alnovo@inwind.it
Date: 12/10/01-05:48:45 AM Z
Judy,
> You guys who know this stuff think it's more obvious than it is... that
> is, I now SURMISE what "dihydrate" means, but couldn't handily use the
> concept.
If you surmise that "dihydrate" means "with two molecules of water", you are correct.
> I think they assume in these formulas that you're using the prevalent form
> for the period, usually the monohydrate, since (I think) it keeps better.
> Anyway, in these processes, I find difference between amounts for mono and
> anhydrous are moot. Probably matters in film developers where you're
> working strictly by time & formula, but not (I find) where you're juggling
> all sorts of variables, including hand coating, and in the light, testing
> as you proceed.
There are no way, simply looking at the chemical name, to know how many water crystalization molecules have a certain substance, and there are no reasons because the "prevalent" form must be a monohydrate.
Some examples of the "common" form are: copper sulphate (5 H2O), copper chloride (2 H2O), pot. aluminium sulphate (12 H2O), iron (II) sulphate (7 H2O), sodium tetraborate (borax) (10 H2O)
The difference between anhydrous and hydrated salt can be very large; for example, pot. alum dodecahydrate contains about 50% of the anhydrous salt.
Alberto
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