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Chemistry
Atomic Origins
2015-08-14
www.njctl.org
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Auto-ionization of Water
Acids and Bases
Lactic acid is one of many
metabolities produced when
we exercise. It generally loses
an H+ ion to from the lactate
ion (one of the chemicals that
causes burning sensations in
our muscles.)
In any sample of water, a small number of water molecules will
dissociate into H+ and OH- ions.
H2O(l) -------> OH-(aq) + H+(aq)
O
H
H
H
O
H
-
+
-
+
The H+ ion then typically binds to a lone pair of electrons on
another water molecule to make the hydronium ion: H3O+
2H2O(l) -------> OH-(aq) + H3O+(aq)
-
H
lactate
lactic acid
O
H
O
H
H
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Auto-ionization of Water
In 1909, a device was
invented that could
measure the H+ or H3O
+ concentration in an
aqueous solution.
H3O+(aq) = 1.0 x 10 -7 M
@ 25 C
H
O
-
H
H
O
+
H
Slide 6 / 123
1
What is the concentration of hydronium ions (H3O+)
in pure water?
A 1.0 x 10
-2
M
B 1.0 x 10 M
-5
2H2O(l) --> H3O+(aq) + OH-(aq)
Recalling our equilibrium concepts...... Kw = [H3O+][OH-]
Since equal amounts of H3O+ and OH- are created...
[H3O+] = [OH-] = 1.0 x 10 -7 M
Kw = (1.0 x 10 -7)(1.0 x 10 -7) = 1.0 x 10 -14 M
Clearly, the equilibrium lies far to the left!
Water does NOT like to dissociate.
C 1.0 x 10-7 M
D 1.0 x 10 -10 M
E 1.0 x 10-14 M
answer
Using this data, the equilibrium constant for the auto-ionization of
water can be calculated.
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Which of the following is the value of Kw for
water?
3
Which of the following would be true in pure
water?
A 1.0 x 10-2
A [H3O+] = [OH-]
B [H3O+] < [OH-]
B 1.0 x 10-4
C [OH-] = 1 x10-7 M
answer
C 1.0 x 10-7
D A and C
D 1.0 x 10-9
answer
2
E B and C
E 1.0 x 10-14
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The magnitude of K w indicates that _________
5
The molar concentration of hydronium ion,
[H O ], in pure water at 25 °C is ___________.
3
A 0
B 1
water ionizes to a very small extent
the autoionization of water is exothermic
water ionizes very quickly
water ionizes very slowly
C
E 10-14
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Calculating H3O+ or OHIn the natural world, we do not find pure water. There are always
things dissolved in it that influence the concentrations of
hydronium and hydroxide ions.
7
D 10-7
answer
A
B
C
D
+
answer
4
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Calculating H3O+ or OHLet's do some examples!
#1
What is the [OH-] in a solution with [H3O+] = 3.4 x 10-5 M?
Kw = [H3O+][OH-] rearranged to find [OH-] = Kw/[H3O+]
= 1.0 x 10-14/move
3.4 x for
10-5answer
= 2.9 x 10-10 = [OH-]
The hydronium or hydroxide concentration in a solution can be
determined easily if one knows one or the other.
Kw = [H3O+][OH-] = 1.0 x 10-14
Rearranged for [H3O+]
[H3O+] = 1.0 x 10-14/[OH-]
Rearranged for [OH-]
[OH-] = 1.0 x 10-14/[H3O+]
#2
What is the [H3O+] in a solution with [OH-] = 1.2 x 10-12
Kw = [H3O+][OH-] rearranged to find [H3O+] = Kw/[OH-]
= 1.0 x 10-14/ move
1.2 x for
10-12
= 8.3 x 10-3 = [H3O+]
answer
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Calculating H3O+ or OH-
6
Application:
Tap water is NOT pure water. There are many things dissolved in it
that affect the amount of [H3O+] and [OH-] in the water sample. Can
you think of some things that might chloride (Cl-), carbonate (CO32-)
What is the [H3O+] in an aqueous sample with an
[OH-] equal to 3.4 x 10-3 M?
be dissolved in tap water?
B 2.9 x 10-12 M
move for answer
Flouride (F-), calcium ions (Ca2+), c
C 1.0 x 10-7 M
The average concentration of H3O+ in New York City tap water is
D 9.4 x 10-7 M
5.01 x 10-8 M. What is the average [OH-]?
E 3.4 x 1011 M
answer
A 3.4 x 10-3 M
Kw = [H3O+][OH-]
rearranged to find [OH-]
= Kw/[H3O+]
move for answer
= 1.0 x 10-14/5.01x 10-8
= 1.99x 10-7 M
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7
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Which of the following would have the smallest
[OH-]?
8
The pacific ocean off the coast of Hawaii has
a [OH-] = 8.32 x 10-9 M.
A solution with [H3O+] = 2.4 x 10-1
What is the [H3O+]?
B solution with [H3O+] = 2.4 x 10-11
C solution with [H3O+] = 2.4 x 10-6
answer
E solution with [OH-] = 2.4 x 10-12
answer
D solution with [OH-] = 2.4 x 10-3
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Arrhenius Definition of Acids and Bases
Arrhenius Definition of Acids and Bases
As we have learned, when certain substances are added to
water, the H3O+ concentration changes.
In 1884, Swedish scientist
Svante Arrhenius decided to
create definitions for substances
that changed the [H3O+] in an
aqueous solution.
Furthermore, if the [H3O+] changes, it would influence the
[OH-].
Arrhenius labeled anything that increased the [H3O+] an acid
Arrhenius labeled anything that increased the [OH-] a base
Kw = [H3O+] [OH-] = 1.0x 10-14
By measuring the [H3O+] of a water solution after a substance had
been added, he could see if the substance was acidic or basic!
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Arrhenius Definition of Acids and Bases
Arrhenius Definition of Acids and Bases
By measuring the [H3O+] of a water solution after a substance had been
added, he could see if the substance was acidic or basic!
Example 1: Let's add some HCN(aq)
Example 2: Let's add some NaOH(s)
HCN(aq)
NaOH(s)
H3O+(aq) = 2.3x 10-6 M @ 25 C
H3O+(aq) = 4.1x10-11 M @ 25 C
Remember that pure water has an [H3O+] = 1.0 X 10-7M.
Since the [H3O+] is lower than 1.0 x 10-7 M thereby making the
[OH-] higher than 1.0 x 10-7M, Arrhenius would have described
NaOH as a base!
Since the [H3O+] is higher than 1.0 X 10-7M, Arrhenius would
have described HCN as an acid!
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9
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10
Which of the following solutions would be
considered by Arrhenius to be the most basic?
A 0.1 M NH3 [H3O+] = 3.4x10-10 M
A 0.1 M NaOH [H3O+] = 1x10-13 M
B 0.1 M NaOH [H3O+]= 1x10-13M
B 0.1 M HCl [OH-] =1.0 x10-13 M
C 0.1 M NaCN [OH-] = 2.6x10-4 M
D 0.1 M NH3 [H3O+] = 7.6x10-9 M
E pure water [OH-] = 1.0 x10-7 M
answer
E Pure water [H3O+]=1x10-7 M
answer
C 0.1 M HCl [H3O+] =1x10-1 M
D 0.1 M HCN [H3O+]= 2.3x10-6M
Vinegar has a [H3O+] of around 3.4 x10-3 M. Which of
the following solutions would be considered by
Arrhenius to be MORE acidic than vinegar?
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Bronsted Lowry Definition of an Acid
At this time, most scientists explained Arrhenius acids as possessing
H+ ions that could be added to water to produce [H3O+]
Arrhenius acids in action
HF(aq) + H2O(l) --> F-(aq) + H3O+(aq)
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Bronsted/Lowry Definition of Base
At this time, most scientists explained Arrhenius bases as possessing
OH- ions that would increase the [OH-] and decrease the [H3O+].
Arrhenius base in action
NaOH(aq) --> Na+(aq) + OH-(aq)
[OH-] causes [H3O+]
Here, the hydroflouric acid (HF) donates one of it's H+ ions to a water
molecule increasing the [H3O+](aq)
Two scientists - Bronsted and Lowry, working independently, decided
a more appropriate definition of an acid would be that of an H+ donor.
Unfortunately, this view required that all bases had to possess the
hydroxide ion. This was clearly not the case. Many substances, like
ammonia (NH3) or sodium phosphate (Na3PO4), were known to be
basic but did NOT have any hydroxide ions!
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Bronsted Lowry Definition of Base
Bronsted Lowry Definition of Acid and Bases
Summary
Bronsted and Lowry proposed that, insteading of possessing
hydroxide ions, a base was a substance that accepted an H+ from
water to produce OH- ions!
Acids are defined as H+ (proton) donors.
HC3H6O3(aq) + H2O(l) --> C3H6O3-(aq) + H3O+(aq)
Bronsted base in action
lactic acid
NH3(g) + H2O(l) --> NH4+(aq) + OH-(aq)
Bases are defined as H+ (proton) acceptors.
When ammonia, NH3, accepts the H+ from the water, the water
turns into OH- making the solution basic.
CN-(aq) + H2O(l) --> HCN(aq) + OH-(aq)
cyanide base
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A Bronsted acid is a substance that...
12
Which of the following could NOT act as a Bronsted
acid?
A accepts H+ ions
A HCN
B donates OH- ions
B H2 SO4
C increases the concentration of OH- ions
C NH4 +
D donates H+ ions
answer
answer
D H3 O+
E accepts OH- ions
E BF3
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A Bronsted-Lowry base is defined as a
substance that __________.
14
A increases [H ] when placed in H O
+
Which of the following compounds could never
act as a Bronsted acid?
A
SO
B
HSO
C
H SO
D
NH
E
CH COOH
4
2-
2
B decreases [H ] when placed in H O
+
4
-
2
C increases [OH ] when placed in H O
-
D
acts as a proton acceptor
E
acts as a proton donor
2
4
2
answer
13
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3
3
answer
11
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Bronsted Acids and Bases (In Depth)
Bronsted Acids and Bases (In Depth)
Acids and Bases go together
It should be noted that if an acid donates an H+, that H+ will be
accepted by another substance.
So, where there is an acid, there will be a base
Identifying an acid or a base
By examining the products and reactants of a chemical reaction,
one can identify if a substance is behaving as an acid or as a
base.
Example
HSO -(aq) + CN-(aq) --> SO (aq) + HCN(aq)
water acts an acid and donates it's H+ to become OH-
4
H
H
+
N
H
H
4
4
2-
= It's an acid!
CN-(aq) accepted an H+ to become HCN = It's a base!
H
H
2-
HSO -(aq) donated an H+ to become SO
O
N H +
H
O
-
+
H
H
4
NH3 acts as a base and accepts an H+ to become NH4+
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15
Bronsted Acids and Bases (In Depth)
Identifying an acid or a base
H O + H SO → H O + HSO
2
H O(l) + CH NH (aq) --> CH NH (aq) + H O (aq)
3
3
+
3
2
3
+
CH NH (aq) donated an H to become CH NH = It's an acid!
H2O(aq) accepted an
H+ to
move
forbecome
answerH3O+ = It's a base!
3
3
+
+
3
2
2
4
A
H SO
B
HO
C
HO
2
2
4
A
H SO
B
HO
C
HO
D
HSO
E
17
+
2
+
3
D
HSO
E
None of the above
4
-
+
4
-
None of the above
According to the following reaction, which reactant
molecule is acting as a base?
H O + HSO → H O + H SO
+
3
-
4
2
3
4
answer
2
3
-
4
A
H SO
B
HO
C
HO
D
HSO
E
2
-
2
2
4
4
2
3
answer
2
4
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According to the following reaction, which
reactant molecule is acting as a base?
H O + H SO → H O + HSO
+
4
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16
3
answer
Identify which reactant behaves as an acid and which behaves
as a base in the following reaction!
2
According to the following reaction, which
reactant molecule is acting as an acid?
+
4
-
None of the above
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For the following reaction, identify whether the
circled compound is behaving as an acid or a
base.
19
For the following reaction, identify whether the
circled compound is behaving as an acid or a
base.
H PO + H O ⇌ H PO + H O
3
2
4
A
Acid
B
2
4
-
H PO + H O ⇌ H PO + H O
+
3
3
2
4
4
-
Base
B
Base
C
Neither
C
Neither
D
Both
D
Both
E
None of the above
E
None of the above
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Bronsted Acids and Bases (In Depth)
20
Identifying an acid or a base in reversible reactions
Reactions are reversible so we must be able to identify acids and
bases based on the reverse reaction.
3
-
2
HF(aq) donates an H ion to become F (aq) = It's an acid
OH (aq) accepts an H+ to become H O(l) = It's a base
+
-
-
2
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2
A
Acid
B
Base
C
Neither
D
Both
E
None of the above
4
-
3
2
4
A
Acid
B
Base
C
Neither
D
Both
E
None of the above
-
3
+
The term conjugate comes from the Latin word “conjugare,” meaning
“to join together.”
+
answer
2
2
Conjugate Acids and Bases
H PO + H O ⇌ H PO + H O
4
4
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For the following reaction, identify whether the
circled compound is behaving as an acid or a
base.
3
For the following reaction, identify whether the
circled compound is behaving as an acid or a
base.
H PO + H O ⇌ H PO + H O
Example
F (aq) + H O(l) <--> HF(aq) + OH (aq)
-
+
3
answer
Acid
answer
A
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21
2
answer
18
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Reactions between acids and bases always yield their conjugate
bases and acids.
donates H+
HNO2(aq) + H2O(l)
Acid
Base
NO2 - (aq) +
Conjugate
base
accepts H+
H3O+(aq)
conjugate
acid
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Conjugate Acids and Bases
Conjugate Acids and Bases
To find an acid or bases conjugate in a reaction, simply write the
formula for the substance left after the H+ has been donated or
accepted.
Example: What is the conjugate acid of CO (aq)?
Since we are looking for a conjugate acid, CO must be a base
so let's have it accept an H+
CO (aq) + H --> HCO (aq)
3
3
3
2-
+
Example: What is the conjugate base of HSO (aq)?
Since we are looking for a conjugate base, HSO must be an
acid so let's have it donate an H
HSO (aq) --> SO (aq) + H (aq)
4
4
-
4
2-
-
conjugate acid
+
Dealing with charges
If you accept an H+, you become more positive
If you donate an H+, you become more negative
conjugate base
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22
-
-
+
4
3
2-
2-
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Which of the following would be the conjugate
base of HNO ?
23
Which would be the conjugate acid of HCO (aq)?
3
-
2
A NO2 B H2 NO2
C NO2
D NO
2
B HCO3
C CO3
D H CO
2-
2
E HNO2
3
answer
answer
A CO3 2-
-
E H2 CO3
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Lewis Acids and Bases
What would be the an acid/conjugate pair in the
following reaction?
NH
+ H O --> NH
+ OH
A NH2 -/H2 O
Definition
Scientists noticed that some substances could create acidic
solutions despite not having any H+ ions to donate. An example of
this was the Ca ion.
B NH2 -/NH3
G.N. Lewis proposed a mechanism for this
2
3
-
2+
Ca
2+
+
---> Ca (OH)
+
+
H
H
+
H
D H2 O/NH3
E None of these
2
O
C H2 O/OH-
-
answer
24
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The metal ion accepted a pair of electrons from the
water molecule, resulting in the donation of one of the
water's H+ ions.
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Lewis Acids and Bases
25
A Lewis acid is an electron pair acceptor. Metal ions or
molecules with incomplete octets (BF ) are good examples.
answer
A Accepts H+ ions
3
B Donates H+ ions
A Lewis base is an electron pair donor. Molecules with
unbonded electrons (NH , CN-, OH-, H O) are good examples.
3
A lewis base is a substance that...
C Accepts e- pairs
2
D Donates e- pairs
E Decreases the concentration of [OH-]
Lewis Acid
(e- pair
acceptor)
Lewis Base
(e- pair
donor)
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What are Acids and Bases?
Which of the following would likely act as a lewis
acid?
answer
26
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A NH3
B OH-
Definition Type
Acid
Base
Arrhenius (traditional)
substance that produces
H3O+ ions in aqueous
solution
substance that decreases
H3O+ ions in aqueous
solution
C CND H2O
Bronsted -Lowry
E Fe
3+
Lewis
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Class Discussion - Evolution
of a definition
Question 1: Can you think why the Arrhenius definition was
considered insuffienct?
It could not explain how a substance without hydroxide could make a
move
for answer
solution
basic
Question 2: Can you explain why Lewis felt that the Bronsted
definition was insufficient?
It required an acid to be in possession of a hydrogen atom.
move for answer
substance that donates H+ substance that accepts H+
ions in reaction
ions in reaction
substance that accepts an substance that donates an
electron pair in reaction
electron pair in reaction
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What are Acids and Bases?
The lewis definition is generally considered the most broad.
All acids are Lewis acids, most are also Bronsted acids, and
many are Arrhenius acids
Lewis
Bronsted
Arrhenius
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Amphoteric Substances
Acid and Base Strength
+
+ OH
-
donates a proton, thus acting as an acid
Because of water's amphoteric nature, it makes the perfect
solvent for most acid base reactions. Its nature allows for easier
exchange of protons between acids and bases.
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Weak acids only ionize partially
in water.
Their conjugate bases are
weak bases.
Acid strength increases
Strong
Base strength increases
Acid
100%
ionized
in H2O
Negligible
Weak
100%
protonated
in H2O
HCl
H2SO4
HNO3
H3O+
HSO4H3PO4
HF
HC2H3O2
H2CO3
H2S
H2PO4NH4+
HCO3HPO42H2O
OHH2
CH4
Strong
Negligible
Weak
Negligible
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Strong Acids
Base
Cl HSO 4NO 3H 2O
SO 42H 2PO4FC2H3O2HCO 3HS HPO 42NH 3
CO 32PO 43OH O 2HCH 3-
100%
protonated
in H2O
Substances with negligible
acidity do not ionize in water.
They will not readily give up
protons.
Their conjugate bases are
exceedingly strong.
Slide 60 / 123
27
Which of the following is NOT a strong acid?
A HBr
There are seven strong acids:
3 contain a H bound to the very
electronegative halogens:
B HF
HCl
HBr
HI
D HCl
C HI
hydrochloric acid
hydrobromic acid
hydroiodic acid
E A and C
HF, or hydrofloric acid, is a weak
acid. Although flourine is very
electronegative, the bond strength
between flourine and hydrogen is too
strong for HF to easily give up H .
+
answer
Cl HSO 4NO 3H 2O
SO 42H 2PO4FC2H3O2HCO 3HS HPO 42NH 3
CO 32PO 43OH O 2HCH 3-
Weak
Acid strength increases
Base
Negligible
HCl
H2SO4
HNO3
H3O+
HSO4H3PO4
HF
HC2H3O2
H2CO3
H2S
H2PO4NH4+
HCO3HPO42H2O
OHH2
CH4
Acid and Base Strength
Strong
Acid
Base strength increases
Slide 58 / 123
Acid and Base Strength
100%
ionized
in H2O
100%
protonated
in H2O
Base strength increases
4
Their conjugate bases are very
weak.
Weak
NH
2
Strong acids are completely
ionized in water (They all donate
their H+ ions).
Strong
3
Acid strength increases
+
Negligible
3
Weak
-
accepts a proton, thus acting as a base.
NH +H O
Above, water
Cl + H O
Cl HSO 4NO 3H 2O
SO 42H 2PO4FC2H3O2HCO 3HS HPO 42NH 3
CO 32PO 43OH O 2HCH 3-
Strong
Negligible
2
Base
HCl
H2SO4
HNO3
H3O+
HSO4H3PO4
HF
HC2H3O2
H2CO3
H2S
H2PO4NH4+
HCO3HPO42H2O
OHH2
CH4
Weak
HCl + H O
Above, water
Acid
100%
ionized
in H2O
Strong
If a substance can act both as an acid and base, it is known as
amphoteric. For example, water can act as a base or acid
depending on the situation.
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Strong Acids
Strong Acids
There are seven strong acids:
4 are from the very electron drawing
oxyanions:
The seven strong acids are:
HCl
HBr
HI
HNO nitric acid
H SO sulfuric acid
HClO chloric acid
HClO
perchloric acid
3
2
4
hydrochloric acid
hydrobromic acid
hydroiodic acid
3
4
HNO nitric acid
H SO sulfuric acid
HClO chloric acid
HClO
perchloric acid
3
Each of these anions has a central
atom that is highly electronegative
compared to hydrogen. The oxygens
that are bonded to that central atom
draw more electrons from it making it
even more electronegative and likely
to take electrons from hydrogen
forming H .
2
4
3
4
+
Slide 63 / 123
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Strong Bases
Monoprotic Acids
The seven strong acids are strong electrolytes because they
are 100% ionized. In other words, these compounds exist
totally as ions in aqueous solution.
All strong bases are group of compounds
called "metal hydroxides."
All alkali metals in Group I form hydroxides that are strong
bases: LiOH, NaOH, KOH, etc.
For the monoprotic strong acids (acids that donates only one
proton per molecule of the acid), the hydronium ion
concentration equals the acid concentration.
Only the heavier alkaline earth metals in Group II form strong
bases: Ca(OH) , Sr(OH) , and Ba(OH) .
[H O ] = [acid]
3
2
+
2
Again, these substances dissociate completely in aqueous
solution. In other words, NaOH exists entirely as Na ions and
OH ions in water.
So, if you have a solution of 0.5 M HCl, then [H O ] = 0.5 M
3
2
+
+
-
Slide 65 / 123
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Acid and Base Strength
2
3
H O is a much stronger
base than Cl , so the proton
moves from HCl to H O.
2
-
2
HCl
H2SO4
HNO3
H3O+
HSO4H3PO4
HF
HC2H3O2
H2CO3
H2S
H2PO4NH4+
HCO3HPO42H2O
OHH2
CH4
Base
Cl HSO 4NO 3H 2O
SO 42H 2PO4FC2H3O2HCO 3HS HPO 42NH 3
CO 32PO 43OH O 2HCH 3-
Base strength increases
answer
Acid strength increases
Negligible
H O(l) --> H O+ (aq) + Cl- (aq)
base
conj. acid conj. base
Weak
HCl(aq) +
acid
Acid
100%
ionized
in H2O
Strong
Negligible
In any acid-base reaction, the proton
moves toward the stronger base. In
other words, a stronger base will "hold
onto" its proton whereas a strong acid
easily releases its proton(s).
Weak
28 What would be the [H3O+] in a 0.005 M HBr solution?
100%
protonated
in H2O
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Acid and Base Strength
29 What would be the [OH-] in a 0.034 M NaOH solution?
Acetic acid is a weak acid. This means that only a small
percent of the acid will dissociate.
answer
The double headed arrow is used only in weak acid or weak
base dissociation equations since the reaction can proceed
with both the forward and reverse reactions.
CH3CO2H(aq) + H2O(l)
H3O+(aq) + CH3CO2-(aq)
A single arrow is used for strong acid or strong bases which
dissociate completely since the forward reaction is much more
favorable than the reverse reaction.
NaOH
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30
Slide 70 / 123
Strong acids have ___________ conjugate
bases.
31
A strong
B
C neutral
weak
negative
HBr, hydrobromic acid is a strong acid. This
means that _______________.
A
aqueous solutions of HBr contain equal concentrations
of H+ and OH-
B
does not dissociate at all when it is dissolved in water
C
cannot be neutralized by a base
D
dissociates completely to H+ and Br- when it dissolves in water
answer
answer
D
Na+ (aq) + OH- (aq)
Slide 71 / 123
pH
pH is defined as the negative
base-10 logarithm of the
concentration of hydronium ion.
pH = -log [H O+]
3
It is a measure of hydrogen ion
concentration, [H+ ] in a solution,
where the concentration is measured
in moles H+ per liter, or molarity.
The pH scale ranges from 0-14.
Generally when calculating pH we
round to two decimal places.
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32
Calculating pH
What is the pH of the solution with hydrogen ion concentration of
A 1.0 x 10-5
5.67x10-8 M (molar)?
B -5.00
C 5.00
pH = -log [H ]
+
D
9.00
E
-9.00
answer
First, take the log of 5.67x10-8 = -7.25
Now, change the sign from - to +
Answer: pH = 7.25
Note: If you take
the log of
-5.67x10-8 M,
you will end up
The order of operations:
1. Take the log
2. Switch the sign
with an incorrect
answer.
Slide 75 / 123
33
What is the pH of a solution with hydrogen ion
concentration of 1.0 x 10-5 M?
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What is the pH of a solution with hydrogen
ion concentration of 1.0 x 10 M?
34
-12
What is the pH of a solution whose hydronium
ion concentration is 7.14 x 10-3 M?
answer
B 12.00
answer
A 1.0 x 10-12
C 2.00
D -12.00
Slide 77 / 123
answer
36 What is the pH of a 0.34 M solution of the strong acid HI?
(Remember that strong acids ionize completely)
What is the pH of a solution whose hydronium
ion concentration is 1.92 x 10-9 M?
answer
35
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Slide 79 / 123
Slide 80 / 123
pH
pH
Application
What is the relationship between [H O+] and the pH value?
3
In order for proteins to be digested in the stomach, the pH must
be lower than 2.7. If the pH is too high, proteins will not be broken
down and may cause a food allergy or indigestion.
Below are three different [H O+]. Find the pH of each.
pH = -log [H O ]
3
3
+
A patient complains of indigestion
and a sample of stomach fluid is
taken and the [H O+] is found to
Hydrogen ion concentration, [H3O+]
in moles/Liter
be 3.4 X10-3 M. Is there a
problem with the pH?
1.0 x 10-1
pH
3
1.0 x 10-2
1.0 x 10-10
Clearly, the lower the [H3O+], the _____ the pH.
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Slide 82 / 123
basic
3
basic
low H O+
high OH-
pH
These are the
pH values for
several common
substances.
Battery acid
More acidic
pH
What is the relationship between [H3 O+], the pH value, and
the acidity and basicity of a solution?
gastric fluid
lemon juice
carbonated
beverages
vinegar
orange juice
beer
coffee
egg yolks
milk
pure rain or water
distilled water
neutral
milk of magnesia
household ammonia
low OH-
More basic
acidic
3
acidic
High H O+
household bleach
household lye
Slide 83 / 123
How Do We Measure pH?
For more accurate
measurements, one uses a
pH meter, which measures
the voltage in the solution.
blood
sea water
baking soda
Slide 84 / 123
How Do We Measure pH?
For less accurate measurements, one can use Litmus paper
“Red” paper turns blue above ~pH = 8
“Blue” paper turns red below ~pH = 5
Or an indicator (usually an organic dye)
pH range for color change
0
Methyl violet
Thymol blue
Methyl orange
Methyl red
Bromothymol blue
Phenolphthalein
Alizarin yellow R
2
4
6
8
10
12
14
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pH
[H+] < [OH-]
There are excess
hydroxide ions in
solution.
Acidic
Neutral
Basic
[H +](M)
> 1.0x10
=1.0x10
<1.0x10
-7
-7
-7
[OH-] (M)
<1.0x10
=1.0x10
> 1.0x10
-7
-7
-7
A pH = 3
B pH = 2
C pH = 11
D pH = 14
E pH = 1
pH value
<7.00
=7.00
>7.00
Slide 87 / 123
Slide 88 / 123
39
Which of the following (M) solutions would be
LEAST acidic?
A
B [H3O+] = 9.1x10-3
C [H3O+] = 1.3 x10-2
Which of the following solutions would have the
highest pH?
A [OH-] =3.4x10-3
[H3 O+] = 2.3x10-7
B [H3O+] = 5.4x10-11
C [OH-] = 3.4x10-12
answer
38
D [H3O+] =5.4x10-2
D [H3O+] = 7.8x10-9
E [OH-] =3.4x10-1
E [H3O+] = 4.5x10-4
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Slide 90 / 123
Which solution below has the highest
concentration of hydroxide ions?
41
Which solution below has the lowest
concentration of hydrogen ions?
A
pH = 3.21
A
pH = 11.40
B
pH = 7.00
B
pH = 8.53
C
pH = 8.93
C
pH = 5.91
D
pH = 12.60
D
pH =1.98
answer
40
answer
[H+] > [OH-]
There are excess
hydrogen ions in
solution.
answer
BASE
answer
ACID
Solution type
Which of the following solutions would be most
acidic?
37
Slide 91 / 123
less than
C
equal to
D
Not enough information.
answer
B
A
greater than
B
less than
C
equal to
D
Not enough information.
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Slide 94 / 123
Understanding a Log Based Scale
Which of the following would turn blue litmus paper
red?
A Solution with [OH-] = 2.3 E-7 M
Because of the base-10 logarithm, each 1.0-point value on the pH
scale differs by a value of ten.
B Solution with pH = 4
C Solution with pOH = 2
A solution with pH = 9 has a hydrogen ion concentration, [H ],
+
D A and C
that is 10 times more than a pH = 10 solution.
E B and C
answer
44
A solution with pH = 8 has a hydrogen ion concentration, [H ],
+
that is 10 or
2
100 times more than a pH = 10 solution.
Slide 95 / 123
45
answer
greater than
Slide 96 / 123
46
A solution with pH = 3 has a hydrogen ion
concentration that is __________than a
solution with pH = 5.
A solution with pH = 14 has a hydrogen ion
concentration that is __________than a
solution with pH = 11.
A
2x more
A
3x more
B
2x less
B
3x less
C
100x more
C
1000x more
D
100x less
D
1000x less
answer
A
For an acidic solution, the hydroxide ion
concentration is ______________ than the
hydrogen ion concentration.
43
For a basic solution, the hydrogen ion
concentration is ______________ than the
hydroxide ion concentration.
answer
42
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pOH
Calculating pOH
Just as the pH of a solution can be calculated by:
pH = -log[H3O+]
What is the pOH of a solution that has a [OH-] = 2.3 E-5 M?
The pOH of a solution can be calculated by:
pOH = - log[OH-]
pOH = - log[OH-]
pOH = - log(2.3 E-5)
Recall that the [OH-] and [H3O+] are inversly related so pH
and pOH are as well.
high pH
0 low
7 pH
14
low pOH
high pOH
14
7
= 4.63
0
Slide 99 / 123
47
Slide 100 / 123
pOH
What is the pOH of a solution with a
[OH-] = 2.7 x10-2 M?
Once we have calculated pOH, it is very easy to calculate
pH.
Remember that our solvent for all of our reactions is Water.
We also know that we have a Kw value for water of 1 x 10-14.
This is ALWAYS true for water. We can also determine the
following equations:
A 2.7
B 12.43
C 1.57
Kw=[H+][OH-]
answer
D -1.57
E -2.7
Throwing in our logarithms for pH, pOH and pKw we end up
with this:
pKw = pH + pOH
Remember that Kw is a constant and if we that the negative
log of that constant we get 14 so.....
14 = pH + pOH
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48
What is the pOH of a solution with a pH =5?
Therefore, if we have a pOH and we want to convert it to
pH, so long as we are using water for our solvent, we can
use the below equation to determine the pH of the solution.
A 5
14 = pH + pOH
C 7
In other words, to find the pH of a basic compound, you first
must need to determine the pOH of that compound and
then use that to determine the pH. Remember that pOH is
calculated using [OH-] and pH is calculated using [H+].
Other then that, there is no difference in the steps used to
calculate pOH and pH.
D 8
B 15
E 9
answer
pOH to pH and vice versa
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50
What is the pOH of an aqueous HCl solution with a
[H3O+] = 2.7 x10-1 M?
A 4
A 13.43
B 1 x10-4
B 0.57
C 10
C 2.7 x10-1
D 1 x10-10
D 2.7 x10+1
E 3
answer
What is the pH of an aqueous ammonia solution with
a [OH-] = 1 x 10-4 M?
answer
E 12.43
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51 What would be the pH of a 0.045 M NaOH solution?
(Recall that NaOH is a strong base and will ionize
completely)
52
Which of the following would be LEAST acidic?
A pOH = 2
B pOH = 4
answer
49
Slide 104 / 123
answer
C pH = 10
Slide 107 / 123
Calculating [H3O+] and [OH-]
from pH or pOH
D pH = 2
E pH = 11
Slide 108 / 123
Calculating [H3O+] and [OH-]
from pH or pOH
If given a pH, one can determine the [H3O+] by:
What is the [H3O+] in a lemon juice solution with a pH = 3.5?
10-pH = [H3O+]
10-3.5 = 3.2x10-4 M
If given a pOH, one can determine the [OH-] by:
What is the [H3O+] in a bottle of soda with a pOH = 11.4?
14 = pOH + pH
10-pOH = [OH-]
14 = 11.4 + pH
pH = 2.6
10-2.6 = 2.5x10-3 M
Slide 109 / 123
54
What is the OH- concentration if the pH of a solution
is 11?
A
1 x10-6
A
1 x 10-4
B
1 x10
B
1 x10-3
C
1 x10
C
1 x 10-11
D
1 x10
D
1 x1011
-8
6
12
Slide 111 / 123
answer
What is the OH- ion concentration if the pH of a
solution is 6?
answer
53
Slide 110 / 123
Slide 112 / 123
56
55 What is the hydrogen ion concentration (M) in a
solution of Milk of Magnesia whose pH = 9.8?
What is the hydronium ion concentration in a
solution whose pH = 4.29?
C 4.2 M
answer
B 9.8x10-10 M
answer
A 9.8 M
D 1.6x10-10 M
E 4.2x10-10 M
Slide 113 / 123
58
For a 1.0-M solution of a weak base, a reasonable
pH would be_____.
A
0
A
2
B
6
B
6
C
7
C
7
D
9
D
9
E
13
E
14
answer
For a 1.0-M solution of a strong acid, a
reasonable pH would be_____.
answer
57
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Buffers
Buffers
A buffer is a solution that can maintain a nearly constant pH when
diluted or when strong acids or strong bases are added to it.
A buffer solution is made up of a weak acid, HA, and its conjugate
base, A-, or a weak base and its conjugate acid.
When a strong base is added to a buffer the hydroxide OH- from the
strong base reacts with the weak acid, which gives up its H+ to form
water. The weak acid neutralizes the strong base.
http://che mcolle ctive .org/a ctivitie s /tutoria ls /buffe rs /buffe rs 3
http://che mcolle ctive .org/a ctivitie s /tutoria ls /buffe rs /buffe rs 3
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Buffers
If a strong acid is added to a buffer it will react with the weak
conjugate base to form a weak acid that does not readily dissociate,
and, therefore, does not significantly alter the pH.
Slide 118 / 123
59 Buffers are composed of
A
Strong acids to neutralize strong bases
B Strong bases to neutralize strong acids
C
A weak acid and its conjugate base
D A strong acid and its conjugate base
http://che mcolle ctive .org/a ctivitie s /tutoria ls /buffe rs /buffe rs 3
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60 A buffer solution contains carbonic acid (H2CO3)
and bicarbonate (HCO3-). When a small amount
of HCl is added to the buffer
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61 A buffer solution contains formic acid (HCO2H)
and sodium formate (HCO2Na). When a small
amount of NaOH is added to the buffer
A
+ significantly lowers the
The HCl dissociates and the H
pH of the solution.
A
- significantly raises
The NaOH dissociates and the OH
the pH of the solution.
B
The HCl dissociates and the H+ reacts with the
bicarbonate to form a neutral compound.
B
The formic acid neutralizes the hydroxide to form water.
C
The pH of the solution remains stable.
C
The sodium formate neutralizes the
hydroxide.
D
Both b and c
D
None of the above
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Buffer systems maintain a constant
pH in blood
The body maintains the pH of blood at around 7.4. If the pH level
changes just a few tenths of a pH unit, serious health consequences
can result. A decrease in blood pH is called acidosis, an increase is
called alkalosis.
There are 3 systems that regulate the pH of blood. The bicarbonate
system is the most important and is controlled by the rate of respiration.
In the bicarbonate system, carbon dioxide combines with water to form
carbonic acid, which dissociates to form bicarbonate and hydrogen ions.
CO2 + H2O
H2CO3
HCO3- + H+
Slide 123 / 123
63 How does the body's response to the condition
in the previous question help restore the pH of
the blood?
A
Breathing out reduces the amount of CO
2 present,
thereby reducing the production of carbonic acid.
B
Breathing in increases the amount of oxygen in the
blood.
C
Breathing has no effect on the pH of blood.
Slide 122 / 123
62 Based on the figure below, holding one's breath
can lead to which condition?
A
Alkalosis
B
Acidosis
C
Hemolysis