On Jan 15, 10:39*pm, "Leon" wrote:
"Ecnerwal" wrote in message

...





In article ations,
Kevin Miller wrote:

The reason is a bit less obvious than that, as demonstrated in
high-school chemistry to make the point. At least back when I went to
high school it was - with all the skittishness about exposing young
persons to the faintest shred of real life, it's no doubt no longer in
vogue, regardless of proper safety precautions.

When you add water to acid, the water can be heated to boiling - I
forget the details of why, but I remember the effect. Effectively, you
can consider acid dilution to be an exothermic "reaction." The heat is
there in either direction, but the distribution of heat is significantly
different with acid to water .vs. water to acid. When water is added to
acid and the water flashes to steam, you get acid being flung out of the
container by the steam - not good.

Chemistry students who retained more are welcome to fill in the details,
or the web probably can as well. I don't need them, I recall the effect
and that's plenty for me.

I'll attest to that. *Brought back memories of my early automotive days and
filling dry batteries with suulfuric acid and topping off a battery with
water. *Adding water to a charged battery would result in what appeared to
be boiling acid.
Then there was the time I was filling a new battery with sulfuric acid and
the hose came off of the acid container, tghe acid poured right into my
crotch. *Thank goodness there was a Coke machine near by.

The order of mixing water and acid is very important with sulfuric
acid, but of no real concern with hydrochloric.
In the lab we keep 1+1 hydrochloric acid (1 part water + 1 part 30%
acid) on the shelf for routine use. It doesn't
fume like the concentrated stuff and is generally easier to handle.
You can spill the 1+1 on your skin and simply
rinse it off with water with no damage. It is concentrated sulfuric
acid (battery acid) that is dangerous to handle.
FWIW, the worst burn I ever got in 30 years in the lab was from
Hydrofluoric acid (the stuff used to etch glass).
Now that's some bad s---!
Paul Gilbert - retired chemist