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Quantity of substance

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movies:
I would be surprised if our balance is really as accurate as it's supposed to be.  There are a lot of things that can cause it to drift.  I read a short article once that studied the effect of weighing a flask with a magnetic stir bar in it, with the stir bar in different orientations.  The range of masses was like 20 mg.

And we also have a pretty strong air current in our labs, what with all the fume hoods.  The balance has glass doors on each side, but I don't think they work all that well.

ssssss:

--- Quote from: movies on August 03, 2004, 01:52:46 PM ---I would be surprised if our balance is really as accurate as it's supposed to be.  There are a lot of things that can cause it to drift.  I read a short article once that studied the effect of weighing a flask with a magnetic stir bar in it, with the stir bar in different orientations.  The range of masses was like 20 mg.

And we also have a pretty strong air current in our labs, what with all the fume hoods.  The balance has glass doors on each side, but I don't think they work all that well.

--- End quote ---


Dont you peaple use ELECTRONIC BALANCES?I thought its only our worst labs and chemistry boards where we use these manual balances.

The problem with this balances is that they are really time consuming.

movies:

--- Quote from: ssssss on August 04, 2004, 09:54:18 AM ---Dont you peaple use ELECTRONIC BALANCES?I thought its only our worst labs and chemistry boards where we use these manual balances.

--- End quote ---

Yes, ours is an electronic balance.  I'm sure they make balances that are much more accurate.  It's pretty standard for experimental chemistry labs to have a balance that is accurate to 0.0001 grams (0.1 mg).

Mitch:
In the end if you measure the difference in masses it really doesn't matter how far the balance has drifted.

movies:
Yeah, but with the magnetic stir bar thing the orientation of the stir bar made a big difference, so it would only be the same if you had the orientation precisely the same.  The short story: don't weigh the stir bar.

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