Neal
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Does anyone here do reverse osmosis at home?
If so, how small can you go, diameter-wise? Or any of the other procedures for removing stuff from solution.
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Neal
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Okay here's a question.
Suppose you have a bowl of water with salt and sugar in it. How would you suck out the salt without the sugar, or suck out the sugar without the salt?
I think the answer is reverse osmosis. 1st reverse osmosis the salt because it is smaller than sugar. Then, reverse osmosis a larger size, for the
sugar. So the order matters.
If you reverse osmosis the sugar 1st, then you're also sucking in the salt.
O, and if the salt and sugar crystals are both the same size, you stir the water so the salt dissolves more.
My question is, how small can 1 reverse osmosis in their own lab? Or any other similar procedures?
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Rainwater
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Ok. I see where you are heading.
I'm assuming your understanding of reverse osmosis is similar to the following
A membrane is used to seperate 2 liquids, kinda like a filter, small stuff can pass, larger things can not.
So water(small) can pass but salts(big) and other materials get stuck in the filter and don't make it through.
That's not how the design of the membrane works. But it is a part of it.
Nerdrage can explaine it a lot better than I can, but here is my understanding
2 volumes of liquid, at equal pressure, connected by a membrane will defuse into each other, until the consentration of each are equal. (Nature likes
to be balanced)
For example, two cups, #1 containing salt water and #2 only water. The salt, in dissolved state forms weak bonds with the water, the water stick to
the salt making it much bigger that it is, the effect is that it can not pass through the membrane, so the water from cup 2, flows into cup 1 to
attempt to diluted the consentration to reach a pressure equilibrium. The effect is cup #2 flows into cup #1
This is the osmosis effect.
By increasing the pressure in cup #1 relative to cup #2 the pressure equilibrium is shifted so the cup #1 needs to increase its consentration of salt
relative to cup #2, so water flows from #1 into #2 and the salt stays behind.
| Quote: | | any of the other procedures for removing stuff from solution. |
Precipitation, recrystallization, and extraction would apply here
Edit:
https://youtu.be/Nb1w15DHO4g
Time index 12:00
[Edited on 16-12-2022 by Rainwater]
"You can't do that" - challenge accepted
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Neal
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How do you increase the pressure of a cup? Or sealed chamber?
Anyways, our body does something similar. Our urine is salty. Urine is 95% water, then urea is the next largest. After that, are sodium, potassium,
and chloride ions.
But as we know, eating sweet stuff does not make our urine salty. That means, sugar is excreted the other route. So therefore somewhere in out body it
separates salts and sugars, salts going to the urine.
But salt can only be ionic, and sugar only covalent. Though some sugars have have some ionic within covalents. Sugar is mostly eaten by enzymes such
as insulin and glucagon, throughout the body. Salt is mostly absorbed in the intestines with water. But kidneys have a filtration process for sodium
ions. Ultrafiltration in the kidney, in the glomerulus, which prevents bigger things like proteins going through, but says even anions have a hard
time going through.
So it appears to me that in the body, sugar is separated out 1st, then salt. So we can never have sweet urine. Unless something sweet can be ionic.
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Neal
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Besides osmosis and reverse osmosis (filtrating the small from the big), there's this answer I got on the opposite: filtrating the big from the small.
I think it should be possible to make a membrane that blocks salt but allows sugar through too, based on the charge of sodium or chloride ions. You
only have to block one of them, the other ion will be blocked by the electric field after a few have diffused to the other side. Or there may be some
solvent in which salt or sugar dissolves, but the other doesn't. Solubility of sugars in water is generally better than the solubility of kitchen salt
(you didn't mention exactly what sugar and salt you're dealing with), so by concentrating the solution you may be able to get the salt out, partially
at least. Or evaporate the water, melt the sugar and filtrate (or does salt dissolve in molten sugar?), but that risks pyrolysis of sugar. Or
evaporate the water and try to get giant crystals of sugar and salt, which can be separated by hand. Or try some chemistry trick to replace the
chloride ions by some other ion, then try one of the above tricks. But a filter based on size sounds simplest and may be commercially available.
Probably still not worth the effort, though.
[Edited on 20-12-2022 by Neal]
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