From: Sil Horwitz (silh@earthlink.net)
Date: 08/05/00-08:39:45 PM Z
At 2000/08/05 09:59 PM -0400, Sandy wrote:
>"Alternatively, 7 g Silver(I) Oxide may be precipitated from a solution of
>10.3 g Silver Nitrate by adding a solution of 2.5 g Sodium Hydroxide; after
>filtration and washing, the moist precipitate may be dissolved in the
>Sulphamic Acid."
>
>I don't understand the concept of a chemical being "precipitated from"
>another but I have on hand a large suppy of silve nitrate and would like to
>give it a try. Can someone explain how I would do this in practice,
>especially the part about filtering and washing?
Silver oxide is insoluble in water, so when it is created from the reaction
between the silver nitrate and sodium hydroxide, it first forms a rather
gelatinous precipitate, which will settle at the bottom of the container so
much of the liquid can be decanted. The problem is that the guck at the
bottom contains both the silver oxide and sodium nitrate, so you must get
rid of the latter. So you add water to dilute the liquid, pour the mixture
into a paper filter, and then pour water several times over the stuff
collected by the filter to get rid of much of the sodium nitrate. This
crude method should remove most of the nitrate, but enough not to react
with the rest of the formula. Don't try to remove it from the filter, as
much will be imbedded in the paper fibers, but dissolve it with the
sulfamic acid in the quantity specified in the formula.
Incidentally, coffee filters should be good enough to do the job, if you
can't get standard chem lab paper filters.
One other observation: do not use "lye" as this grocery item includes many
harmful impurities. The sodium hydroxide doesn't necessarily have to be
"reagent" grade, but should as least be "purified" flakes or pellets.
"Photographic" grade is fine.
Sil Horwitz, FPSA
Technical Editor, PSA Journal
teched@psa-photo.org
silh@earthlink.net
Visit http://www.psa-photo.org/
Personal page: http://home.earthlink.net/~silh/
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