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Chemosynthesis
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Quote: Originally posted by Trizocy  |
"Molarity is usually more important to a chemist than percentage"
- May i ask why? would it not be better to say: yup this bottle is 100% acid ? than 281/mols in it  ? |
Molarity is more important, generally, because that makes reactions easier to express. When you write a reaction, you consider equivalents of
reactants, like X molecules of reactant A combining with Y molecules of reactant B. Moles are directly proportional to molecules.
If you wanted to use mass, you'd need to start converting more units again because they are not equivalent in the same way. This takes time and might
introduce calculation errors.
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Volanschemia
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| Quote: Originally posted by Trizocy | Hmm, interesting.
"Is it just a portable meter or a computerized one?"
- Its a portable, with temp and ph meter
"Molarity is usually more important to a chemist than percentage"
- May i ask why? would it not be better to say: yup this bottle is 100% acid ? than 281/mols in it ?
Thanks, waiting for the ph meter to arrive, so gonna do a try, will keep you updated  |
Yeah, with a portable indicator, it is a good idea to calibrate it every time you use it. Did you also purchase a buffer solution?
Well, percentage is useful for getting an idea of the concentration at a glance but you need Molarity to figure out how much of a certain reagent you
need for a certain reaction.
For example, if you want to make 100g of NaCl from reacting HCl and NaOH (pretty stupid reaction I know, but for an example its nice and easy) you
would need to know how many moles of HCl and NaOH are in each solution so you can work out how much of each you need.
So 1 Mole of HCl reacts with 1 Mole of NaOH. So if you had a 5M solution of NaOH and HCl, well that's easy, you just do equal amounts. But if you
have 10M HCl and 5M NaOH, you would need a 2:1 ratio. In this context, percentages are useless because a 10% solution of HCl and a 10% solution of
NaOH are completely different molarities.
Yeah, keep me updated! I'd like to see how it goes.
[Edit] Heh, Chemosynthesis beat me this time! 
[Edited on 17-2-2015 by TheAustralianScientist]
"The chemists are a strange class of mortals, impelled by an almost insane impulse to seek their pleasures amid smoke and
vapor, soot and flame, poisons and poverty; yet among all these evils I seem to live so sweetly that may I die if I were to change places with the
Persian king" - Johann Joachim Becher, 1635 to 1682.
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j_sum1
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All good stuff here.
Let me reiterate that there are issues with NaOH. It absorbs moisture from the atmosphere and so you never know quite how much you actually have.
You could be up to 10% off easily.
However, Give it a shot anyway. It is one thing to talk about it and swap calculations. It is quite another thing to do it.
In any case, it is common to do a rough titration first to get an approximate value; which makes it simpler to do an accurate one later.
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Trizocy
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| Quote: Originally posted by j_sum1 | All good stuff here.
Let me reiterate that there are issues with NaOH. It absorbs moisture from the atmosphere and so you never know quite how much you actually have.
You could be up to 10% off easily.
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Woot! up to 10%
Nope,
While i was searching for burette i found this one: LINL lets talk about accurate then but quite expensive no need for pipettes,burettes etc etc then
[Edited on 17-2-2015 by Trizocy]
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Volanschemia
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If you dry the NaOH in an oven before dissolving it in solution you shouldn't have any troubles.
You need to get a buffer if you want to get an accurate pH measurement. You should be able to get some online pretty easy. Here is an example but not sure of the quality since it comes from china. A liquid would be better and you should be able to get it from a lab
supplier if you have one nearby.
You also need to keep your pH meter in a solution of KCl or similar when in storage because it can get damaged if the bulb dries out.
A pipette vs a burette would probably only make a difference of 0.5% if that so don't spend on one unless you really need one.
"The chemists are a strange class of mortals, impelled by an almost insane impulse to seek their pleasures amid smoke and
vapor, soot and flame, poisons and poverty; yet among all these evils I seem to live so sweetly that may I die if I were to change places with the
Persian king" - Johann Joachim Becher, 1635 to 1682.
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morganbw
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| Quote: Originally posted by TheAustralianScientist | If you dry the NaOH in an oven before dissolving it in solution you shouldn't have any troubles.
You need to get a buffer if you want to get an accurate pH measurement. You should be able to get some online pretty easy. Here is an example but not sure of the quality since it comes from china. A liquid would be better and you should be able to get it from a lab
supplier if you have one nearby.
You also need to keep your pH meter in a solution of KCl or similar when in storage because it can get damaged if the bulb dries out.
A pipette vs a burette would probably only make a difference of 0.5% if that so don't spend on one unless you really need one. |
Just drying does not fix it completely. Sodium Carbonate is also formed when exposed to the air.
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Trizocy
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Hmm one question,
I got my sulfuric acid in my garage, will it absorbs moisture from the atmosphere over time?
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Molecular Manipulations
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If the container is airtight, then probably not. Keep a good seal and it will do fine, I put Teflon tape around the threads if it's stored for a long
time.
-The manipulator
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Volanschemia
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If you put the NaOH in the oven for just five minutes it will be fine.
I don't think you need a result down to the millimole do you? I highly doubt you will get a margin of error above 1% unless you leave the NaOH out
without a lid for an hour and I think a percentage within 1% was all you needed am I correct?
Since your Sulphuric Acid already seems quite concentrated its hydroscopy will be fairly minimal. Like MM said, and from my own experience, as long
you keep the lid on you shouldn't have any trouble.
Have got looked at pH buffers yet? If you want, you can use a pH indicator like Phenolphthalein with much the same results.
"The chemists are a strange class of mortals, impelled by an almost insane impulse to seek their pleasures amid smoke and
vapor, soot and flame, poisons and poverty; yet among all these evils I seem to live so sweetly that may I die if I were to change places with the
Persian king" - Johann Joachim Becher, 1635 to 1682.
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Molecular Manipulations
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Define "fine". Cause if you think five minutes in an oven at any reasonable temperature will dehydrate sodium hydroxide, you are sadly mistaken.
An hour at 500 deg.C might bring it to 95-97%.
| Quote: |
Since your Sulphuric Acid already seems quite concentrated its hydroscopy will be fairly minimal.
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Umm, say what? The more concentrated the acid, the more hydroscopic it will be. And sulfuric acid is very hydroscopic.
[Edited on 18-2-2015 by Molecular Manipulations]
-The manipulator
We are all here on earth to help others; what on earth the others are here for I don't know. -W. H. Auden
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jsc
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I hope I caught you before you tried this.
Boiling sulfuric acid is a bad idea. What will happen is that a large amount of it will be vaporized. If you do it indoors, those vapors will then
condense on EVERY SURFACE IN THE HOUSE. For example, if you have wallpaper, this will result in large black splotches on the walls, giving it sort of
the "cow" look. It will also rust any and all metal in the house. Also, acids have a tendency to eat through clothes, so you wash your clothes and
there will be holes in them. Also, if you are in the house while those vapors are there you will be breathing those vapors. Get the picture?
At a bare minimum you need some kind of condenser.
A larger problem is that a drain cleaner will have all kinds of crap in it. If you remove water, you will concentrate the crap as well as the acid. To
purify it you have to distill it, a dangerous activity that requires specialized equipment because it has a high boiling point.
You can remove some of the organics by adding a small amount of concentrated hydrogen peroxide (see YouTube).
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Volanschemia
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Fine for a rough titration.
I also don't think that NaOH stored in an airtight container will be 10% water. If that was the case it would be a slush.
My mistake with the Suphuric Acid. You are right there. But if it's kept in an airtight bottle it will be fine. I have had 98% Sulphuric Acid for 6
months now and my last titration showed 97.5% so nothing serious has happened.
"The chemists are a strange class of mortals, impelled by an almost insane impulse to seek their pleasures amid smoke and
vapor, soot and flame, poisons and poverty; yet among all these evils I seem to live so sweetly that may I die if I were to change places with the
Persian king" - Johann Joachim Becher, 1635 to 1682.
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Volanschemia
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| Quote: Originally posted by jsc | I hope I caught you before you tried this.
Boiling sulfuric acid is a bad idea. What will happen is that a large amount of it will be vaporized. If you do it indoors, those vapors will then
condense on EVERY SURFACE IN THE HOUSE. For example, if you have wallpaper, this will result in large black splotches on the walls, giving it sort of
the "cow" look. It will also rust any and all metal in the house. Also, acids have a tendency to eat through clothes, so you wash your clothes and
there will be holes in them. Also, if you are in the house while those vapors are there you will be breathing those vapors. Get the picture?
At a bare minimum you need some kind of condenser.
A larger problem is that a drain cleaner will have all kinds of crap in it. If you remove water, you will concentrate the crap as well as the acid. To
purify it you have to distill it, a dangerous activity that requires specialized equipment because it has a high boiling point.
You can remove some of the organics by adding a small amount of concentrated hydrogen peroxide (see YouTube).
|
Yes, don't boil in the house. I don't think he was planning to though, since he's already determined it's above 90%.
Trizocy, what were you planning on using the acid for?
[Edited on 18-2-2015 by TheAustralianScientist]
"The chemists are a strange class of mortals, impelled by an almost insane impulse to seek their pleasures amid smoke and
vapor, soot and flame, poisons and poverty; yet among all these evils I seem to live so sweetly that may I die if I were to change places with the
Persian king" - Johann Joachim Becher, 1635 to 1682.
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Cou
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| Quote: Originally posted by jsc | I hope I caught you before you tried this.
Boiling sulfuric acid is a bad idea. What will happen is that a large amount of it will be vaporized. If you do it indoors, those vapors will then
condense on EVERY SURFACE IN THE HOUSE. For example, if you have wallpaper, this will result in large black splotches on the walls, giving it sort of
the "cow" look. It will also rust any and all metal in the house. Also, acids have a tendency to eat through clothes, so you wash your clothes and
there will be holes in them. Also, if you are in the house while those vapors are there you will be breathing those vapors. Get the picture?
At a bare minimum you need some kind of condenser.
A larger problem is that a drain cleaner will have all kinds of crap in it. If you remove water, you will concentrate the crap as well as the acid. To
purify it you have to distill it, a dangerous activity that requires specialized equipment because it has a high boiling point.
You can remove some of the organics by adding a small amount of concentrated hydrogen peroxide (see YouTube).
|
Boiling sulfuric acid also releases SO3, which *could* be a carcinogen, especially with long term exposure such as in factory workers. If you
absolutely have to boil sulfuric acid, wear a dual respirator with an SO2 or SO3 filter (not sure if those filters work interchangably). I always use
a respirator when working with chlorine gas and it works wonders.
[Edited on 18-2-2015 by Cou]
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Molecular Manipulations
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Jsc, I don't think he was planning on doing this indoors. What you said is mostly correct, if he was to boil down a bathtub full of
acid, but a few 100's of mL, not so much.
TAC, not slush by a long shot. Any technical grade NaOH you find is less than 90% pure, even 70% would resemble a dry powder or
chips. You do realize that in hydroscopic materials, the water is incorporated in the crystalline structure. Magnesium sulfate hexahydrate has six
water molecules per Mg and SO4 ion, and is about 46% water by weight, but is still dry.
[Edited on 18-2-2015 by Molecular Manipulations]
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Cou
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NEVER MAKE TOXIC GASES INSIDE THE HOUSE. Always use a fume hood or do it outside. And wear a respirator... as fun as chemistry is, I don't think it's
worth going to the doctor 5 years later, and finding out you only have 6 months to live because of cancer. Or pneumonia the day after getting too big
a whiff of SO2 and SO3.
[Edited on 18-2-2015 by Cou]
[Edited on 18-2-2015 by Cou]
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Volanschemia
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| Quote: Originally posted by Molecular Manipulations |
TAC, not slush by a long shot. Any technical grade NaOH you find is less than 90% pure, even 70% would resemble a dry powder or
chips. You do realize that in hydroscopic materials, the water is incorporated in the crystalline structure. Magnesium sulfate hexahydrate has six
water molecules per Mg and SO4 ion, and is about 46% water by weight, but is still dry.
[Edited on 18-2-2015 by Molecular Manipulations] |
As far as I and several others I have conferred with know, NaOH does not hydrate, merely dissolves in the water it pulls in, and it certainly can't be
compared to MgSO4.
"The chemists are a strange class of mortals, impelled by an almost insane impulse to seek their pleasures amid smoke and
vapor, soot and flame, poisons and poverty; yet among all these evils I seem to live so sweetly that may I die if I were to change places with the
Persian king" - Johann Joachim Becher, 1635 to 1682.
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Molecular Manipulations
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Sorry but what you said makes no sense.
Who are these "others"? If it absorbs water then it must hydrate. The water is absorbed for a reason and certainly is incorporated in the crystalline
structor.
It makes NaOH-2H2O and NaOH-3.5H2O.
For it to randomly absorb water without forming a hydrate is beyond ridiculous.
It may not be comparable with magnesium sulfate in the sense that the hydrates are ill-defined and still hydroscopic themselves, but in the sense that
the analogy was used it's comparable as anything.
[Edited on 18-2-2015 by Molecular Manipulations]
-The manipulator
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Amos
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| Quote: Originally posted by Molecular Manipulations | Sorry but what you said makes no sense.
Who are these "others"? If it absorbs water then it must hydrate. The water is absorbed for a reason and certainly is incorporated in the crystalline
structor.
It makes NaOH-2H2O and NaOH-3.5H2O.
For it to randomly absorb water without forming a hydrate is beyond ridiculous.
It may not be comparable with magnesium sulfate in the sense that the hydrates are ill-defined and still hydroscopic themselves, but in the sense that
the analogy was used it's comparable as anything.
[Edited on 18-2-2015 by Molecular Manipulations] |
If dry, dusty soil becomes wet, it surely must be due to water being incorporating it into its crystal structure!
I'm with TheAustralianScientist here, I don't think that NaOH hydrates in the same sense as those compounds that have a well-defined crystal structure
and incorporate water in a set ratio. I'm hesitant to say more with my admittedly small knowledge on the subject, but if you're going to belittle
TheAustralianScientist, why not educate him as well? Pull out the sources.
And how would you explain hygroscopic polymers, activated alumina, etc? Are they forming whole new crystal structures, or merely adsorbing the water
on their surface or within pores?
[Edited on 2-18-2015 by Amos]
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Volanschemia
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Molecular Manipulations, I would be more than happy to admit that I am wrong if you can provide me with evidence that NaOH does indeed hydrate like
you are suggesting.
In fact, I would be happy to have learned something new.
"The chemists are a strange class of mortals, impelled by an almost insane impulse to seek their pleasures amid smoke and
vapor, soot and flame, poisons and poverty; yet among all these evils I seem to live so sweetly that may I die if I were to change places with the
Persian king" - Johann Joachim Becher, 1635 to 1682.
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Molecular Manipulations
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Cause adding water to dirt to make mud is the same as it being absorbed from the air...
I'm on my phone now and posting sources is a pain, if you want them, wait till tomorrow - or find them yourself.
-The manipulator
We are all here on earth to help others; what on earth the others are here for I don't know. -W. H. Auden
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Volanschemia
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| Quote: Originally posted by Molecular Manipulations | Cause adding water to dirt to make mud is the same as it being absorbed from the air...
I'm on my phone now and posting sources is a pain, if you want them, wait till tomorrow - or find them yourself.
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You didn't mention the hydroscopic polymers...
Anyway, I'm happy to wait until tomorrow for sources.
I will be sticking to my opinions though until they have been proven incorrect by a trusted source of information.
"The chemists are a strange class of mortals, impelled by an almost insane impulse to seek their pleasures amid smoke and
vapor, soot and flame, poisons and poverty; yet among all these evils I seem to live so sweetly that may I die if I were to change places with the
Persian king" - Johann Joachim Becher, 1635 to 1682.
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Molecular Manipulations
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Ah what the hell, one little source couldn't hurt for now.
How's this?
And if that's not enough, this picture is clear proof, I got it online, so it must be true:
[Edited on 18-2-2015 by Molecular Manipulations]
-The manipulator
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Bert
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Would you care to describe the oven temperature used for that 5 minutes? Also the container material used?
"Hydroscopy"
HYDROSCOPIC
The word is HYGROSCOPIC. Hydroscopy would be looking into water... using a hydroscope.
Sulfuric acid is QUITE hygroscopic. It's used in desiccators. The more concentrated the acid, the more hygroscopic it will be.
Rapopart’s Rules for critical commentary:
1. Attempt to re-express your target’s position so clearly, vividly and fairly that your target says: “Thanks, I wish I’d thought of putting it
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2. List any points of agreement (especially if they are not matters of general or widespread agreement).
3. Mention anything you have learned from your target.
4. Only then are you permitted to say so much as a word of rebuttal or criticism.
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Amos
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I never said water was purposefully added to the dirt. Very dry dirt when placed in a more humid environment WILL become more moist, and not because
it hydrates, but because water diffuses into anything dry. I was just illustrating how not everything is changing structure and hydrating just because
it captures water.
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