Ben Rotter wrote:


>
> It seems to me that there is always an anomoly between final SG and
> what you might predict anyway. ,

<Snip>

Ben,

I think I know partly why (although I haven't checked the exact
mathematics). I seem to recall from my High School Chemistry class that
water molecules and alcohol molecules fit into each other in such a way
that the total volume of the mixture is less than the volumes of the two
liquids unmixed. That is, if you add 20 ml ethanol to 80 ml water,
you'll get noticeably less than 100 ml as a result. It's a difference of
a few percent, IIRC. That means that the mixture has all of the mass of
the two liquids, but less than their additive volumes. It seems to me
that this would increase the mixture's density by about that same few
percent, maybe accounting for the difference between the predicted
density of .975 and the observed density of .990 . It's only a
difference of about 1.5% that we're talking about.

Supporting data can be seen in the chart at the end of this link,
http://www.miracosta.edu/home/dlr/210exp5.htm , but they don't quite
seem to match the exact difference, either.

It looks like this is another case of Reality thumbing its nose at our
neat predictions.

--


Mike MTM, Cokesbury, New Jersey, USA