On Tue, 25 Aug 2009 00:43:26 -0700, in rec.crafts.jewelry Abrasha
wrote:

Peter W. Rowe wrote:


Given the small quantity of what you need to dispose of, simply rinse it down
the drain with lots of water.

NO! NEVER ADD WATER TO SUCH A POTENT ACID SOLUTION, UNLESS YOU WANT TO
WITNESS A VIOLENT ACID EXPLOSION!

The whole situation relates to the fact that strong acids, when being diluted or
mixed with water, generate heat. A fair amount of it. A small quantity of
water mixing with a large quantity of acid can be heated to boiling, which then
spatters, a dangerous situation indeed.

But Abrasha, please re-read the situation. The amount of acid involved is
perhaps at most a teaspoon. If you run the tap water in the sink and dump that
tiny quantity of acid into it, even though this violates your normally correct
rule, the small amount of acid simply cannot heat the water (a larger quantity)
enough to cause a problem.

The rule, after all, is to add acid to water, not water to acid, right? And
running the tap and dumping the acid down the sink is doing exactly that.

Even if you did the reverse, dumping the acid in, then turning on the tap, the
added water is an instant and very large amount. With such a tiny amount of
acid, there will simply be no reaction.

It's certainly true that the rule, acid to water, not water to acid, is
something people need to know, and if it's more than a tiny amount of acid, is
important. The dangerous situation, though, usually involves something like
someone having a volume of acid and slowly pouring a thin stream of water into
it. THAT is a recipe for disaster. But a rapid addition of an overwhelmingly
larger amount of water to a small amount of acid will not be.

The key, here is the definition of "small amount". The OP in this case had one
of those tiny plastic squeeze bottles of test acid. They contain perhaps 2 ml
of acid, if that. It would be difficult to add water to it slowly enough from a
kitchen tap to cause a problem even if the acid remained in a container for the
addition. But poured down the drain at the same time as turning on the water
simply won't. I've done it many times.


I HAVE SEEN THE RESULT OF THAT. A PERMANENTLY DISFIGURED FACE OF MY
BLIND CHEMISTRY PROFESSORS AT THE UNIVERSITY OF AMSTERDAM.

The main thing to disposing of such acids is
copious dilution with water.

NO, NO, NO. NEVER EVER ADD WATER TO ACID.

Right. My sentance did not mean to indicate an order. Only the relative amount
of water to acid. Perhaps I should have been clearer. But remember, I was
commenting in the context of the OP's tiny amount of acid.


In Germany we had a standard Goldsmith's rhyme to rtemember what to do:

"Erst das Wasser, dann die Saure.
Sonst passiert das Ungeheure."

(First water, then Acid, otherwise the gruesome will happen)

In the US we are taught to remember AAA (Always Add Acid)

That done, it becomes essentially harmless. If
you had more than a tiny amount, you might want to dump it down the toilet, not
the kitchen drain, since there it's vastly diluted long before it hits any metal
plumbing (like sink strainers, etc.)

Are you out of your ****ing mind Peter?!?

No. My mind is clear. Think about it. Pouring acid into the toilet is adding
acid to water, which is correct. And again, the context of the discussion is
small amounts. I state elsewhere in the thread that the question of whether
acid should be diluted depends on the quantity. This thread discussed a very
small insignificant amount. Anything more substantial is a whole different
subject, where you'd need to consider more active neutralization of the acid in
order to prevent problems or violate pollution standards or the like.

Or, you could if you wished, neutralize
the acid first by slowly adding a solution of water and baking soda.

If you wished? This is the only way to do it. And no water of course!

It's certainly not the only way. Baking soda dissolved in water works with much
less mess. Of course, you add the acid to the baking soda solution, not the
reverse for the same reason you add acid to water, not the reverse. But there
are many other bases which would effectively neutralize an acid solution. My
preferred method the last time I needed to get rid of more than a few ml of
strong acid was a plastic bucket of crushed limestone with a bit of water in the
bottom under the crushed rock. The acid reacts to the limestone as well as with
baking soda, but without foaming up all over the place, which can make a bloody
mess. In some lab work (or acid refining, for that matter) urea (dry powder or
granules) added to HCL neutralize it effectively without any foaming or annoying
reaction, for example. (used in refining because it neutralizes excess
Hydrochloric acid without neutralizing the nitric acid componant.)


But that's
really overkill for this. Plain dilution with water is enough.

Are you nuts giving this kind of advice to a novice, who knows nothing
about these matters!

There were more complete instructions also sent in email to the OP, which
included cautions regarding amount, as well as against adding water to acid,
especially slowly.


No matter what amount, ALWAYS do it the right way. Dilute first with
baking soda, then dilute further with water.

As I said, and I know you'll argue, right depends on the situation. Keep in
mind that I've got a good deal of chem lab experience, and a family history of
professional chemists (my father). There are times when the rules need to be
blindly and mindlessly followed for safety, and beginners are often one of those
times. You are correct in this. But nothing is absolute. For example, when
I do an acid test with a drop of acid on a touchstone, I simply rinse it off
when done. That's "acid to water", against the rules. But it's not been a
problem, or produced any noticable negative effects in 30 years of doing it that
way, either for me, or anyone else I know. Would I slowly pour a bit of water
into a beaker of acid? No, of course not. That's dangerous as hell outside of
an entirely closed reaction vessel. But dumping a teaspoon of acid into the
sink with the faucet running to dilute it simply isn't the same situation, and
that situation is what we've been discussing. You can use baking soda if you
wish too. But I don't consider it necessary, and neither would the various
chemists I've known or worked with over the years, I promise you.

Peter