1. Acids and Bases: Introductory Concepts
Arrhenius
...acids increase the ______
when dissolved in H2O.
[H+]
[OH–]
...bases increase the ______
when dissolved in H2O.
e.g., HCl and NaOH --
useful concept, but
limited to aq. solns.
Svante Arrhenius
(1859–1927)

2. Bronsted-Lowry acids: can transfer H+ to other substances (i.e., they
Johannes Bronsted
(1879–1947) :
Thomas Lowry
(1874–1936)
can transfer H+ to other
substances (i.e., they
are proton donors)
Bronsted-Lowry bases:
can accept H+ from other
substances (i.e., they
are proton acceptors)
-- H+ and H3O+ are used interchangeably
closer to reality;
“hydronium ion”
faster to write;
“hydrogen ion” H+
H3O+
-- B-L concept is NOT limited to aqueous solutions

3. NH3(aq) + H2O(l) NH4+(aq) + OH–(aq)
Arrhenius and Bronsted-Lowry definitions overlap,
in many cases.
NH3(aq) + H2O(l) NH4+(aq) + OH–(aq)
B-L base
B-L acid
Arrhenius
Bronsted
Lowry
(accepts H+)
(donates H+)
A. base
(causes [OH–] to )
One substance can’t be a Bronsted-Lowry acid unless...
another simultaneously acts as a B-L base.
-- the acid must be able to lose H+
-- the base must have a nonbonding pair
of e– that can bind with the H+ [ ] + H+
H–N–H H :
e.g., NH3 in above example

4. [ ] [ ] Amphoteric substances can be acids or bases,
depending on the reaction conditions.
HCl(aq) + H2O(l)
H3O+(aq) + Cl–(aq)
B-L base
NH3(aq) + H2O(l)
NH4+(aq) + OH–(aq)
B-L acid [ ] – [ ] +
NH3 is another example.
When a B-L acid, it morphs into NH2– on the P side.
“ “ “ base, “ “ “ NH4+ “ “ “ “ .

5. -- 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+...
and the acid has an extra H+.
HNO2(aq) + H2O(l) NO2–(aq) + H3O+(aq)
base
conj.
acid
CONJ.
BASE
ACID

6. -- Strong acids / bases easily / ____ H+.
donate
accept
-- Weak acids / bases do NOT easily / ____ H+.
donate
accept --
The stronger a/n acid / base,
the weaker its conj. base / acid.
In every acid-base rxn, the position of eq. favors the
transfer of H+ from stronger acid to stronger base.
weaker
(conjugate)
acid
weaker
(conjugate)
base
STRONGER
ACID
STRONGER
BASE

7. The Autoionization of Water
In water, we constantly
have (a little)...
H2O(l) + H2O(l) H3O+(aq) + OH–(aq)
Thus 25oC), the eq. const. for water is:
Kw = [H3O+] [OH–] = [H+] [OH–] = 1.0 x 10–14
This equation is taken to be valid for pure
water and for dilute aqueous 25oC.
[H+] > [OH–]
[H+] < [OH–]
[H+] = [OH–]
ACID
BASE
NEUTRAL

8. At 25oC, calculate the hydrogen ion concentration if
the hydroxide ion concentration is 2.7 x 10–4 M. Is
this solution an acid or a base?
[H+] [OH–] = 1.0 x 10–14
[H+] (2.7 x 10–4) = 1.0 x 10–14
[H+] = 3.7 x 10–11 M
[H+] < [OH–]
base

9. pH = –log [H3O+] = –log [H+]
The pH Scale
Definition of pH...
pH = –log [H3O+] = –log [H+] --
as [H+] / , pH /
Soren Sorensen
(1868–1939) :
0 ACID BASE 14
neutral
A change of 1 pH unit means
that [H+] (and [OH–]) has
changed by a factor of ___. 10
A solution with pH 2 is how many times more acidic
than one with pH 5?
1000X more acidic (i.e., 1000X less basic)

10. Especially in biochemical reactions, the rate law is
often dependent on the hydrogen ion concentration.
If the rate is 1st order in [H+], then doubling [H+]
would double the rate.
-- Human blood pH is
between 7.35 and 7.45.
red blood cell
white blood cell
platelet
Scanning electron microscope
micrograph of ordinary blood.

11. Blueberries grow best in soil
** Significant figures rule for logarithms:
# of sig. figs. in [ ] = # of decimal places in pH
Find the pH if the hydronium ion
concentration is 5.2 x 10–9 M.
pH = –log [H3O+]
= –log (5.2 x 10–9) =
Find the pH if the hydroxide ion
concentration is 3.9 x 10–10 M.
Blueberries grow best in soil
having a pH between 4.5 and 5.0.
[H+] [OH–] = 1.0 x 10–14
3.9 x 10–10
So [H+] = 2.56 x 10–5 M
pH = –log [H+]
= –log (2.56 x 10–5) =

12. Other equations:
pOH = –log [OH–]
[OH–] = 10–pOH
[H+] = 10–pH
pH + pOH = 14
Find [H+] if the pH = 5.22.
[H+] = 10–pH
= 10–5.22
= x 10–6 M

13. acid-base indicators: chemicals whose color depends on pH
Measuring pH
pH meter
a pair of electrodes
acid-base indicators:
chemicals whose color
depends on pH
e.g.,
litmus,
phenolphthalein,
bromthymol blue,
methyl red,
methyl orange
Bromthymol blue is
yellow at pH < 6.0
and blue at pH > 7.6.
pH paper is paper
impregnated with
mixtures of various
indicators.

14. -- these are strong electro- lytes that exist entirely as
Strong Acids and Bases
-- these are strong electro-
lytes that exist entirely as
ions in aqueous solution
-- memorize the names
and formulas of the
seven strong acids...
...and the eight strong,
hydroxide bases...
hydrochloric, HCl
hydrobromic, HBr
hydroiodic, HI
chloric, HClO3
perchloric, HClO4
nitric, HNO3
sulfuric, H2SO4
the hydroxides of...
Li, Na, K, Rb,
Cs, Ca, Sr, Ba
“strong base cations”

15. Strong electrolytes are often written using a one-sided
arrow.
e.g., HNO3(aq) H+(aq) NO3–(aq)
Find the pH of a M perchloric acid solution.
HClO4
H+ + ClO4–
init. [ ]
0.012
final [ ] ~0
0.012
0.012
(“Who cares?”)
pH = –log [H+]
= –log (0.012)
o o o o o
p p p p p =

16. If a nitric acid solution has pH = 2.66,
find the solution’s concentration.
[H+] = 10–pH
= 10–2.66
= 2.2 x 10–3 M
HNO3
H+ + NO3–
So orig. [HNO3] was
also 2.2 x 10–3 M.
Equipment for the production of nitric acid, formerly
part of a U.S. military munitions plant in Joliet, IL.

17. ** NOTE: Ca(OH)2, Sr(OH)2, and Ba(OH)2 are strong
electrolytes, but have limited solubilities.
This means that if you put a big chunk of
any of these into water, little of the chunk
will dissolve, BUT the little that does dissolve
will float around as X2+(aq) and OH–(aq),
NOT as X(OH)2(aq).
Barium hydroxide is used in the titration of weak
acids, particularly organic acids, because a clear
solution of Ba(OH)2 – unlike NaOH or KOH – will
NOT contain any carbonates; carbonates would
introduce errors into an analytical titration
because the CO32– ion acts as a weak base.

18. Find the pH of a M
solution of calcium hydroxide.
Ca(OH)2
Ca OH–
init. [ ]
0.0034
final [ ] ~0
0.0034
0.0068
(“w.c?”)
pOH = –log [OH–]
= –log (0.0068) =
pH + pOH = 14
2.17
pH = 11.83

19. Metal oxides, hydrides, and nitrides (containing O2–,
H–, and N3–, respectively) also react with water to
produce strongly basic solutions.
e.g., --
O2–(aq) + H2O(l) OH–(aq) --
H–(aq) + H2O(l) H2(g) + OH–(aq) --
N3–(aq) + 3 H2O(l) NH3(aq) + 3 OH–(aq)
OH!