acids and bases - springfield school...
TRANSCRIPT
Acids and Bases
Unit 10
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Properties of Acids and Bases
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Acids Bases
•Taste Sour •Taste Bitter
•Turns Litmus Dye Red •Turns Litmus Dye Blue
•Reacts with Metals to give H2 (g) •Do Not React with Metals
•Reacts with CaCO3 to give CO2 (g) •Do Not React with CaCO2
•Electrolyte •Electrolyte
•Neutralized by Bases •Neutralized by Acids
Arrhenius Definition of Acids
and Bases
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http://en.wikipedia.org/wiki/Svante_Arrhenius
Acids dissolve in water to
produce H+1 ions.
• HCl (aq) → H+(aq) + Cl – (aq)
Bases dissolve in water to
produce OH-1 ions.
•NaOH (aq) → Na+ (aq) + OH – (aq)
Arrhenius Definition of Acids
and Bases
Common Acids
Nitric Acid (HNO3)
• HNO3 (aq)→ H+(aq) + NO3
-(aq)
Sulfuric Acid (H2SO4)
• H2SO4 (aq) → 2H+ (aq)+ SO4
2-(aq)
Acetic Acid (HC2H3O2)
• HC2H3O2 (aq) → H+ (aq)+ C2H3O2
-(aq)
Common Bases
Potassium Hydroxide KOH
• KOH (s) → K + (aq) + OH - (aq)
Magnesium Hydroxide Mg(OH)2
• Mg(OH)2 (s) → Mg 2+ (aq) + 2 OH – (aq)
Calcium Hydroxide Ca(OH)2
• Ca(OH)2 (s) → Ca 2+ (aq) + 2 OH – (aq)
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Neutralization Reactions(Arrhenius Theory)
Acids and base neutralize one another to form
water and a salt. (Salt = ionic cmpd)
e.g.
HCl (aq) + NaOH (aq) → HOH (l) + NaCl (aq)
H2SO4 (aq) + 2 KOH (aq) → 2 HOH (l) + 2 KCl (aq)
2 HNO3 (aq) + Mg(OH)2 (aq) → 2 HOH (l) + 2 Mg(NO3)2 (aq)
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Naming Acids
Acids are ionic compounds. To name acids
look up the name of the anion in the acid.
a) Anion ends in ―ide‖
Acid Name = ―Hydro‖ + root of anion + ―ic‖ Acid
b) Anion ends in ―ite‖
Acid Name = Root of anion + ―ous‖ Acid
c) Anion ends in ―ate‖
Acid Name = Root of anion + ―ic‖ Acid
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Naming Acids Practice
HF . . . .
HBr . . .
HI . . . . .
H2SO3 . .
H2SO4 . .
HClO3 . .
HClO2 . .
H2CrO4 .
H2C2O4 .
HNO2 .
HNO3 . .
HCl . . .
Anion = Fluoride . . . . . . . . .
Anion = Bromide . . . . . . . . .
Anion = Iodide . . . . . . . . . .
Anion = Sulfite . . . . . . . . . .
Anion = Sulfate . . . . . . . . . .
Anion = Chlorate . . . . . . . .
Anion = Chlorite . . . . . . . . .
Anion = Chromate . . . . . . .
Anion = Oxalate . . . . . . . . .
Anion = Nitrite . . . . . . . . . .
Anion = Nitrate . . . . . . . . . .
Anion = Chloride . . . . . . . .
Hydrofluoric Acid
Hydrobromic Acid
Hydroiodic Acid
Sulfurous Acid
Sulfuric Acid
Chloric Acid
Chlorous Acid
Chromic Acid
Oxalic Acid
Nitrous Acid
Nitric Acid
Hydrochloric Acid
Acid/Base Titrations
An acid/base titration is when acid and base
are reacted with one another until they
reach the end point or equivalence point.
The end (equivalence) point occurs when
the # of moles of acid = the # of moles of
base.
The equivalence point is usually signaled
when a dye, referred to as an indicator,
changes color.
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Acid/Base Titrations
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You will titrate HCl with NaOH. You will use
a HCl solution of known concentration to
find the concentration of a the base:
HCl (aq) + NaOH (aq) → H2O (l) + NaCl (aq)
Known Volume
and Known
[HCl]
Known Volume
and Unknown
[NaOH]
Acid/Base Titrations
Use burets to deliver precise
volumes of acid and base.
Burets can measure to the nearest
0.01 mL.
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http://en.wikipedia.org/
wiki/Image:Burette.svg
Images from :
http://www.csudh.edu/oliver/demos/b
uretuse/buretuse.htm
Acid/Base Titrations
In our lab, the
equivalence
point occurs
when the
phenolphthalei
n turns from
clear to pink.
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Images from:
http://www.chemistry.w
ustl.edu/~courses/gen
chem/Labs/AcidBase/
phph.htm
Not enough
base added.
Too much
base
added.
Just
right.
Kw- A special Equilibrium Constant
Water molecules ionize to a very small
degree:
H2O (l) ↔ H+(aq) + OH-
(aq)
The equilibrium constant for the reaction is:
Keq = [H+][OH-]
This equilibrium constant is so common that
it is referred to as the dissociation constant
of water and is given the symbol, Kw.
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[H+] and [OH-] in Pure Water
The concentration of H+ and OH- in pure water
are both 1 x 10 -7 M. The Kw in pure water is:
Kw = [H+] x [OH-] = [1 x 10 -7 M] x [1 x 10 -7 M]
= 1 x 10 -14
In all aqueous solutions:
[H+][OH-] = 1 x 10 -14
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Calculations of H+ and OH- in
Aqueous SolutionsIf you know the concentration of H+ in
solution, you can always find the
concentration of OH-.
e.g. Find the [OH-] in a 0.25 M solution of HCl.
Ans: 1 x10-14 = [0.25 M][OH-] ; [OH-] = 4.0x10 -14 M
In the same way, you can find [H+] from [OH-].14
pH Scale
pH is a convenient way to express the
amount of acid or base in a solution
without having to use exponents.
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pH from [H+] [H+] from pH
pH = - log [H+] [H+] = 10 -pH
Find the pH of a 0.010 M solution
of HCl.
Find the [H+] of a solution with
pH = 3.5.
Ans: pH = -log [0.010M] = 2.00 Ans: 10 -3.5 = 0.0032 M
Examples:
pH Scale
16Image Source is http://www.ltbenvironmentalproject.com/content.aspx?id=20
[H+], [OH-], pH, and pOH
These four relationships will allow you to
solve any problems involving [H+], [OH-],
pH, and pOH:
1. [H+] x [OH-] = 1 x 10-14
2. pH + pOH = 14
3. pH = -log [H+]
4. pOH = -log [OH-]
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Brønsted Lowry Theory
The Brønsted-Lowry Theory of acids and
bases is broader than the Arrhenius
theory. According to the B-L theory:
Acids –- donate H+ ions
Bases—accept H+ ions
This theory broadens the definition of a base
beyond substances that contain the OH –
ion.
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B-L Theory of Acids and Bases
Examples of B-L Acid/Base Reactions:
HCl (aq) + OH- (aq) ↔ Cl – (aq) + HOH (aq)
NH3 (aq) + HNO3 (aq) ↔ NH4+
(aq) + NO3-
(aq)
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Acid (H+ donor)
Acid (H+ donor)
Base (H+ Acceptor)
Base (H+ Acceptor)
Conjugate Acids/Bases
According to B-L Theory, acids become
bases after they have donated an H+.
The difference between an acid and its
conjugate base is simply an H+. . .
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Acid Conjugate Base
HCl Cl -
HSO4- SO4
2-
H2SO4 HSO4-
NH4 + NH3
Strong and Weak Acids
Strong acids ionize 100% while weak acids
ionize less than 10% in water.
Strong Acid: HCl (aq) H + (aq) + Cl – (aq)
Weak Acid: HF (aq) H + (aq) + Cl – (aq)
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100%
2.5%~
Weak Acids: KAs
The strength of a weak acids can be
expressed by its equilibrium constant KA:
HA ↔ H+ + A- KA =
The larger the equilibrium constant, the
stronger the acid.
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[HA]
]][A[H
KAs of AcidsAcid Ionization Reaction KA Expression KA Value
HCl HCl ↔ H+ + Cl- Very Large
HNO3 HNO3 ↔ H+ + NO3- Very Large
H2SO4 H2SO4 ↔ 2 H+ + SO42- Large
HSO4-1 HSO4
-1 ↔ H+ + SO42- 1.3 x 10 -2
HF HF ↔ H+ + F - 6.7 x 10 -4
HC2H3O2 HC2H3O2 ↔ H+ + C2H3O2- 1.8 x 10 -5
H2S H2S ↔ H+ + HS - 1.0 x 10 -7
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[HCl]
]][Cl[H
][HNO
]][NO[H
3
3
]SO[H
]][HSO[H
42
4
][HSO
]][SO[H-
4
4
[HF]
]][F[H
][HS
]][HS[H
2
]OH[HC
]OH][C[H
232
232
Strong Vs. Concentrated
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Str
ong, C
oncentr
ate
dS
trong, D
ilute
Weak, D
ilute
Weak, C
oncentr
ate
d
Predicting Direction of Rxn
To predict the direction of a B-L acid-base
rxn, compare the KAs of the acids.
The reaction will proceed away from the
strongest acid:
HSO4- + HF ↔ H2SO4 + F –
(base) (acid) (acid) (base)
6.7 x 10 -4 Large
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Predicting Rxn Direction
Predict the direction of the following
reactions:
NO2- + H2SO3 ↔ HNO2 + HSO3
-
1.7 x 10 -2 5.1 x 10 -4
HC2H3O2 + Cl- ↔ C2H3O2- + HCl
1.8 x 10 -5 Very Large
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Acids and Bases
The End