chem 18 lecture 1 exam 3 acids and bases (1)
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8/6/2019 Chem 18 Lecture 1 Exam 3 Acids and Bases (1)
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Acids and Bases
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Brønsted-Lowry Acids and Bases
� Concept of conjugate acid-base pair
� CN-(aq) + H2O(l) HCN(aq) + OH-(aq)
� CH3COOH(aq) + H2O(l) CH3COO-(aq) + H3O+
(aq)
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Acid-Base Properties of Water
� H2O + H2O H3O+ + OH-
� for the autoionization of water:� Kw = [H3O+][OH-]
� Ion-product constant
� At 25°C, Kw = 1.0 x 10-14
� from [H3O+]=[OH-]= 1.0 x 10-7 M
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pH
� pH = -log[H3O+]
� Acidic: [H3O+] > 1.0 x 10-7, pH < 7.00
� Basic: [H3O+] < 1.0 x 10-7, pH > 7.00� Neutral: [H3O+] = 1.0 x 10-7, pH = 7.00
� pH + pOH = 14.00 (derive please)
� pH is measured by a pH meter
8/6/2019 Chem 18 Lecture 1 Exam 3 Acids and Bases (1)
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Calculate.
� How many moles of hydroxide ions is present
in a 500-mL HCl solution whose pH = 2.74?
�Calculate the pH of a NaOH solution if [OH-] =3.1 x 10-4 M
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Strength of Acids and Bases
� Strong acids/bases are strong electrolytes that
are assumed to ionize completely in water
�
HNO3(aq) + H2O H3O+
(aq) + NO3
-
(aq)
� Weak acids/bases ionize only to a limited
extent in water� NH3(aq) + H2O NH4
+(aq) + OH-
(aq)
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See animation
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Conjugate acid-base pairs properties
� 1. If an acid is strong, its conjugate base has
no measurable strength
�
2. H3O+
is the strongest acid that can exist inaqueous solution
� 3. OH- is the strongest base that can exist in
aqueous solution
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Calculate.
� What is the pH of a 0.020 M Ba(OH)2 solution?
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Ka Acid Base
Name Formula Formula Name
Large Perchloric acid HClO4 ClO4- Perchlorate ion
3.2 * 109 Hydroiodic acid HI I- Iodide
1.0 * 109
Hydrobromic acid HBr Br- Bromide1.3 * 106 Hydrochloric acid HCl Cl- Chloride
1.0 * 103 Sulfuric acid H2SO4 HSO4- Hydrogen sulfate
ion
2.4 * 101 Nitric acid HNO 3 NO3- Nitrate ion
-------- Hydronium ion H3O+ H2O Water
5.4 * 10-2 Oxalic acid HO2C2O2H HO2C2O2- Hydrogen oxalate
ion1.3 * 10-2 Sulfurous acid H2SO3 HSO3
- Hydrogen sulfite
ion
1.0 * 10-2 Hydrogen sulfate ion HSO4- SO4
2- Sulfate ion
7.1 * 10-3 Phosphoric acid H3PO4 H2PO4- Dihydrogenphospha
te ion
7.2 * 10-4 Nitrous acid HNO 2 NO3- Nitrite ion
6.6 * 10-4 Hydrofluoric acid HF F - Fluoride ion
1.8 * 10-4 Methanoic acid HCO2H HCO2- Methanoate ion
6.3 * 10-5 Benzoic acid C6H5COOH C6H5COO- Benzoate ion
5.4 * 10-5 Hydrogen oxalate
ion
HO2C2O2- O2C2O2
2- Oxalate ion
1.8 * 10-5
Ethanoic acid CH3COOH CH3COO Ethanoate (acetate)ion
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4.4 * 10-7 Carbonic acid CO32- HCO3
- Hydrogen carbonate ion
1.1 * 10-7 Hydrosulfuric acid H2S HS- Hydrogen sulfide ion
6.3 * 10-8 Dihydrogen phosphateion
H2PO4 - HPO4 2- Hydrogen phosphate ion
6.2 * 10-8 Hydrogen sulfite ion HS- S2- Sulfite ion
2.9 * 10-8 Hypochlorous acid HClO ClO- Hypochlorite ion
6.2 * 10-10 Hydrocyanic acid HCN CN- Cyanide ion
5.8 * 10-10
Ammonium ion NH4
+
NH3 Ammonia5.8 * 10-10 Boric acid H3BO3 H2BO3
- Dihydrogencarbonate
ion
4.7 * 10-11 Hydrogen carbonate ion HCO3- CO3
2- Carbonate ion
4.2 * 10-13 Hydrogen phosphate ion HPO42- PO4
3- Phosphate ion
1.8 * 10-13 Dihydrogen borate ion H2BO3- HBO3
2- Hydrogen borate ion
1.3 * 10-13 Hydrogen sulfide ion HS- S 2- Sulfide ion
1.6 * 10-14 Hydrogen borate ion HBO32- BO3
3- Borate ion
--------- water H2O Hydroxide
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Analyze.
� Predict the direction of the reaction:
� HNO2(aq) + CN-(aq) HCN(aq) + NO2
-(aq)
Will the equilibrium constant be greater than or
less than 1 in the reaction below?
CH3COOH(aq) + HCOO-(aq) CH3COO-
(aq) + HCOOH(aq)
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Ionization constants
� Ka acid
�HF(aq) H+(aq) + F-(aq)
� Ka = = 7.1 x 10-4
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Calculate.
� What is the pH of a 0.50 M HF solution?
�What is the acid ionization constant of a 0.10M HCOOH solution whose pH is 2.39?
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Percent ionization
� Measure of the extent of ionization
�=
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Base ionization constant
� NH3(aq) + H2O NH4+
(aq) + OH-(aq)
�Kb = = 1.8 x 10
-5
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Calculate.
� What is the pH of a 0.40 M NH3 solution?
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Ka,Kb,Kw
(1) CH3COOH(aq) + H2O(l) CH3COO-(aq) + H3O+
(aq) Ka
(2) CH3COO-(aq) + H2O(l) CH3COOH(aq) + OH-
(aq) Kb
(3) H2O + H2O H3O+
(aq) + OH-(aq) Kw
KaKb = Kw Ka= Kb =
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Calculate.
� What is the base ionization constant of
acetate?
�
CH3COO-
(aq) + H2O(l) CH3COOH(aq) + OH-
(aq)
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Molecular Structure and the Strength
of Acids
� 1. strength of the bond
� 2. polarity of the bond
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Hydrohalic Acids
� HF (568.2 KJ/mol)
� HCl (431.9 KJ/mol)
� HBr (366.1 KJ/mol)
� HI (298.3 KJ/mol)
� F is the most electronegative element
� BUT HF<<HCl<HBr<HI
� -due to weaker bond
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Oxoacids
� 2. Same central atom but different number of
attached O.
�
- acidity increases with increasing oxidationnumber of central atom
�
HClO4 > HClO3 > HClO2 > HClO
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Base strength
� T he weaker the conjugate acid, the stronger
the base.
Acidity: H2SO3 > CH3COOH > HCN
Basicity: HSO3-
< CH3COO-
< CN-
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Base strength
� Base strength increases with increasing
anionic charge
� N3- > O2- > F-
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Lewis Concept
� A base is a substance that can donate a pair of
electrons while an acid is a asubstance
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