Naming Basic Acids When identifying and naming acids you are looking for two characteristics The compoundmolecule will begin with hydrogen H The number of following atoms will then determine the two ways of naming ID: 745317
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Slide1
Acids and Bases
Chapter 19Slide2
Naming Basic Acids
When identifying and naming acids, you are looking for two characteristics:
The compound/molecule will begin with hydrogen, H-
The number of following atoms will then determine the two ways of naming
A binary acid (
HCl
,
HBr
, HI, etc.) will be called
hydro-
name of the anion with an
–
ic
ending, followed by acid
Hydrochloric acid,
hydrobromic
acid,
hydroiodic
acid
An
oxyacid
is when there is a polyatomic ion for the anion such as H
2
SO
4
When this occurs, if it ends in
–
ite
then it’s a
–
ous
ending and if it ends in
–ate
then it is a
–
ic
ending.
Examples: HNO
3
– Nitric Acid; HNO
2
– Nitrous acidSlide3
Ions in Solution
How are some aqueous solutions acidic, basic or neutral?
It is based on the concentrations of H
+
and OH
-
An
acidic solution
contains more hydrogen ion than hydroxide ions
A
basic solution
contains more hydroxide ions than hydrogen ions
A
neutral solution
contains equal amount of bothSlide4
Arrhenius Acid-Base Model
This was the first model for acids and bases but was later expanded, as you will see
Arrhenius Acid:
Chemical compound that increases the [H
+
]
Arrhenius Base:
Chemical compound that increases the [OH
-
]Slide5
The Brønsted
-Lowry Model
This system was invented by two chemists, independent of one another
Acid: a hydrogen-ion donor
Base: a hydrogen-ion acceptor
acid
base
conjugate acid conjugate baseHX(aq) + H2O(l) H3O+(aq) + X-(aq)Conjugate acid is the species produced when a base accepts a hydrogen-ion and forms an acid (it can now donate the H+)Conjugate base is the species that results when an acid donates a hydrogen-ion to a base (it can now accept the H+)Slide6
Lewis Acid/Base Models
Lewis Model is designed by the same scientist, G.N. Lewis, who made the electron model (Lewis Structures)
Lewis Acid
Atom, ion or molecule that accepts an electron pair to form a covalent bond
Lewis Base
Atom, ion or molecule that donates an electron pair to form a covalent bondSlide7
Acid – Base Systems
Type
Acid
Base
Arrhenius
H
+
or H
3
O
+
producer
OH
-
producer Brønsted-LowryProton (H +) donorProton (H +) acceptor LewisElectron-pair acceptorElectron-pair donorSlide8
Water – Acid, Base, Both?
As you probably already noticed, water contains both a hydrogen-ion and a hydroxide ion (H
+
+ OH
-
)
Therefore, it can act as both an acid and/or a base in chemical reactions
As chemists, we refer to this property as
amphoteric
A substance that can act as both acids and basesSlide9
Amphoteric
1-
+
+
sulfuric acid
H
2
SO
4
water
H
2
O
hydrogen
sulfate ionHSO4-hydronium ionH3O++1
1-
+
+
sulfate ion
SO
4
2-
water
H
2
O
hydrogen
sulfate ion
HSO
4
-
hydroxide ion
OH
-
1-
2-Slide10
Multiple H+
Donators
Some acids will have only one hydrogen ion to donate
HF, HClO
4
, HNO
3
, etc.
These
are known as monoprotic acidsPolyproticAcids that can donate two hydrogen ions are known as diprotic acidsH2SO4, H2CO3 Acids that can donate three protons: triproticH3PO4Slide11
Strengths of Acids
Stronger acids will completely ionize and are good conductors of electricity
e.g.
HCl
,
HBr
, HI, HClO
4
, HNO
3, H2SO4Weak acids will not completely ionize and cannot conduct electricity as well as strong acidse.g. HF, HCN, HC2H3O2, H2S, H2CO3, HClOSo what does ionization mean?HCl(aq) + H2O(l) H3O+(aq
)
+ Cl
-
(
aq)It means that the reaction has gone to completionA weak acid would have an equilibrium symbol, not a yieldSlide12
Strengths of Bases
Similar to acids, strong bases will disassociate into their metals and hydroxide ions
Ca(OH)
2(s
)
Ca
2+
(
aq) + 2 OH-(aq)Thus ionize completely!NaOH, KOH, RbOH, CsOH, Ca(OH)2, Ba(OH)2Weak bases ionize only partially and will reach an equilibrium with their conjugate acid/base (
)
Slide13
Strengths of Conjugate
Acid-Base
Pairs
strong medium
weak very weak
Acid strength increases
HCl H
2
SO
4 HNO3 H3O+ HSO4- H3PO4 HC2H3O2 H2CO3 H2S H2PO
4
-
NH
4
+ HCO3- HPO42- H2Onegligible very weak weak medium strongBase strength increases Cl- HSO4- NO3 H2O SO42- H2PO4- C2H3O2- HCO3- HS- HPO42- NH3 CO32- PO43- OH-Slide14
pH and pOH
Concentrations of H
+
ions are often small numbers expressed in scientific notation
To simplify this, chemists use an easier way to show H
+
ion concentrations
pH scale based on common logarithms
The pH of a solution is the negative logarithm of the hydrogen ion concentration
pH = - log [H+]Thus a pH of 0.00 is a strong acid and 14.0 is a strong basepH of 7 would be neutralSlide15
pH of Common Substances
1.0
M
HCl
0
gastric
juice
1.6
vinegar
2.8
carbonated
beverage
3.0
orange
3.5apple juice3.8tomato4.2lemonjuice2.2coffee5.0bread5.5soil5.5potato5.8urine6.0milk6.4water (pure)7.0drinking water7.2
blood7.4
detergents8.0 - 9.0
bile8.0
seawater
8.5
milk of
magnesia
10.5
ammonia
11.0
bleach
12.0
1.0
M
NaOH
(lye)
14.0
8
9
10
11
12
14
13
3
4
5
6
2
1
7
0
acidic
neutral
basic
[H
+
] = [OH
-
]Slide16
Properties
electrolytes
ACIDS
BASES
turn litmus red
sour taste
react with metals to form H
2
gas
slippery feel
turn litmus blue
bitter taste
vinegar, milk, soda, apples, citrus fruits
ammonia, lye, antacid, baking soda
electrolytesSlide17
pH and pOH
Sometimes chemists find it easier to use pOH when calculating the pH of bases (or alkalinity)
pOH = - log [OH
-
]
No matter which is used they will be equal to 14.00 when added together
pH + pOH = 14.00Slide18
Calculating pH/pOH
Calculate the pH of a solution at 298 K which has a
hydronium
ion concentration of 1.0 x 10
-2
M
pH = - log [H
+
] pH = - log [1.0 x 10-2]pH = 2Now how about [H+] = 3.0 x 10-6 M ?4.0 x 10-3 M ?Slide19
Acid vs. Base
Acid
pH > 7
bitter taste
does not
react with
metals
pH < 7
sour taste
react with
metals
Alike
Different
Related toH+ (proton)concentrationpH + pOH = 14Affects pHand litmus paperBaseDifferentTopicTopicSlide20
Logarithm Math Review
Logarithm is a mathematical system based on powers of 10
This works well with scientific notation because it uses the same factor (powers of 10)
If you are given the pH (3.50), then you can use the antilog (it should be shift or second log button on the calculator) for a negative pHSlide21
Another Calculation
Recall that water is both an acid and a base
H
2
O
(l)
H
+
+ OH-Therefore, the equilibrium constant for the reaction would be Keq = [H+] [OH-] / [H2O]Since water is pure, it can be combined with Keq to equal Kw
So the new equation is
K
w
=
[H+] [OH-] Kw is always equal to 1.0 x 10-14 since there would be equal number of hydrogen and hydroxide ions (1.0 x 10-7)ProblemWhat is the hydrogen ion concentration if the hydroxide concentration is 1.0 x 10-8?Slide22
Ionic Product of Water: k
w
14 1 x 10
-14
1 x 10
-0
0
13 1 x 10
-13
1 x 10-1 1 12 1 x 10-12 1 x 10-2 2 11 1 x 10-11 1 x 10-3 3 10 1 x 10-10 1 x 10-4 4 9 1 x 10-9 1 x 10-5 5
8 1 x 10
-8
1 x 10
-6
6 6 1 x 10-6 1 x 10-8 8 5 1 x 10-5 1 x 10-9 9 4 1 x 10-4 1 x 10-10 10 3 1 x 10-3 1 x 10-11 11 2 1 x 10-2 1 x 10-12 12 1 1 x 10-1 1 x 10-13 13 0 1 x 100 1 x 10-14 14More basicMore acidicpH [H+1] [OH1-] pOH 7 1 x 10-7 1 x 10-7 7Slide23
pH Calculations
pH
pOH
[H
3
O
+
]
[OH
-]pH + pOH = 14
pH = -log[H
3
O
+
][H3O+] = 10-pHpOH = -log[OH-][OH-] = 10-pOH[H3O+] [OH-] = 1 x10-14Slide24
Acid/Base Ionization Constant
Acid Ionization Constant, term is
K
a
, and is very similar to the equilibrium constant (hence the K)
e.g. H
2
SO
4
+ H2O H3O+ + HSO4-So Ka = [H3O+] [HSO4-] / [H2SO4]+ [H2O]Base Ionization Constant, term is
K
b
, and is very similar to the equilibrium constant (hence the K)
e.g. NH
3 + H2O NH4+ + OH-So Kb = [NH4+] [OH-] / [NH3]+ [H2O]What does this all mean? Measures of strength!!Slide25
Neutralization & Titrations
Yet another sub-type chemical reaction is a
Neutralization Reaction
This involves an acid being mixed with a base
It is a double-displacement reaction!!!
With a neutralization reaction, you will always (ALWAYS!) obtain a
salt and water
Recall:
A Salt is an ionic compoundSlide26
Acid-Base Neutralization
1+
1-
+
+
Hydronium ion
Hydroxide ion
Water
H
3
O
+
OH
-
H2OWaterH2OSlide27
Neutralization & Titrations
Stoichiometry works the same with these equations but we care more about the pH or ion concentrations than the amount of substance produced
Thus, stoichiometry provides the means for
Titrations
to quantitatively measure pHSlide28
Titrations
A measured volume of an acidic or basic solution of unknown concentration is placed in a beaker. The pH is determined.
A buret (burrette) is filled with the titrating solution of known concentrations. This is the standard solution.
Measured volumes of the standard solution are added slowly and mixed into the solution in the beaker.
The pH is read and recorded after each addition.
This continues until the
equivlance point
is reached, which is the time when [H
+
] = [OH-]Slide29
Litmus PaperSlide30
pH Paper
pH 0 1 2 3 4 5 6
pH 7 8 9 10 11
12 13Slide31
Indicator
Acid color
Transition color
Base color
Litmus
Bromthymol blue
STRONG ACID – STRONG BASE
pH
2 3 4 5 6 7 8 9 10 11 12
INDICATOR COLORS IN TITRATIONSlide32
2 3 4 5 6 7 8 9 10 11 12
Indicator
Acid color
Transition color
Base color
Phenolphthalein
Phenol red
WEAK ACID – STRONG BASE
pH
INDICATOR COLORS IN TITRATIONSlide33
Phenolphthalein Indicator
Colorless = Acidic pH
Pink = Basic pHSlide34
equivalence point
14.0
12.0
10.0
8.0
6.0
4.0
2.0
0.0
0.0
10.0
20.0
30.0
40.0
pHVolume of 0.100 M NaOH added(mL)Titration of a Strong Acid With a Strong Base 0.00 1.0010.00 1.3720.00 1.9522.00 2.1924.00 2.7025.00 7.0026.00 11.3028.00 11.7530.00 11.9640.00 12.3650.00 12.52 NaOH added (mL) pHTitration Data
Solution
of NaOH
Solution
of NaOH
Solution
of HCl
H
+
H
+
H
+
H
+
Cl
-
Cl
-
Cl
-
Cl
-
Na
+
Na
+
Na
+
Na
+
OH
-
OH
-
OH
-
OH
-
25 mL
phenolphthalein - colorless
phenolphthalein - pinkSlide35
Buffered Solutions
Buffers are solutions that resist changes in pH when limited amounts of acids or bases are added
This works because the buffer solution contains a mixture of either weak acid and its conjugate base or weak base and its conjugate acid
Buffers are extremely important in both laboratory experiments and every day life
We have buffers in a our blood which maintains our slightly basic pH of ~7.4
If our pH drops .03 (acidosis) or rises .03 (alkalosis), which causes problems
Lactic acid formation is one (exercise)