From: Judy Seigel (jseigel@panix.com)
Date: 01/21/03-12:17:17 AM Z
On Mon, 20 Jan 2003, Joe Smigiel wrote:
>
> One thing that continues to plague me is mixing the solutions without
> forming a precipitate. I had three attempts over the weekend. All
> three had this in common - each part (a, b and c) mixed with distilled
> water. 'A' added to 'B' and mixed thoroughly. 'C' added to this
> mixture drop-by-drop. The first attempt was at room temp, not very warm
> at this time of year. As in the other two attempts, I dropped the 'C'
> solution through a syringe drop by painful drop. A bright green milky
> solution formed, the precipitate gradually settling a little. 2nd
> attempt - all solutions heated to 30 degrees centigrade - still a
> precipitate formed, but much less this time. 3rd attempt - all
> solutions at 55 degrees, mixing vessel kept in water bath to maintain
> temp. No precipitate at all, but next morning a very slight precipitate
> had settled at the bottom of the brown glass bottle. This is the
> solution I have used to coat the next batch of test paper. Do you think
> that the other solutions will be OK if I filter them?
Thinking about this later today (or actually yesterday), I wondered why
the warmer solution worked better than room temp... My knowlege of
chemistry is purely pragmatic -- but I believe a solution is warmed either
to accept more chemical than is soluble at lower temperatures or to make
something reluctant dissolve... I don't know the solubility of silver
nitrate offhand, but I do know that 20% is routine & dissolves readily.
The 4 grams to 100 cc water being only 4%, and the silver having been OK
before combination suggests some impurity in either of the others. The
one chemical I've seen consistently give trouble is FAC.
J.
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