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Offline .Jaxx

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Question Regarding Molar Mass
« on: May 19, 2014, 07:23:20 PM »
Hey guys,

Let me start off by saying i'm an electrical engineer... I have never taken any courses regarding chemistry so please let me know if I'm wrong about anything. I'm working on a project were I need to smooth the surface of 3D prints. I have been using a technique involving vaporizing acetone with the part in an enclosed chamber, this distributes the acetone along the surface of the part and smooths the edges. Essentially I've wired a relay inline with the power for a rice cooker and just been experimenting with different "on" times. The problem I'm having is that is is getting hot in the chamber and starts melting the part. What I've decided to do it run a pipe from the acetone boiling chamber into another chamber where the part sits... I've been running some numbers on it before I actually spend time building this and have become interested is some of the chemistry. The first thought that came to my mind is that the acetone wont actually run through the pipe because it's denser then air... it will just sit at the bottom of the boiling chamber...

I've looked into "molar mass" which to me looks to be much like density (g/mol)...

So MM of air: 28.97g/mol
MM of acetone: 58.08 g/mol

Therefore my prediction is correct? Is there any way to make this system work?

Offline Arkcon

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Re: Question Regarding Molar Mass
« Reply #1 on: May 19, 2014, 08:38:03 PM »
Briefly, no.  Molar mass is not equivalent to density.  Also, a mixture, like air can't have a molar mass.  It does have a density, and acetone vapor may also have a density you can get from a table.
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Offline Borek

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Re: Question Regarding Molar Mass
« Reply #2 on: May 20, 2014, 02:56:10 AM »
Well, for gases that behave ideally there is a linear dependence between molar mass and density (for a given pressure and temperature), so you are right that comparing molar masses is equivalent to comparing densities.

You are also right that for any mixture of a gases there exist an equivalent molar mass, which is a weighted average of molar masses of all gases present.

But no, molar mass doesn't look like a density - density is per volume, not per mole.

If the acetone boils it produces a huge volume of gas, so it can fill up whatever volume is available, replacing the air.
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