Intersection 9

Report
Intersection 10: Acids and Bases
11/7/06
Reading: 16.1 (p765-770) 16.3-16.7
(p773-794)
Exam 1, Problem 12 Regrade
Please turn in your exams by noon on Tuesday, 11/14
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Outline
• Equilibrium wrap up
– From last week
– Two everyday examples
– Practice questions
• Acids and Bases
–
–
–
–
–
History
Models
pH Scale
Dissociation
Identifying acids and bases
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Equilibrium
What are the characteristics of an equilibrium
reaction? Use each of the following words in a
sentence that describes an equilibrium reaction:
products and reactants
concentrations
dynamic
rates
completion
Keq
Where does the “equal” in equilibrium come from?
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Can Equilibrium be Changed?
Use LeChâtelier's Principle to predict what you will see:
Fe(NO3)3 + KSCN ↔ Fe(SCN)+2 + KNO3
red
DH < 0
M
Q trumps LeChâtelier
CaCO3(s) ↔ CaO(s) + CO2(g)
ΔH > 0
Using each method, explain what will happen to the
concentration of CO2 if solid lime (CaO) is added
to the system?
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Equilibrium is Everywhere
• Iodine thermometer
Pictures from: jchemed.chem.wisc.edu/.../
2003/Aug/abs878_1.html
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Equilibrium is Everywhere
Salting the roads
Is ice in equilibrium?
http://antoine.frostburg.edu/chem/s
enese/101/solutions/faq/why-saltmelts-ice.shtml
Picture from: www.glrc.org/story. php3?story_id=1377
What happens when salt
is added to snowy winter
roads?
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Question 1
Apatite, Ca5(PO4)3OH is the mineral in teeth.
Ca5(PO4)3OH(s)
5 Ca+2(aq) + 3PO4-4(aq) + OH-(aq)
On a chemical basis explain why drinking
milk strengthens young children's teeth.
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Problem 1
Given the following equilibrium
H2 + I2  2 HI
Keq = 25
If you have 1 mol H2, 2 mol I2 and 3 mol HI
in a 1 L flask, will you make more H2 or
HI?
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Question 2
CrO4-2(aq) + 2H+(aq) ↔ Cr2O7-2(aq) + H2O(l)
Explain what will happen to the equilibrium if
water is added to this system?
From: www.funsci.com/fun3_en/ acids/acids.htm
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Acids and Bases
What do you know about acids and bases?
What makes something acidic/basic?
Who can name the most?
2000 Top 20 Chemicals Produced in US*
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Chemical
109 kg
109 kg
1. Sulfuric acid 39.62
11. Nitric acid
7.99
2. Ethylene
25.15
12. Ammonium nitrate 7.49
3. Lime
20.12
13. urea
6.96
4. Phosphoric
acid
16.16
14. Ethyl benzene
5.91
5. Ammonia
15.03
15. Styrene
5.41
6. Propylene
14.45
16. Hydrochloric
acid
4.34
7. Chlorine
12.01
17. Ethylene oxide
3.87
8. Sodium
hydroxide
10.99
18. Cueme
3.74
9. Sodium
carbonate
10.21
19. Ammonium
sulfate
2.60
10. Ethylene
chloride
9.92
20. 1,3-butatdiene
2.01
*It does not
include minerals
which do not
require processing,
such as salt and
sulfur, and
petrochemical
feedstocks, such as
ethane and butane,
which are
considered
products of oil
companies.
http://scifun.chem.wisc.edu/chemweek/Sulf&top/Sulf&Top.html
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History of Acids and Alkalies
nefertiti.iwebland.com/ timelines/topics/drink.htm
www.catskillarchive.com/ dwellers/g.htm
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…a Brief History
The only acid know to the ancient Egyptians,
Greeks, and Romans was______? It was made by
air oxidation of fermented fruit juice (wine)
Among the alkalies known to the ancients were
potash (potassium carbonate) obtained from____,
soda (sodium carbonate) made by evaporation of
alkaline waters, and lime (calcium oxide) made by
roasting________. Caustic potash and caustic soda
(potassium and sodium hydroxides) were made by
the action of lime on soda and potash.
Kauffman, G. B. "The Bronsted-Lowry Acid-Base Concept" J. Chem Ed. 1988, 65, 2831.
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…a Brief History
Later, during the middle ages, the alchemists
learned to make aqua frotis (nitric acid),
aqua regia (a nitric-hydrochloric acid
mixture), and oil of vitriol (sulfuric acid).
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…Glauber
Mid-1600's Johann Rudolph Glauber
2 NaCl + H2SO4  2 HCl + Glauber’s salt (Na2SO4)
Acid + base = salt + water
KOH + HNO3  KNO3 + H2O
“Liquor fixus (KOH or K2CO3 solution) and spiritus acidus
nitri (HNO3) are in their nature…totally unlike, foes and
adversaries of each other…and when the two are brought
together…and the one part has overcome and killed the
other, neither a fiery liquor nor a spiritus acidus can be
found in their dead bodies, but the same has been made, as
both were before and from which they were derived
namely ordinary saltpeter (KNO3).”
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… All Acids and Alkali Theory
Otto Tachenius and Francois Sylvius tried to
simplify the chemistry of life processes by
reducing all chemical interactions within the
living organism to acid-base reactions.
What evidence can you think of to support or
discredit the theory of Tachenius and
Sylvius?
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… Boyle
Boyle (1663) noted that acids, in addition to their
sour taste, had exceptional solvent power, the
ability to color certain blue vegetable dyes red,
and a precipitating action on dissolved sulfur.
Alkalies, on the other hand, had a slippery feel and
detergent properties, the ability to dissolve oils
and sulfur, and the capacity to counteract acids
and destroy their properties. Boyle's tests showed
that some substances were neutral and did not
classify either as acids or alkalies."
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… Lemery
Nicholas Lemery (1675) described acids as having
sharp spiky atoms, which produced a pricking
sensation on the skin, and alkalies as being made
up of round particles, which made them feel
slippery or soapy.
When acids and bases were mixed, he pictured the
sharp needles of the acids as penetrating the
porous alkali globules, thus producing salts, which
were neither stinging nor slippery to the touch.
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Acids: Oxygen or Hydrogen?
Antoine Lavoisier named the gaseous element
oxygen in 1777. When sulfur or phosphorus was
burned in oxygen, the products dissolved in water
to form acids, so he concluded that oxygen was
the element common to all acid materials.
Claude Louis Berthollet (1789) showed that prussic
acid (HCN) did not contain oxygen
Humphry Davy proved Lavoisier's error more
convincingly with muriatic acid (HCl), a very
strong acid.
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Dualistic Theory
Following the development of the battery by Alessandro
Volta (1800), chemists began to use this new device to
decompose all kinds of substances. Jons Jacob
Berzelius and William Hisinger (1803) found that
when salt solutions were subjected to electrolysis,
bases were found at the negative pole and acids at the
positive pole. They interpreted this to mean that acids
and bases must carry opposite electrical charges.
Berzelius concluded that acid-base reactions were simply
the result of electrical attractions. His dualistic theory
(1812) explained all chemical interactions in terms of
neutralization of opposite electrical charges
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Arrhenius Model
(PhD describing this work received lowest possible rating from his University)
Svante August Arrhenius, during his study of electrochemistry, observed that solutions of salts, acids, and bases
were the only liquids that would conduct an electric
current. He suggested (1884) that when these compounds
dissolved in water they dissociated into charged particles,
which he called "ions."
According to the Arrhenius theory acids are compounds that
produce hydrogen ions in water solution: HCl H+ + Cland bases are substances that provide hydroxide ions in
water solution: NaOH  Na+ + OH-
A
+
H ions
HCl(aq)
in water…Hydronium?
H+ (aq) (proton) + Cl-(aq)
H2O
H3O+ (aq) (hydronium)
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Hydronium
H3O+ (H2O)6 ref 1
H3O+ (H2O)20 ref 2
H9O4 + ref 3
H5O2+ ref 4
Figures: http://itl.chem.ufl.edu/2045/lectures/lec_x.html
http://cwx.prenhall.com/petrucci/medialib/media_portfolio/17.html
1
2
3
4
Zavitsas, A.A. (2001) Properties of water solutions of electrolyes and nonelectrolytes J. Phys. Chem. B 105
7805-7815.
Hulthe, G.; Stenhagen, G.; Wennstrom, O.; Ottosson, C.H. (1997) Water cluster studied by electrospray mass
spectroscopy. J. Chromatogr. A 512 155-165.
Zundel, G.; Metzger, H. (1968) Energiebander der tunnelnden Ubershub-Protenon in flussigen Sauren. Eine
IR-spektrokpische Untersuchung der Natur der Gruppierungen H5O2+ Z. Phys. Chem. 58 225-245.
Wicke, E.; Eigen, M. Ackermann, Th. (1954) Uber den Zustand des Protons (Hydroniumions) in waBriger
Losung Z. Phys. Chem. 1 340-364.
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Acid Base Reactions
HCl (aq) + NaOH (aq)  H2O (l) + NaCl (aq)
HNO3 (aq) + KOH (aq) 
H2O (l) + KNO3 (aq)
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Bronsted-Lowry Model
Edward Franklin (1905) :
NH4Cl + NaNH2  NaCl + 2 NH3
Thomas Martin Lowry in England and
Johannes Nicholas Bronsted in Denmark
(1923) independently arrived at a more
inclusive definition of the neutralization
reaction as the transfer of a hydrogen ion
(a proton) from an acid to a base.
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Bronsted Lowry Practice
HCl (aq) + NaOH (aq)  H2O (l) + NaCl (aq)
HNO3 (aq) + KOH (aq)  H O (l) + KNO (aq)
2
3
HCl + NH3
NH4Cl
Acid: proton donor; Base: proton acceptor;
Conjugate acid; conjugate base
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Acids and Bases: Comparing
Definitions
Arrhenius
Bronsted
Acid
provider of H+ in water
Base
provider of OH- in water proton acceptor
Neutralization formation of water
proton donor
proton transfer
Equation
H+ + OH-  H2O
HA + B  BH + A
Limitations
water only
proton transfer
If baseballs were really “base”balls….
+
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Measurement of Acids and Bases
pH = -log[H3O+]
HCl + H2O → H3O+ + ClA 1.0 M solution of HCl would produce 1.0 M H3O+
pH = -log [H3O+]
= -log[ 1.0M]
=0
M
pH
[H3O+]
pH
[H3O+]
0
1M
8
1x10-8
1
0.1
9
1x10-9
2
0.01
10
1x10-10
3
0.001
11
1x10-11
4
1x10-4
12
1x10-12
5
1x10-5
13
1x10-13
6
1x10-6
14
1x10-14
7
1x10-7
How do you measure base [OH-]?
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Water undergoes an equilibrium process called autoionization.
2 H2O(l) → H3O+(aq) + OH-(aq)
• Write out the expression for the equilibrium constant (Kw)
of this reaction.
• In water, the [H3O+] and [OH-] ions are always in
equilibrium with water having an equilibrium constant
(Kw) of 1x10-14
• In pure water [H3O+] = [OH-] = 1x10-7 M. What about the
pH?
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pOH
pOH = - log[OH-]
Remember that a low pH corresponds to a high
concentration of H3O+ (acidic) solution. Therefore,
a low pOH corresponds to a high concentration of
OH- (basic) solution.
Kw =
[H3O+]*[OH-] = 1 x10-14
-log ([H3O+]*[OH-]) = - log (1 x10-14)
-log [H3O+] - log[OH-] = 14
pH + pOH = 14
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pH
[H3O+]
pOH
[OH-]
battery acid, concentrated HF
0
1M
14
1x10-14
HCl secreted by stomach lining
1
0.1
13
1x10-13
lemon juice, gastric acid, vinegar
2
0.01
12
1x10-12
grapefruit, orange juice, soda
3
0.001
11
1x10-11
tomato juice, acid rain
4
1x10-4
10
1x10-10
soft drinking water, black coffee
5
1x10-5
9
1x10-9
urine, saliva
6
1x10-6
8
1x10-8
"pure water"
7
1x10-7
7
1x10-7
sea water
8
1x10-8
6
1x10-6
baking soda
9
1x10-9
5
1x10-5
Great Salt Lake, milk of magnesia
10
1x10-10
4
1x10-4
ammonia solution
11
1x10-11
3
1x10-3
soapy water
12
1x10-12
2
1x10-2
bleaches, oven cleaner
13
1x10-13
1
1x10-1
liquid drain cleaner
14
1x10-14
0
1
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Question 3: Can you explain the
following?
Acid
pH
[H3O+]
0.1 M HCl
1.0
0.1 M
0.1 M acetic acid CH3COOH
2.9
1.26x10-3
0.1 M nitric acid HNO3
1.0
0.1 M
0.1 M nitrous acid HNO2
2.2
6.3 x10-3
0.1 M hypochlorous acid HOCl
4.2
6.3 x10-5
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Problem 2
HA(aq) + H2O(l) → A- (aq) + H3O+(aq)
What is the expression for the equilibrium
constant?
Ka = ([H3O+][A-])
[HA]
Find the Ka if a 0.1 M HNO2 measures a pH = 2.2
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Vocabulary
Strong (16 definitions):
ionizing freely in solution
Weak (10 definitions):
ionizing only slightly in solution
Favorable reaction.. Strong Reaction
goes to completion
exothermic
spontaneous
product favored
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Strong Acids Bases
An acid that dissociates completely (the equilibrium is shifted
all of the way to its conjugate base and hydronium ion) is
said to be a strong acid.
HCl(aq) + H2O(l) → H3O+(aq) + Cl-(aq)
acid
conj. base
An acid that does not dissociate completely (an equilibrium is
established in solution between the acid, its conjugate base,
and hydronium ion) is said to be a weak acid.
HClO2(aq) + H2O(l) ↔ H3O+(aq) + ClO2- (aq)
acid
conj base
Ka = ([H3O+][ClO2-]) / [HClO2]
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Strong Bases
A base that dissociates completely (the equilibrium is shifted
all of the way to its conjugate acid and hydroxide) is said
to be a strong base.
NaOH(aq) + H2O(l) → OH-(aq) + Na+(aq)
base
conj. acid
A base that does not dissociate completely (an equilibrium is
established in solution between the base, its conjugate acid,
and hydroxide) is said to be a weak base.
(CH3)3N(aq) + H2O(l) ↔ (CH3)3NH+(aq) + OH-(aq)
base
conj. acid
Kb = ([(CH3)3NH+][OH-]) / [(CH3)3N]
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Strong Acid
Weak Acid
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There are six strongly dissociating acids:
HCl
HNO3
HBr
HClO4
HI
H2SO4
There are also five bases that dissociate completely
in solution (strong):
LiOH
Ca(OH)2
NaOH
Ba(OH)2
KOH
You should commit the strong acids and bases to
memory.
Appendix F in your text book lists Ka and Kb values
for many weakly dissociating acids and bases.
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Problem 3
Trimethylamine (CH3)3N has a Kb of 6.5 x10-5.
Write out its chemical reaction with water:
What is the [OH-] of a 0.010 M solution of
triethylamine?
What is the pOH?
What is the pH?
M
What kinds of hydrogen atoms
(protons) are acidic?
H-halogen (HF, HCl, HBr, HI)
H2O
H2S (Ka1 = 8.9x10-8)
Oxoacids (H-polyatomic ions) (H2CO3, HNO3, etc.)
HCN
O
H
OH
O
C
C
HO
C
H
C
OH
OH
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Organic Acids
O
O
+ H2O
R
C
OH
+
R
C
O-
RCOOH
O-
R
C
O
H3O
+
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Bases
O
OH
R3N
H 2N
CH
C
OH
CH2
O
CH2
O
C
H2N
CH
C
OH
C
O
OH
HN
CH3
OH
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Collecting Samples
Obtain Whirl pack bags
How do you fill the bags?
How many samples should you take?
How to store samples?
Filter (acid wash all glassware)
You may need special sampling techniques!
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Blanks
• Field blank
– Controls for contamination during travel
• Lab Blank
– Controls for contamination during analysis

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