** Reply to note from Sandy King <sanking@hubcap.clemson.edu>
Sun, 19 Dec 1999 23:28:34 -0500
> Could anyone tell me what would be the most concentrated solution
> possible from sodium and potassium carbonate, and how these
> solutions should be mixed and stored?
I'll give it a shot, Sandy.
1. According to my old copy of the Chemical Rubber Handbook, the
solubility of Na2CO3, sodium carbonate, is 21.5 gram/100mL water at
20 deg. C. and 38.8g/100mL at 30 deg. C.
2. To prepare a saturated solution (which is what it is when it contains
the maximum possible amount, excluding unstable supersaturated
solutions) at room temp, ca. 20 deg. C, I would dissolve about 25 or
30 grams of the anhydrous compound (or the equivalent) in 100mL of
water (less any water of hydration, if you wish to be very certain) and
let it cool. Some solid should crystallize out. Or you could simply warm
the water to about 25-30 degrees C, dissolve the sodium carbonate
with stirring until no more seems to dissolve, and some solid is left
undissolved, and let cool. You should get the same result either way.
3. The solubility of K2CO3, potassium carbonate, is given as
112g/100mL H2O, increasing somewhat slowly with temperature.
4. To prepare a saturated solution of K2CO3, I would try to dissolve
about 120g per 100mL of water at about 25-30 deg C., or more
practically, just dissolve it with stirring until no more will dissolve, and
let cool.
The stirring can be done any way you're comfortable with. A
Teflon-covered stirring bar on a magnetic stirrer is the usual lab way,
but a clean glass or polyethylene or polypropylene manual stirring rod
will work just as well, with labor substituting for elegance and cost.
Both solutions are somewhat alkaline, and will slowly etch glass. I
would store in polyolefin plastic (polyethylene or polypropylene), but in
any case avoid glass stoppers, which probably no one outside a lab
would have anyway. If you're concerned about long term storage,
check on the long term compatibility of the solution with the plastic. To
the best of my recollection, neither PE nor PP should have a problem
with these solutions.
Either will absorb carbon dioxide from the air, and gradually increase in
content of the respective bicarbonate (e.g. sodium hydrogen
carbonate, aka sodium bicarbonate).
stan
-- Stan Johnson sjohnson@gwi.net 12/19/99 11:04pm
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