soma
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degraded MgO
I've been having problems with MgO. It seems to react easily with CO2 in the air and becomes the carbonate. I've had some however, that doesn't seem
to degrade real easily.
I just received about 2 lbs. that seems to be pretty badly degraded -- it fizzes alot when adding it to (ascorbic) acid. I'm using it make Mg
Ascorbate.
In looking to buy MgO I saw that there are quite a few different types. I'm wondering if there's a type that is purer and degrades slower?
I don't want to use the carbonate because, as it loses CO2, it becomes too alkaline and it's hard to adjust it correctly. (I'm keeping it in solution)
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ave369
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Why don't you just calcine MgO? It guaranteedly turns any carbonate impurities back into the oxide.
Smells like ammonia....
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soma
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How would you do that? Just heat it up in a metal pan on a gas stove? I wouldn't know how to measure the temperature to keep it in the light burned
range.
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ave369
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Yeah, a metal pan and a gas stove will do. Don't worry about the temperature, you can't overdo it: MgO does not decompose.
Smells like ammonia....
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blogfast25
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You'll need minimum 350 C for a prolonged time to calcine MgCO3 to CO2-free MgO.
Absorption of CO2 by MgO probably depends on how long it was calcined for, as most metal oxides become more inert on longer
calcining.
That's why home made MgO is probably more prone to CO2 absorption than commercial grades.
[Edited on 16-3-2016 by blogfast25]
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woelen
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Why is it a problem if there is some carbonate in the MgO? If I were to make Mg-citrate from it, I would add a slight excess amount of the MgO/MgCO3
and allow it to stand for a day or so. MgO and MgCO3 are only very sparingly soluble and in the solution with a lot of Mg(2+) ions it will even be
less soluble. No need to have precise stoichiometric ratios for this reaction.
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blogfast25
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Yes, for preparing any Mg salt some MgCO3 contamination is irrelevant.
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soma
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The problem with using MgCO3 for ascorbate in solution is that the pH doesn't remain constant. The pH increases as the solution loses CO2 and can
become too alkaline.
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soma
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I've read that dead burned MgO is unreactive. Does that mean that it won't react with acids, or that it just reacts more slowly?
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blogfast25
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Quote: Originally posted by soma  | | The problem with using MgCO3 for ascorbate in solution is that the pH doesn't remain constant. The pH increases as the solution loses CO2 and can
become too alkaline. |
Not really. MgCO3 dissolves in acids with release of CO2. Because ascorbic acid is a weak acid, allow some time and heat mildly
if possible.
| Quote: Originally posted by soma | | I've read that dead burned MgO is unreactive. Does that mean that it won't react with acids, or that it just reacts more slowly?
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Many oxides do become very inert on hard and prolonged calcining. Whether this is also true for MgO I do not know.
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