Random - 16-8-2010 at 08:02
I made some magnesium citrate from magnesium metal and citric acid. It looks that it's very soluble as I see nothing insoluble in solution. I want to
make magnesium carbonate from that, can I do that with addition of sodium bicarbonate to the solution? Will magnesium carbonate precipitate from the
solution?
chemrox - 16-8-2010 at 10:21
I would guess that putting dry ice into the mix would precip MgCO3. It's solubility in water is fairly low: 6.21X10(-3). You would then have citric
acid solution and the ppt carbonate. Citric acid solubility is 1.3X10(3) g/l.
Just for fun look up the carbonate in water equilibria. It's an interesting, pH dependant set. The presence of citric acid might not influence the
outcome greatly and dry ice would provide plenty of excess if needed.
[Edited on 16-8-2010 by chemrox]
unionised - 16-8-2010 at 10:56
"I would guess that putting dry ice into the mix would precip MgCO3. "
I wouldn't.
Citric acid is a fair bit stronger than carbonic. Lemon juice will dissolve magnesium carbonate. It might work under some dangerously high pressure,
but that's not very helpful.
Adding bicarbonate of soda to a solution of magnesium citrate will produce a precipitate of the carbonate. It will work better if you heat the mixture
to drive off excess CO2.
Alternatively, you could add boiling water to some sodium bicarbonate. The bicarbonate will decompose and the sodium carbonate formed will dissolve in
the water. You can then use this solution to precipitate magnesium carbonate from the citrate solution.
Random - 16-8-2010 at 13:48
I am interested in adding boiling water to NaHCO3 to decompose it to Na2CO3, but will all NaHCO3 decompose with mixing boiling water with it or I need
to boil bicarbonate solution longer time?
bbartlog - 16-8-2010 at 18:31
You need to boil sodium bicarbonate for a little while (I usually go ~20 minutes) to convert it all to Na2CO3. Even then I wouldn't use it for
analytical purposes, i.e. I think this is good enough to get to 99% but maybe not 99.99% conversion.
unionised - 17-8-2010 at 10:47
Most of the reaction occurs during the first few seconds- try it. Put a teaspoon of bicarbonate in a cup and fill the cup with boiling water as if you
were making a cup if instant coffee.
In this case, even 50% conversion to carbonate would do fine.
If I was doing it for analytical purposes (and I have done in the past) I would do it properly. Heat the powder in an oven to constant mass at about
200C.
turd - 18-8-2010 at 23:17
Magnesium citrate to carbonate, seriously?
Burn the sucker. 
http://dx.doi.org/10.1016/0040-6031(94)85117-4
Random - 19-8-2010 at 00:08
I mixed magnesium citrate and na2co3 that was made by mixing NaHCO3 with boiling water. No precipitate was seen...
bbartlog - 19-8-2010 at 07:03
What volumes are you working with? Magnesium carbonate is very slightly soluble in water. Also, how was your reaction between magnesium metal and
citric acid conducted?
BTW if your goal is magnesium carbonate and not just investigation of the compounds you have at hand, I would suggest magnesium sulfate (epsom salt)
and sodium carbonate as a cheap and easy route.