gabriel.rb15
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Purifying NaOH
I'm making NaOH by sea water electrolysis, but i want to purify it from the other salts (like NaCl). Which solvents can i use for it? Is ethanol a
good option?
(sorry for the poor english)
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NEMO-Chemistry
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I think ethanol does react but its one of those reversible things. Do a google for it, also take a look at the PKa of both.
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j_sum1
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Umm. Why?
If you are after NaOH and cannot get it another way then why not start with more pure NaCl?
If you are beginning with salt water then your best bet would be to purify through several recrystallisations to get rid of the potassium and
magnesium cations as well as the sulfate, bromide and iodide anions as well as the assorted organic junk. Do that before you begin electrolysis.
If your interest is in sea water and separating it out, then again, I am not sure why you would attempt electrolysis as a first step.
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gabriel.rb15
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Quote: Originally posted by j_sum1  | Umm. Why?
If you are after NaOH and cannot get it another way then why not start with more pure NaCl?
If you are beginning with salt water then your best bet would be to purify through several recrystallisations to get rid of the potassium and
magnesium cations as well as the sulfate, bromide and iodide anions as well as the assorted organic junk. Do that before you begin electrolysis.
If your interest is in sea water and separating it out, then again, I am not sure why you would attempt electrolysis as a first step.
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This is a project to encourage children and teenagers to learn Chemistry. I can make it the hard way, with a lot of steps, but I THINK it will
discourage them. Another problem is that here the schools don't have a chemistry lab, and glassware in brazil are pretty expensive, so i'll have to
lend my equipment, which are not many.
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gabriel.rb15
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Thanks. I'll take a look.
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LearnedAmateur
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Methanol reacts to form sodium methoxide which is freely soluble in methanol. Assuming you only have a mixture of hydroxide and chloride, you should
be able to carry this out and the NaCl (sol. = 1.5g/100mL @ STP) should remain as a solid. After work up and removal of solvent, the methoxide is
distilled as aqueous solution to remove methanol (B.P. = 64.7C @ 1atm). This should leave you with relatively pure hydroxide as an aqueous solution,
but expect some contamination. Boiling down the solution then heating the wet solid in a crucible will decompose any carbonate that may have formed,
which will be inevitable since it reacts quite rapidly with atmospheric CO2 and water vapour.
In chemistry, sometimes the solution is the problem.
It’s been a while, but I’m not dead! Updated 7/1/2020. Shout out to Aga, we got along well.
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j_sum1
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| Quote: | | This is a project to encourage children and teenagers to learn Chemistry. I can make it the hard way, with
a lot of steps, but I THINK it will discourage them. Another problem is that here the schools don't have a chemistry lab, and glassware in brazil are
pretty expensive, so i'll have to lend my equipment, which are not many. |
Ok makes sense. Well, in that case I don't really see why you need to purify it. This seems to be an exercise in performing some basic chemistry
using natural resources and in capturing the imagination of your students. You start off with sea water. you run a current through it. You see some
bubbles. You end up with a solution that changes the colour of your indicator. You run the students through the theory of what has happened and make
a case for the alkalinity being from NaOH. And then you have a discussion on the range of impurities that might be present and what may be done about
it. If the students' interest goes in that direction you follow up with a purification exercise. If not, you leave it.
[Edited on 5-11-2017 by j_sum1]
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vmelkon
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I imagine that sea water has a lot of Mg(2+). I have that data in my files at home. You can add some Na2CO3 solution and precipitate MgCO3 and filter
with filter paper.
If you do electrolysis of sea water, I guess the OH- formed would precipitate with the Mg as MgCO3.
There is a table here
Total Molar Composition of Seawater (Salinity = 35)
https://en.wikipedia.org/wiki/Seawater
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