On 5/9/2017 8:29 PM, whit3rd wrote:
On Monday, May 8, 2017 at 6:35:37 PM UTC-7, rickman wrote:
On 5/8/2017 7:56 PM, whit3rd wrote:
On Saturday, May 6, 2017 at 9:21:13 PM UTC-7, wrote:
In orgo labs we used acetone to be sure there was no water left on glassware.

Acetone (spozably) evaporates completely.

There's better for that, though, because acetone is hygroscopic. It
pulls in water from the air. If you can blow off droplets and bake dry afterward, alcohol
is just as good, and less expensive.

Why is that a concern? It is hygroscopic until it forms the azeotrope.
Even that ratio will still dissolve more water into it and the residue
evaporate readily. No need to blow drops off, acetone is very thin and
in a few seconds evaporates totally.

That's true only while the acetone forms a thin film; when the acetone evaporates the
water remains and beads up into slow-evaporating drops.

Not correct unless there is too much water. Acetone forms an azeotrope
with water which evaporates first, ahead of either purer water or purer
acetone. If your acetone absorbs enough water to cause this problem you
need to get your lab out of the river.


Alcohol does just as good a film-producing job, and evaporates slower
so the water is likely to evaporate simultaneously.

If you don't mind waiting, why use either?


For many materials (like those used in printed circuits) the bake-dry is required
anyhow, because the substrate isn't completely water-impermeable. The blow-off
of droplets usually is to remove dissolved dirt, not just the water and solvent.

The dirt should have been rinsed off. If you have crud remaining in the
rinse water your washer isn't working.

--

Rick C