Preparing solutions from anhydrous forms
EEYORE, Fri Aug 18 2006, 02:48AMHello all,
Ive been googling all day and cant find a solution. I have some anhydrous methanol coming in the mail for my fuel cell project. From googling, I see that this anhydrous methanol is dry? So, how do I prepare a 3% solution of methanol from anhydrous methanol?For future reference, how does one go about doing this for all anhydrous forms of compounds? I could figure it out if the application called for a molar concentration...Or, is this simply that?Im so confused!Please help!
Thanks!
Matt
Re: Preparing solutions from anhydrous forms
Eric, Fri Aug 18 2006, 03:31AM
It's a pet peeve of mine that when percents are thrown around people rarely specify whether it is a w/w, w/v or v/v percentage. So, it depends!
I would guess that it's w/w in which case you would need 3g of methanol for 97g of water. Actually, it might be v/v in which case you'd take 3 parts by volume and water it down to 100 parts. Both ways end up giving almost the same result...
Eric, Fri Aug 18 2006, 03:31AM
It's a pet peeve of mine that when percents are thrown around people rarely specify whether it is a w/w, w/v or v/v percentage. So, it depends!
I would guess that it's w/w in which case you would need 3g of methanol for 97g of water. Actually, it might be v/v in which case you'd take 3 parts by volume and water it down to 100 parts. Both ways end up giving almost the same result...
Re: Preparing solutions from anhydrous forms
Carbon_Rod, Fri Aug 18 2006, 04:00AM
Molarity can be adjusted – and most labels will show the M instead of %.
But usually molar concentration is initially calculated from weight, as a chemist’s most precise tool is usually the scale (assuming the material is known to be stable in the atmosphere.)
I don’t think it will matter much with that concentration – as IIRC the potassium hydroxide solution is likely going to be absorbing moisture and CO2 from the atmosphere anyways.
Carbon_Rod, Fri Aug 18 2006, 04:00AM
Molarity can be adjusted – and most labels will show the M instead of %.
But usually molar concentration is initially calculated from weight, as a chemist’s most precise tool is usually the scale (assuming the material is known to be stable in the atmosphere.)
I don’t think it will matter much with that concentration – as IIRC the potassium hydroxide solution is likely going to be absorbing moisture and CO2 from the atmosphere anyways.
Re: Preparing solutions from anhydrous forms
EEYORE, Fri Aug 18 2006, 04:30AM
Yea, fuelcellstore isnt too helpful. When I asked them , they just responded that it must not be over "3% methanol in solution...We sell 100mL of 3% methanol..."
I will just bet on it being weight...
Matt
EEYORE, Fri Aug 18 2006, 04:30AM
Yea, fuelcellstore isnt too helpful. When I asked them , they just responded that it must not be over "3% methanol in solution...We sell 100mL of 3% methanol..."
I will just bet on it being weight...
Matt
Re: Preparing solutions from anhydrous forms
Bored Chemist, Fri Aug 18 2006, 06:07AM
I would bet on it being by volume because it's easy to measure and accuracy doesn't matter much here.
Bored Chemist, Fri Aug 18 2006, 06:07AM
I would bet on it being by volume because it's easy to measure and accuracy doesn't matter much here.
Re: Preparing solutions from anhydrous forms
Electroholic, Fri Aug 18 2006, 04:53PM
you cannot do it as Eric said.
Methanol and Water dissolves into each other.
say you add half a cup of sugar into a L of water,
you will still end up with 1L of solution.
same thing goes with methanol and water.
although the effect is not as strong.
I remember doing an experiment at school, where we mixed 500ml of ethanol with 500ml of water.
and we ended up with quite a bit less.
Electroholic, Fri Aug 18 2006, 04:53PM
you cannot do it as Eric said.
Methanol and Water dissolves into each other.
say you add half a cup of sugar into a L of water,
you will still end up with 1L of solution.
same thing goes with methanol and water.
although the effect is not as strong.
I remember doing an experiment at school, where we mixed 500ml of ethanol with 500ml of water.
and we ended up with quite a bit less.
Re: Preparing solutions from anhydrous forms
Bored Chemist, Fri Aug 18 2006, 10:50PM
*****!
Look! It really won't matter that much.
All of the good folk pointing out the problems are quite correct. It isn't a trivial question.
It won't practically speaking matter.
Feel free to look up stuff about "partial molar volumes".
The answer to the original question is ( so far as it matters ) take a couple of tablespoons of methanol and make it up to a litre with water.
Bored Chemist, Fri Aug 18 2006, 10:50PM
*****!
Look! It really won't matter that much.
All of the good folk pointing out the problems are quite correct. It isn't a trivial question.
It won't practically speaking matter.
Feel free to look up stuff about "partial molar volumes".
The answer to the original question is ( so far as it matters ) take a couple of tablespoons of methanol and make it up to a litre with water.
Print this page