Diluting 18M Sulfuric acid to 6M in a volumetric flask?

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Diluting 18M Sulfuric acid to 6M in a volumetric flask?

Postby revolutionx897 » Thu Sep 24, 2009 2:40 am UTC

Hey, I've been tasked with doing this tomorrow in my AP chem class. I have to make 1 L of 6 M H2SO4 from 18 M concentrate in a volumetric flask tomorrow. From the research I've been doing about this, I'm getting the sense that this will be slightly dangerous. Anyone with some good chem lab experience able to help me out on this one? I don't want to end up with sulfuric acid burns.

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Re: Diluting 18M Sulfuric acid to 6M in a volumetric flask?

Postby BlackSails » Thu Sep 24, 2009 2:44 am UTC

Wear gloves.

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Re: Diluting 18M Sulfuric acid to 6M in a volumetric flask?

Postby Omegaton » Thu Sep 24, 2009 2:46 am UTC

Don't forget the splash goggles. A lab coat too if you want to be really careful.

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Re: Diluting 18M Sulfuric acid to 6M in a volumetric flask?

Postby masher » Thu Sep 24, 2009 4:04 am UTC

use a funnel.

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Re: Diluting 18M Sulfuric acid to 6M in a volumetric flask?

Postby Carnildo » Thu Sep 24, 2009 4:07 am UTC

"Do as you oughta: add water to acid". Or was it the other way around?

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Re: Diluting 18M Sulfuric acid to 6M in a volumetric flask?

Postby ST47 » Thu Sep 24, 2009 4:14 am UTC

I'm pretty sure it's the other way around. Say it in an accent so 'waata' rhymes with 'oughta'.

And by pretty sure, I mean absolutely sure. That way water splashes on you and you get wet rather than acid splashes on you and you get burned.

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Re: Diluting 18M Sulfuric acid to 6M in a volumetric flask?

Postby Phoenix112358 » Thu Sep 24, 2009 5:02 am UTC

Yeah, definitely add the acid to the water.

Water expands in volume like 1000 times (well, that's the value our teacher gave us - dunno if he was exxagerating) when it vaporises, so there's a big risk of it causing the acid to fly up and burn you and stuff.

By curiousity, M is the same as the IUPAC mol L-1, right?

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Re: Diluting 18M Sulfuric acid to 6M in a volumetric flask?

Postby Tass » Thu Sep 24, 2009 6:07 am UTC

Phoenix112358 wrote:Yeah, definitely add the acid to the water.


Yes. This. But above all pour slowly! Then if you start to see some boiling, pause and let it cool. If you just pour one into the other in one big swoop, then the the destinction of what went into what doesn't matter so much, they simply got mixed (and will be spluttering and boiling). If you slowly pour the acid into the water and watch it as you go, then you should be safe.

Phoenix112358 wrote:Water expands in volume like 1000 times (well, that's the value our teacher gave us - dunno if he was exxagerating) when it vaporises, so there's a big risk of it causing the acid to fly up and burn you and stuff.


Sounds about right.

Phoenix112358 wrote:By curiousity, M is the same as the IUPAC mol L-1, right?


Yes.

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Re: Diluting 18M Sulfuric acid to 6M in a volumetric flask?

Postby Think » Thu Sep 24, 2009 6:18 am UTC

Wear something that you don't like very much. If any of that acid gets on your clothes, then the next time you run it through the wash, you'll have some nice holes in your shirt or jeans. And keep your face away from the fumes, smelling that stuff's never fun.

Other than that, don't sweat it too much man.

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Re: Diluting 18M Sulfuric acid to 6M in a volumetric flask?

Postby Tass » Thu Sep 24, 2009 6:23 am UTC

Think wrote:Wear something that you don't like very much. If any of that acid gets on your clothes, then the next time you run it through the wash, you'll have some nice holes in your shirt or jeans. And keep your face away from the fumes, smelling that stuff's never fun.

Other than that, don't sweat it too much man.


Agreed. I once spilled concentrated sulphuric acid on my jeans. I removed them quickly and put my legs under the tap. The jeans got holes and discoloration, but my skin took no serious, and no lasting damage.

The stuff is dangerous, but it is not that dangerous.

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Re: Diluting 18M Sulfuric acid to 6M in a volumetric flask?

Postby phlip » Thu Sep 24, 2009 7:03 am UTC

Phoenix112358 wrote:Water expands in volume like 1000 times (well, that's the value our teacher gave us - dunno if he was exxagerating) when it vaporises

According to Wikipedia, the density of 100-degree water is 958.4 kg/m3. From the ideal gas formula, the density of 100-degree water vapour is 0.588 kg/m3 (I'm not sure how ideal steam is, but it'll be the right magnitude at the very least). So yeah, about 1000 times. Gasses tend to be a hell of a lot less dense than liquids and solids.

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Re: Diluting 18M Sulfuric acid to 6M in a volumetric flask?

Postby heydonms » Thu Sep 24, 2009 7:52 am UTC

You can also use a glass rod to reduce splashing.

Rather than just tipping from one container into another and letting the acid fall, you put a glass rod in or just above the container that you are pouring in to (use a retort stand if you like) and pour the acid slowly onto the rod.

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Re: Diluting 18M Sulfuric acid to 6M in a volumetric flask?

Postby mieulium » Thu Sep 24, 2009 1:25 pm UTC

Wait, normally if its that high, they would start off with crystals instead of acid, wouldn't it? And is the teacher serious? 18 M is a really high concentration... for a school.

2M was good enough to make three holes in my jeans, and irritated my skin non-stop after that. I quickly rubbed hand sanitizer on the spot. I don't know whether that helped.

Which comes to the moral of the story kids, WEAR JEANS AND CLOSED TOE SHOES (AND YES, BALLET FLATS ARE STUPID IN A LAB). In my uni they refuse to let you inside the lab when they think that its inadequate.
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Re: Diluting 18M Sulfuric acid to 6M in a volumetric flask?

Postby heydonms » Thu Sep 24, 2009 1:54 pm UTC

mieulium wrote:Wait, normally if its that high, they would start off with crystals instead of acid, wouldn't it?


Only if the lab was quite cold. Sulfuric is liquid at STP.

mieulium wrote:And is the teacher serious? 18 M is a really high concentration... for a school.


It does seem a little unusual to give concentrated acid to someone who feels the need to get handling suggestions from the internet, but maybe he has just been skipping class or something.

mieulium wrote:I quickly rubbed hand sanitizer on the spot. I don't know whether that helped.

Probably not. I'm fairly sure we kept bicarb soda around when working with strong acids at school which would probably be a bit more effective.

I was making CuCl2 from HCl and CuO the other day and a big bucket of water with a box of bicarb balanced beside it were first on my list of requirements.

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Re: Diluting 18M Sulfuric acid to 6M in a volumetric flask?

Postby Sungura » Thu Sep 24, 2009 1:59 pm UTC

Tass wrote:
Think wrote:Wear something that you don't like very much. If any of that acid gets on your clothes, then the next time you run it through the wash, you'll have some nice holes in your shirt or jeans. And keep your face away from the fumes, smelling that stuff's never fun.

Other than that, don't sweat it too much man.
Agreed. I once spilled concentrated sulphuric acid on my jeans. I removed them quickly and put my legs under the tap. The jeans got holes and discoloration, but my skin took no serious, and no lasting damage.

The stuff is dangerous, but it is not that dangerous.
Depends on the acid. Something like sulfuric acid won't penetrate the skin as quickly as, say, hydrochloric acid. So you have a bit more time with sulfuric acid to get it off and that's why you weren't badly burned. Then you have some random acids you don't think of as being dangerous (ex: methanesulfonic acid) but if you get it on you GET IT OFF NOW even at lower concentrations. (My friend spilled maybe 5 mL or so of this on herself, at I believe a 2M concentration, and she was badly burned by the time she got her jeans off they were in shreds and the dye of the jeans burned into her skin - she still had a huge blue patch on her upper thigh from it. This incident was a rush-to-the-ER trip, obviously.)

So do respect anything in the lab, and be careful. Don't be nonchalant or unconcerned because that is when you get lazy, and when you get lazy is when you make mistakes and get sloppy, and that is when most accidents happen.

Oh, and ALWAYS ADD ACID TO WATER. It is a very exothermic reaction and if you do it the other way around, you have really super concentrated acid which runs the risk of boiling over/splashing/etc when you add the tiniest bit of water. If you do it the proper way - adding acid to water - you dilute out the acid as you go so there is a much less violent reaction and it stays controlled. With that volume & concentration, do add it slowly, and if you feel the flask getting hot, let it sit for a bit before adding more. And it will get hot. Definitely do it in a fume hood too. Wear splash goggles, gloves, and a lab coat. For sulfuric acid, latex gloves are more resistant than nitrile.
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Re: Diluting 18M Sulfuric acid to 6M in a volumetric flask?

Postby sgt york » Thu Sep 24, 2009 2:08 pm UTC

Johnny was a chemist's son,
But Johnny is no more.
For what he thought was H2O
Was H2SO4.

And yes, Always Add Acid. Diluting acid in water is exothermic. Adding the small volume of acid to the large volume of water gives the heat more mass to spread out in, making the increase in temperature less, making the risk of a boilover lower.

But really, H2SO4 isn't that big of a deal, as far as acids go. I don't suggest making cocktails with it, but don't stress about it too much.

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Re: Diluting 18M Sulfuric acid to 6M in a volumetric flask?

Postby opsomath » Thu Sep 24, 2009 4:31 pm UTC

With all due respect (no disrespect intended to the OP, who is a student and just following orders) this is a dumb experiment and a bad idea. See, it's like this. Mixing similar amounts of conc. sulfuric acid and water is massively exothermic. Therefore, you should do it slowly, by adding the acid to the water, while stirring rapidly in a container AT LEAST TWICE THE VOLUME YOU ARE TRYING TO PREPARE if not more. Obviously, that is impossible if you are making this up in a volumetric flask, since they contain exactly the target volume plus a bit of airspace at the top.

Offhand, I don't think it's a good idea to prep anything greater than maybe 2M acid directly in the flask. If you need that much approx. 6M acid of a precisely known concentration, make it in a big beaker with approximate volumes and titrate it afterwards.

Full disclosure: I am a senior PhD student in chemistry; organic chemistry, so I don't make a lot of stock acid solutions of known concentration but I work with H2SO4 a lot and have a great deal of respect for its acidyness.

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Re: Diluting 18M Sulfuric acid to 6M in a volumetric flask?

Postby ducksan » Thu Sep 24, 2009 5:11 pm UTC

Sulfuric acid simply loves hydrogen bonding to water, which there isn't much of at all in the fully concentrated stuff. When any bond is formed, heat is released, and the H-bonds that are worth about ~5-10% of a normal bond (between the atoms in question) represent a good deal of heat let out when they happen.
The famous demonstration of sugar and sulfuric acid is one of the most vicious - H2SO4 will destroy the sugar molecule, pulling out the equivalent of six molecules of water per hexose used. It's that "thirsty".The remains of the sugar are basically elemental carbon, assuming the reaction goes to completion.

The acid destroys clothing because it's such a damn good hydrolysis catalyst. (It also helps with condensation, the same reaction going in the opposite direction, but that's not relevant here.) Cotton is a polysaccharide, and polyester is exactly what it says on the tin. I know both would break down nicely in acid, not sure about other fabrics or materials.

In other news, the advice in this thread is sound. Large beaker, all safety precautions, slowly add the acid to water. Stirring will cool it down.
Make sure you've done the proper calculations as to exactly how much you'll need. It may or may not be possible to do this in smaller batches and combine them, but I'm not too experienced here.
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Re: Diluting 18M Sulfuric acid to 6M in a volumetric flask?

Postby meat.paste » Thu Sep 24, 2009 5:26 pm UTC

opsomath wrote:Therefore, you should do it slowly, by adding the acid to the water, while stirring rapidly in a container AT LEAST TWICE THE VOLUME YOU ARE TRYING TO PREPARE if not more. Obviously, that is impossible if you are making this up in a volumetric flask, since they contain exactly the target volume plus a bit of airspace at the top.


Very good point. Start with about 500 mL of water in a 2L beaker with a stir bar in the bottom. SLOWLY add the correct amount of H2SO4 (333.3 mL by my calculation). Keep the temperature down. This much acid into water should take at least 15 minutes. SLOWLY!!!

Take the resulting solution (after it has cooled down) and transfer it quantitatively to the volumetric flask. I.e., pour it without spilling, then (rinse the beaker out with water and pour that in the volumetric flask) x3. Use DI water (obvious, I hope). You should now have a volumetric flask that is about 50 mL of water short of being correctly filled. Fill it appropriately (don't forget to occasionally stir the mix).

By the way, the use of a volumetric flask implies you are trying to get something like 6.00 (+/- 0.01) M solutions. If you are planning to titrate it afterwards to determine the exact concentration, then skip the volumetric flask entirely and make a 6.0 +/- 0.1 M solution (327-339 mL of conc. H2SO4) in the beaker. It'll be good enough.
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Re: Diluting 18M Sulfuric acid to 6M in a volumetric flask?

Postby kernelpanic » Thu Sep 24, 2009 9:51 pm UTC

mieulium wrote:Wait, normally if its that high, they would start off with crystals instead of acid, wouldn't it? And is the teacher serious? 18 M is a really high concentration... for a school.

Why? in my school we sometimes use 36 (or was it 26?) M HCl and while we do use special protection (full face "shield" instead of lab goggles, lab coat, etc.) it's not a big deal. We have also handled Cl2...
As long as you use common sense, you'll be OK.
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Re: Diluting 18M Sulfuric acid to 6M in a volumetric flask?

Postby Ingolifs » Thu Sep 24, 2009 10:33 pm UTC

(ex: methanesulfonic acid) but if you get it on you GET IT OFF NOW even at lower concentrations. (My friend spilled maybe 5 mL or so of this on herself, at I believe a 2M concentration, and she was badly burned by the time she got her jeans off they were in shreds and the dye of the jeans burned into her skin - she still had a huge blue patch on her upper thigh from it. This incident was a rush-to-the-ER trip, obviously.)


Wow. Had no idea that methanesulfonic acid was that nasty.

The nastiest stuff I work with is probably Phosphorus oxychloride. Working with it today if everything goes to plan.
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Re: Diluting 18M Sulfuric acid to 6M in a volumetric flask?

Postby ducksan » Thu Sep 24, 2009 11:34 pm UTC

kernelpanic wrote:...Why? in my school we sometimes use 36 (or was it 26?) M HCl...
As long as you use common sense, you'll be OK.


Hydrochloric acid goes no higher than 12-13 M in water. You'd have to liquefy the gas to get more of it in one place, presumably.

Also, does anyone know what the pKa of methanesulfonic acid is? I wonder why it's so caustic.
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Re: Diluting 18M Sulfuric acid to 6M in a volumetric flask?

Postby Alexius » Fri Sep 25, 2009 11:08 am UTC

sgt york wrote:Johnny was a chemist's son,
But Johnny is no more.
For what he thought was H2O
Was H2SO4.

And yes, Always Add Acid. Diluting acid in water is exothermic. Adding the small volume of acid to the large volume of water gives the heat more mass to spread out in, making the increase in temperature less, making the risk of a boilover lower.

Thus the other sulfuric acid rhyme:
May her rest be long and placid
She added water to the acid
The other girl did what we taught 'er
And added acid to the water.

To second other people's advice: Lab coat, goggles (even if you wear glasses, put goggles on over them) and gloves. Pour VERY SLOWLY- what I would do is put the concentrated acid in a tap funnel, and do it drop by drop. It may also be an idea to put your container (not a volumetric flask) in a big bath of ice water.

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Re: Diluting 18M Sulfuric acid to 6M in a volumetric flask?

Postby opsomath » Fri Sep 25, 2009 1:50 pm UTC

ducksan wrote:
kernelpanic wrote:
Also, does anyone know what the pKa of methanesulfonic acid is? I wonder why it's so caustic.


Your wish has been granted!

http://www.chem.wisc.edu/areas/reich/pkatable/

pKa = 1.6 according to this. Several orders of magnitude less acidic than sulfuric acid; however, that is still plenty acidic enough to protonate all sorts of stuff in your soft tissues that should not be protonated. I strongly suspect that the greater damage potential of methanesulfonic acid is due to its lower polarity and corresponding ability to diffuse into your fatty tissues and damage you directly rather than having to corrode its way in like sulfuric acid does. A lot of organic materials are like that; they aren't that reactive on paper, but they will certainly mess you up on contact because your skin is good at keeping out highly polar contaminants like aqueous solutions, but not so good at keeping out powerful organic solvents. See also DMSO, which can not only diffuse right into your skin but also take other things with it; also aniline and phenol, which are in the elite category of organic compounds for which it is easily possible to absorb enough from a spill on your skin to kill you.

Spell checker does not like "protonate" and "methanesulfonic." Protonate. Protonate. Protonate. Thass right.


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