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Registered Member #99
Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637
Hello 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!
Registered Member #69
Joined: Thu Feb 09 2006, 07:42AM
Location:
Posts: 116
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...
Registered Member #65
Joined: Thu Feb 09 2006, 06:43AM
Location:
Posts: 1155
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.
Registered Member #99
Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637
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
Registered Member #191
Joined: Fri Feb 17 2006, 02:01AM
Location: Esbjerg Denmark
Posts: 720
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.
Registered Member #193
Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022
*****! 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.
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Preparing solutions from anhydrous forms
