Ask A Scientist© Chemistry Archive

 >    name         Steve
 >    status       student
 >    age          16

 >    Question -   (I'm not sure if this qualifies as a good question so I
 > apologize if I am wasting your time): I was wondering if you could please
 > explain to me the difference between hydrochloride, hydrogen chloride,
 > and hydrochloric acid? Thank you very much for your time.

You are right in thinking that these all have something to do with each
other.  Hydrogten chloride is the molecule HCl.  This is also known as
hydrochloric acid, especially when it is dissolved in water.  (When
dissolved in water, it dissociates to H+ and Cl-, both surrounded by water
molecules.)  "Hydrochloride" is the name given to salts of bases, usually
amines, with hydrochloric acid.  For example, an amine like strychnine can
react with hydrochloric acid to protonate a nitrogen atom in the strychnine,
making a positively-charged conjugate acid.  The chloride hangs around to
provide charge balance.

Dr. Barrans

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Dear Steve,
good question.

Hydrogen chloride and hydrochloric acid are the same compound, HCl.
Some people call HCl (aq) hydrochloric acid and
HCl (g or l) hydrogen chloride;
in fact I would go so far as to call this a widespread practice.
This is to highlight the fact that HCl(aq) is not a molecule in
solution, but is really H+ (aq) + Cl- (aq).

IUPAC says we should call HCl hydrogen chloride no matter what its
state, so no one can say you're wrong if you do too. But the dictionary
is not always in step with the language people are actually using...

Hydrochloride is an obsolete name for hydrogen chloride and is
no longer widely used. I can't find it in any modern college-
level chemistry textbook.

Finally, an ancient name for HCl is "muriatic acid," just for
your information...this name is still used in the construction
industry.

best regards,
prof. topper
dept of chemistry
the cooper union
new york, ny
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