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Author Topic: How much magnesium sulfate do I add to make 8 mL anhydrous acetone?  (Read 5402 times)

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CapnBlubs

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My mentor gave me a protocol saying he simply "added magnesium sulfate to 8 mL acetone, mixed, and allowed to settle overnight." It doesn't say how much magnesium sulfate, nor any other potentially important details, and I won't be able to ask him until Monday and kind of need to get the procedure that involves this acetone done this weekend. Can anyone help out? Thanks.
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macman104

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Re: How much magnesium sulfate do I add to make 8 mL anhydrous acetone?
« Reply #1 on: April 03, 2009, 02:06:48 PM »

Is this procedure part of a reaction, or is this all you are supposed to do?  I've never heard of magnesium sulfate being added to acetone.

MgSO4 is usually added in its anhydrous form to organic solvents to remove trace amounts of water left in them.  If this is the case, you need to add MgSO4 and swirl it in the acetone.  Keep adding sulfate until the powder becomes free flowing.  If it is clumping up, then it has absorbed water.

If that's not what this is for, then I'm clueless.
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CapnBlubs

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Re: How much magnesium sulfate do I add to make 8 mL anhydrous acetone?
« Reply #2 on: April 04, 2009, 11:33:31 AM »

What you described sounds like exactly what I need.  I guess my wording wasn't clear enough and I left out the key word anhydrous before magnesium sulfate - we have acetone and I have to prepare anhydrous acetone (for use in a fatty acid methylation reaction with iodomethane) by adding anhydrous magnesium sulfate, mixing and leaving overnight.

Not having done that before, I just wasn't sure if there was a specific amount that would be needed to do the job or if there would be an obvious change that would tell me when I'd added enough.  Although I'm still not 100% sure what it'll look like at least I've got enough of an idea to give it a shot.  Thanks.
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Arkcon

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Re: How much magnesium sulfate do I add to make 8 mL anhydrous acetone?
« Reply #3 on: April 04, 2009, 12:41:25 PM »

I suppose you could try to estimate how much moisture is in the acetone, and try to add a stoichiometric amount of anhydrous salt.  But to tell the truth, I've never known anyone who's gone to that much trouble.  Once, during organic chem class, I added a small amount of anhydrous salt to dry my product, and instead of just sitting there, absorbing the moisture, like every other time, it crystallized into a mass of clear Epsom salt crystals, eating up a chuck of my product.  And all my teacher had to say about it was "Oh, you should have distilled first."  Yeah, well, thanks ... for telling me now.  SO you see, sometimes, people just aren't as exact as you'd expect they'd be, given the specificity of the rest of the procedure.  It just happens that way.
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CapnBlubs

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Re: How much magnesium sulfate do I add to make 8 mL anhydrous acetone?
« Reply #4 on: April 04, 2009, 01:48:00 PM »

Heheh...the classic situation where a teacher realizes a mistaken or omitted direction but refuses to admit it for fear of showing weakness.  And I'd know, because as a teaching assistant I've had a few of those moments myself.

And I agree on the exactness thing.  Applies to safety too.  You'll have some lab procedures that are unbelievable overkill and some that don't go nearly far enough.
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gfunk

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Re: How much magnesium sulfate do I add to make 8 mL anhydrous acetone?
« Reply #5 on: April 04, 2009, 08:15:13 PM »

Drying chemicals with drying salts is quite qualitative.  Choice of salt is also important.
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Arkcon

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Re: How much magnesium sulfate do I add to make 8 mL anhydrous acetone?
« Reply #6 on: April 05, 2009, 04:49:28 AM »

Heheh...the classic situation where a teacher realizes a mistaken or omitted direction but refuses to admit it for fear of showing weakness. 

Just a heads up, that wasn't really true in this case.  My product shouldn't have been so contaminated with water, I can't recall what I'd done wrong, but it really was my own shortcoming.  So, if your acetone has been mixed 1:10 with water, then you may lose lots adding anhydrous salt.  But then, you should be using a fresher bottle, anyway.
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