Ask A Scientist© Chemistry Archive

name         robin
status       student
age          30s

Question -   How is hydrochloric acid an arrhenius and a bronsted-lowry acid?
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Hi Robin!
By 1887, Svante Arrhenius proposed definitions for acids and bases, that
somehow are still in common use today. By that definition an acid, in
aqueous solution would:
turn dye litmus from blue to red, react with active metals (as Zn, Fe or Sn)
dissolving it and producing hydrogen gas,react with certain compounds
called alkalis or bases to form water and compounds called salts.
So by that definition hydrochloric acid  (HCl in aqueous solution) is an
acid...
Arrhenius theory  has been modified through the years, as the science
progressed, but was useful for many years and still is used today for many
aqueous solutions.
But...1920 chemists were working with solvents other than water, and
experiments showed that a new theory was needed. One was suggested
in 1923,  at almost the same time by J.N.Bronsted (in Copenhagen) and
T.M. Lowry (England) that became knew as the Bronsted-Lowry theory.
By it an acid is defined  as a proton donor (an  H with a + charge), and a
base as a proton acceptor.
All the substances that Arrehenius considered acids  are also acids by
that definition. So the reaction of hydrogen chloride with water has
hydrogen chloride acting as a proton donor, so it is an acid...
And thanks for asking NEWTON!
Mabel
(Dr. Mabel Rodrigues)
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Robin-
       According to Arrhenius, and acid is a substance that produced H+
  ions in
solution. A base produces OH- ions. HCl, a strong acid (weak bonds) readily
breaks apart to for H+ and Cl- ions. That can be concluded by the great
degree of electrical conductivity of an HCl solution. An acetic acid solution
( weak acid, strong bonds) does not readily break apart in water, and has a
small fraction of the electrical conductivity that HCl does.
       A Bronsted acid is a proton donor, a base a proton acceptor.

Example-

HCl + H20 --->  H30+  + Cl-
HCl donates it proton to water. Water is converted to the theoretical
hydronium ion, H3O+. Water accepts the proton and is, therefore, the base.
Ifyou wanted more information, this is a topic found in any good high school
honors chem book or college book. Hope this helps.

Bob Blaus
York High School
Elmhurst, Illinois
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