal mistake"(Still in first
year-High School)
I have a lot of fun just watching Chemical Reactions happening!
And I have some doubts on how some of them work (Or might not work)
MgCl2 + 2NaHCO3 -> MgCO3 + 2NaCl + H2O + CO2
This first reaction seems "doeble", since I´d get as a result na insoluble salt and a weak acid (H2CO3), which will probably decompose.
This second "part" is the one which worries me...
MgCO3 + H2O -> MgO + H2O + CO2
Is this the way it works? Is the Mg going to change places with the Hydrogen, producing the H2CO2, which will decompose?
Yes? No? What did I get wrong?
MgO + H2O -> Mg(OH)2
This reaction is simple, and I am pretty sure it should happen
Mg(OH)2 + 2NaHCO3 -> 2H2O + Na2CO3 + MgCO3
This one is a bit tricky, because it involves "adding" the Sodium Bicarbonate, but I think I got it right. Any thoughts?
MgCO3 + H2O -> MgO + H2O + CO2
MgO + H2O -> Mg(OH)2
And then we have the Magnesium Hydroxide "Regenerated" again. Therefore the "Cycle" should go on, as long as there is enough NaHCO3, since all the
other compounds are a result of a previus reaction.
And the general equasion would be:
MgCl2 + 4NaHCO3 -> 2NaCl + Na2CO3 + H2O + 3CO2 + Mg(OH)2
And if there was more Sodium Bicarbonate:
MgCl2 + 6NaHCO3 -> 2NaCl + 2Na2CO3 + 2H2O + 4CO2 + Mg(OH)2
And so on...
But all that depends on The "Second" Reaction, because that is the reaction involved in the "regeneration" of the the Mg(OH)2 and also the one which I
think doesn´t happen.
I fail to belive that Hydrogen would change places with the Magnesium....
Thank you for your help, see you soon.
|
|
|
zed
International Hazard
Posts: 2278
Registered: 6-9-2008
Location: Great State of Jefferson, City of Portland
Member Is Offline
Mood: Semi-repentant Sith Lord
|
|
Dangerous? Yup. MgCO3 It may produce a spine chilling, screeching effect, when applied to a blackboard. In this part of the world, we call it
chalk.
Pretty insoluble in water. And pretty stable.
Takes a lot of heat to convert it to MgO + CO2.
https://en.wikipedia.org/wiki/Magnesium_carbonate
More interesting is CaCO3. Which may be converted to its oxide in the same manner. However, CaO (quicklime) is commonly used in a bunch of neat
reactions. Like CaO+C+heat= Calcium Carbide. Calcium Carbide can then be reacted with H2O, to produce Acetylene. Or, Calcium Carbide, can be
reacted with H2 to produce CaH2, a very useful material.
https://en.wikipedia.org/wiki/Calcium_carbide
[Edited on 7-11-2015 by zed]
[Edited on 7-11-2015 by zed]
|
|
|
hissingnoise
International Hazard
Posts: 3940
Registered: 26-12-2002
Member Is Offline
Mood: Pulverulescent!
|
|
| Quote: | | Dangerous? Yup. MgCO3 It may produce a spine chilling, screeching effect, when applied to a blackboard. In this part of the world, we call it chalk.
|
Errr! Chalk is calcium carbonate!
|
|
|
ave369
Eastern European Lady of Mad Science
Posts: 596
Registered: 8-7-2015
Location: No Location
Member Is Offline
Mood: No Mood
|
|
Magnesium hydroxide? You'd better not try any large scale synthesis involving milk of magnesia! This goopy, slimy precipitate is a major pain in the
ass to filter! It readily clogs any filter, and a Buchner set does not help!
Smells like ammonia....
|
|
|
AJKOER
Radically Dubious
Posts: 3026
Registered: 7-5-2011
Member Is Offline
Mood: No Mood
|
|
MgCl2 + 2NaHCO3 -> MgCO3 + 2NaCl + H2O + CO2
I think a better understanding on what is occurring can be gained by looking at successive reactions:
First:
MgCl2 + 2NaHCO3 = Mg(HCO3)2 + 2NaCl
Now, Magnesium bicarbonate is unstable decomposing on heating over 5O C, or just on standing for a day so (especially, I suspect, subject to pressure
fluctuation). To understand why, we have the amphoteric bicarbonate ion (see, for example, discussion at http://www.ausetute.com.au/acidbase.html ):
HCO3- --> CO3(2-) + H+ (more so in alkaline, pH > 7 conditions)
HCO3- + H+ --> CO2 + H2O
That is, the equilibrium moves to the right under acidic conditions. I could also express this as (upon adding OH- to both sides):
HCO3- (aq) --> OH- + CO2 + H2O (low pH environment)
Note, for a small change in pH, we have in the case of magnesium, either the formation of the highly insoluble carbonate or the hydroxide! The
formation of such precipitates will further move the equilibrium to the right, hence the instability of Mg(HCO3)2.
The bicarbonates of calcium, ...., silver are similarly unstable.
-------------------------------------------------------------
I found a reference on my observation of instability on Mg(HCO3)2 on standing, to quote:
"He further found that the metastable solution decomposes just on standing and that the addition of a small quantity of magnesium
carbonate crystals will destroy the metastability, causing CO2 gas to escape and precipitating an undetermined solid phase"
Another important cited equation to understand the possible loss of CO2 on standing (with an associated rise in pH) and the formation of insoluble
magnesium oxide is the equilibrium reaction:
MgO + 2 CO2 + H2O = Mg(HCO3)2
[Edit] An interesting hypothesis that occurred to me if the authors comment that a small quantity of magnesium carbonate crystals could destroy the
metastability, a temporary fluctuation in, say, pressure to aqueous Mg(HCO3)2 on standing (or, a minor rise in temperature, or as a consequence of
simple evaporation) could result in the loss of some CO2, a rise in pH, and the formation of a small quantity of magnesium carbonate crystals, to act
as a seed for the decomposition of the solution, even though the triggering condition may no longer be present.
Source: "DEDOLOMITIZATION, AND ITS RELATION TO A POSSIBLE DERIVATION OF A MAGNESIUM-RICH HYDROTHERMAL SOLUTION", by George T. Faust, pages 808 and
809 at https://www.google.com/url?q=http://www.minsocam.org/ammin/A...
[Edited on 7-11-2015 by AJKOER]
|
|
|
zed
International Hazard
Posts: 2278
Registered: 6-9-2008
Location: Great State of Jefferson, City of Portland
Member Is Offline
Mood: Semi-repentant Sith Lord
|
|
Yup. I may have misfired. MgCO3 is sold as chalk alright. But, it is generally sold as Gym Chalk. The stuff gymnasts apply to their hands.
Do, be careful how much you eat. It can make you shit like a goose. No fooling.
Magnesium is poorly absorbed from the gastrointestinal tract, so it can produce, when ingested, an explosive laxative effect.
Usually ingested in the form of Magnesium Sulfate, Epsom Salt.
[Edited on 7-11-2015 by zed]
[Edited on 7-11-2015 by zed]
|
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
