acids and bases: introductory concepts arrhenius...acids increase the ______ when dissolved in h 2...
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Acids and Bases: Introductory Concepts
Arrhenius
...acids increase the ______ when dissolved in H2O.
...bases increase the ______ when dissolved in H2O.
e.g., HCl and NaOH
--
[H+]
[OH–]
useful concept, butlimited to aq. solns.
Svante Arrhenius(1859–1927)
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Bronsted-Lowry acids:
Bronsted-Lowry bases:
-- H+ and H3O+ are used interchangeably
-- B-L concept is NOT limited to aqueous solutions
can transfer H+ to othersubstances (i.e., theyare proton donors)
can accept H+ from othersubstances (i.e., theyare proton acceptors)
closer to reality;“hydronium ion”
faster to write;“hydrogen ion” H3O+H+
Johannes Bronsted(1879–1947)
:Thomas Lowry(1874–1936)
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e.g., NH3 in above example
Arrhenius and Bronsted-Lowry definitions overlap,in many cases.NH3(aq) + H2O(l) NH4
+(aq) + OH–(aq)
One substance can’t be a Bronsted-Lowry acid unless...
-- the acid must be able to lose H+
-- the base must have a nonbonding pair of e– that can bind with the H+
A. base
B-L base
another simultaneously acts as a B-L base.
(causes [OH–] to )
(accepts H+)B-L acid(donates H+)
H–N–H
H
:H+
[ ]+
Arrhenius Bronsted Lowry
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Amphoteric substances can be acids or bases,depending on the reaction conditions.
HCl(aq) + H2O(l)
NH3(aq) + H2O(l)
H3O+(aq) + Cl–(aq)
NH4+(aq) + OH–(aq)
B-L base
B-L acid
NH3 is another example.
When a B-L acid, it morphs into NH2– on the P side.
“ “ “ base, “ “ “ NH4+ “ “ “ “ .
[ ]+
[ ]–
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and the acid has an extra H+.
-- In acid-base equilibria, protons are donated in forward and reverse reactions.
-- The two substances in a conjugate acid-base pair differ by a H+...
HNO2(aq) + H2O(l) NO2–(aq) + H3O+(aq)
ACIDCONJ.BASE
baseconj.acid
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In every acid-base rxn, the position of eq. favors thetransfer of H+ from stronger acid to stronger base.
STRONGERACID
weaker(conjugate)
acid
STRONGERBASE
weaker(conjugate)
base
-- Strong acids / bases easily / ____ H+.
-- Weak acids / bases do NOT easily / ____ H+.
donate
donate
accept
accept
-- The stronger a/n acid / base,
the weaker its conj. base / acid.