Oggas
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Calculating solubilities
I want to make NaOH by reacting Na2CO3 with Ca(OH)2. So i need to know how much water i need in order to dissolve both the Na2CO3 and the Ca(OH)2 in
order to make an as concentrated NaOH solution as possible.
The solubility for Ca(OH)2 : 0,173/100cm3
The solubility for Na2CO3 : 21,6g/100cm3
Therefore I wonder if I can calculate this in any way. As I understood it from the NaOH thread all the Ca(OH)2 must not dissolve as it dissolves when
the reaction is taking place to replace the reacted Ca(OH)2.
I don't know if the amount of moles I am going to use is needed and I am more looking for the actual calculations than just an answer. If there is a
way to calculate this at all. Anyways I plan to use 0,01 moles of the Na2CO3 and as the Ca(OH)2 apparently should be in excess i plan to use the same
amount by weight. So 1,06g of both the Ca(OH)2 and the Na2CO3.
Thanks for any help!
P.s How do i know if my Na2CO3 is anhydrous?
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Nicodem
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Quote: Originally posted by Oggas  | | I want to make NaOH by reacting Na2CO3 with Ca(OH)2. So i need to know how much water i need in order to dissolve both the Na2CO3 and the Ca(OH)2 in
order to make an as concentrated NaOH solution as possible. |
It's a heterogeneous reaction, so you can't calculate anything as Ca(OH)2 will not all dissolve and the product CaCO3 is practically insoluble (that's
why it works at all). The concentration of the resulting NaOH(aq) and reaction conditions in general is only a matter of your filtration equipment.
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ScienceSquirrel
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Really you want to have a look at the literature.
This reaction was carried out by stirring milk of lime which is a supension of calcium hydroxide in water with sodium carbonate solution.
The resulting thick suspension of calcium carbonate in sodium hydroxide solution was then filtered and concentrated.
You are going to need a good vacuum filter to make any headway.
Sodium hydroxide is readily available and cheap so it is a waste of time on a preparative scale.
You can do it on small scale with dilute solutions and gravity filtration but the result will not be very concentrated.
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Oggas
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Thanks for the answers! Mr ScienceSquirrel, would it be possible to make a solution with 0,02 moles NaoH in it? Because what i am looking for is not
that concentrated. And i know it is available as a draincleaner. However the NaOH i bought was only at a concentration of <30% which i discovered
only after i bought it. You'd think it be easier to try and purify the NaOH i have bought. And do you have any idea's on how. I have one idea but i
don't know how successful i will be. I don't know if 0,1 Molar is counted as concentrated but it would do for my purposes.
Anyways, thanks!
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ScienceSquirrel
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You would be talking about using a few grams per litre of calcium hydroxide and sodium carbonate to make a 0.1M solution and I suspect that would
work.
You could probably add the calcium hydroxide to say 450ml of water in a 1 litre PET bottle shake very well to get as much to dissolve and make as fine
a supension as possible, then add the sodium carbonate in 50ml of water.
Shake vigorously and then allow to settle and pour off the supernatant through a coffee filter.
It would not be the best sodium hydroxide solution in the world but it would be OK for most things.
[Edited on 24-5-2011 by ScienceSquirrel]
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