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ACIDS and BASES
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ACIDS
The word acid comes from the Latin word acidus whichmeans sour
Properties of Acids
Acids have a sour taste
Vinegar: 5% acetic acid (CH3COOH)
Citrus fruits: citric acid
Sour milk: lactic acid
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Acids cause color changes in plant dyes
Basis: Litmus paper test
Acids usually react with metals to produce hydrogen gas
2HCl (aq) + Zn (s) ZnCl2 (Aq) + H2 (g)
Acids react with carbonates and bicarbonates producingcarbon dioxide gas
HCl (aq) + NaHCO3 (aq) NaCl (aq) + H2O (l) + CO2 (g)
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Acids in aqueous solution conduct electricity: Electrolytes
Strong acids: strongly conduct electricityWeak acids: weakly conduct electricity
Acids neutralize bases
weak electrolyte strong electrolyt
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Bases
Properties of Bases
Bases have bitter taste
Bases have a slippery or soapy feel
Detergents and soaps: bases
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Bases causes color changes to plant dyes
Strong bases usually react with metals to produce hydrogen gas
2KOH (aq) + Zn (s) K2ZnO2 (aq) + H2 (g)
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Bases conduct electricity
Strong bases: strong electrolytesWeak bases: weak electrolytes
Bases neutralize acids
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THEORIES on ACIDS and BASES
Arrhenius Theory Bronsted-Lowry Trhoery Lewis Theory
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Arrhenius Theory of acids and bases
Svante Arrhenius (1859-1927)
Characterized acids and bases based on their interaction with water
Acid
Substance that
produces H+ orH3O
+ whendissolved in water
Bases
Substances thatproduce OH- whendissolved in H2O
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HCl: Arrhenius acid
HCl + H2O H3O+
(aq) + Cl-
(aq)
NH3: Arhenius base
NH3 + H2O NH4+ (aq) + OH- (aq)
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CH3COOH
CH3COOH (l) + H2O (l) CH3COO- (aq) + H3O
+ (aq)
NaOH
NaOH + H2O Na+ (aq) + OH- (aq) + H2O (l)
HX HX + H2O H3O+ (aq) + X- (aq)
B B + H2O OH-(aq)
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Why do acids and bases conduct electricity?
They conduct electricity
because they form IONSwhen in aqueousconditions
HOWEVER:
The Arrhenius concept isonly limited to solutions in
water
It fails to account acid-basereactions in the gaseous phaseor in other solvents
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Bronsted-Lowry Theory
Johannes Nicolaus Bronsted (1879-1974)Thomas Lowry (1874-1936)
Acid any substance that can donate a proton (or H+)
Base any substance that can accept a proton (H+)
Acids: proton donors
Bases: proton acceptors
Acids and bases: can be molecules or ions
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CH3COOH + H2O
CH3COO-
(aq) + H3O+
(aq)
NH3 + H2O NH4+ (aq) + OH- (aq)
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CH3COOH (aq) + NH3 (aq) CH3COO- (aq) + NH4
+ (aq)
Consider the reverse reaction
CH3COO- (aq) + NH4
+ (aq) CH3COOH (aq) + NH3 (aq)
CONJUGATE ACID/BASE PAIR
-an acid and a base related with proton transfer
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CONJUGATE ACID-BASE PAIRS
Acid-conjugate base Base-conjugate acid
CH3COOH + H2O CH3COO- (aq) + H3O
+ (aq)
Consider the reverse reaction
CH3COOH
CH3COO-
H2O
H3O+
acid1
acid2
base1
base2
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HCO3- (aq) + H2O CO3
2- (aq) + H3O+ (aq)
Identify:
HCN (aq) + H2PO42- CN- (aq) + H3PO4 (aq)
HPO42- (aq) + H2CO3 (aq) H2PO4
2- (aq) + HCO3- (aq)
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Conjugate acid base pair
Acid-conjugate base
HCl/ Cl-
CH3COOH/ CH3COO-
HBr/ Br-
Base-conjugate acid
NH3/ NH4+
HCO3- / H2CO3
H2O as an acid
H2O as a base
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What is the conjugate base pair of:
H2CO3HCO3
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HIHSO4
-
HNO3HPO4
2- What is the conjugate acid pair of:
HCO3-
SO4
2-
H2PO4-HPO4
2-
HSO3-
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Monoproticacids
HCl H+
+ Cl-
HNO3 H+ + NO3
-
CH3COOH H+ + CH3COO
-
DiproticacidsH2SO4 H
+ + HSO4-
HSO4- H+ + SO4
2-
Triproticacids
H3PO4 H+ + H2PO4
-
H2PO4- H+ + HPO4
2-
HPO42- H+ + PO4
3-
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Amphiprotic substances
Substances that can act either as an acid or a base
H2O
CH3COOH + H2O CH3COO- (aq) + H3O
+ (aq)
NH3 + H2O NH4+ (aq) + OH- (aq)
HCO3-
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Lewis Theory
Gilbert Newton Lewis (1875-1946)
Based on electron sharing rather than proton transfer
Accounts for acidic and basicsubstances that may behaves asacids and bases but do notinvolve H+
Lewis Acid a substance that accepts a pair of electrons
Lewis Base a substance that donates electrons
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CH3COOH + H2O CH3COO- (aq) + H3O
+ (aq)
NH3 + H2O NH4+ (aq) + OH- (aq)
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Lewis Acids and Bases
N H
H
H
acid base
F B
F
F
+ F B
F
F
N H
H
H
No protons donated or accepted!
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Theory Acids Bases
Arrhenius Yields H+ or H3O+
in aqueoussolutions
Yields OH- inaquoeussolutions
Bronsted-Lowry Proton (H+)donors
Protonacceptors
Lewis Electron-pairacceptors
Electron-pairdonors
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HOW ARE THE STRENGTHS OF ACIDS AND BASES MEASURED?
pH scale
Recall: H2O amphiprotic
H2O + H2O H3O+ (aq) + OH- (aq))
pH gives us an idea on how basic or acidic a substances is
pH = 7 neutralpH < 7 acidpH >7 base
pH = - log [H+]
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H2
O (l) H+ (aq) + OH- (aq)
The Ion Product of Water
Kc=[H+][OH-]
[H2O][H2O] = constant
Kc[H2O] = Kw= [H+][OH-]
The ion-product constant(Kw) is the product of the molar
concentrations of H+ and OH- ions at a particular temperature.
At 250C
Kw= [H+][OH-] = 1.0 x 10-14
[H+] = [OH-]
[H+] > [OH-]
[H+] < [OH-]
Solution Is
neutral
acidic
basic
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pH A Measure of Acidity
pH = -log [H+]
[H+] = [OH-][H+] > [OH-]
[H+] < [OH-]
Solution Is
neutralacidic
basic
[H+] = 1 x 10-7
[H+] > 1 x 10-7
[H+] < 1 x 10-7
pH = 7pH < 7
pH > 7
At 250C
pH [H+]
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pOH = -log [OH-]
[H+][OH-] = Kw= 1.0 x 10-14
-log [H+] log [OH-] = 14.00
pH + pOH = 14.00
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Calculate the pH of a 0.10 M HCl solution:
Calculate the pH of a 0.001 M HCl solution:
Calculate the pH of a 0.065 M HCl solution:
pOH?
pOH?
pOH?
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Calculate the pH of a 0.10 M NaOH solution:
Calculate the pH of a 0.008 M KOH solution:
Calculate the pH of a 1.8 x 10-6 M NaOH solution: