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16.4 pH scale (pOH). CH. 16 ACID -- BASE. 16.1 Definition. 16.2 Bronstad-Lowry Conjugate Pairs Strength Leveling Effect. 16.3 Dissociation of water K w. 16.5 Strong Acid Strong Base pH & [ ]. 16.6 Weak Acids K a & pH % Ionization Polyprotic Acids. 16.7 Weak Bases - PowerPoint PPT Presentation
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CH. 16 ACID -- BASE 16.1Definition
16.2Bronstad-LowryConjugate PairsStrengthLeveling Effect
16.3Dissociation of waterKw
16.4pH scale (pOH)
16.5Strong AcidStrong BasepH & [ ]
16.6Weak AcidsKa & pH% IonizationPolyprotic Acids
16.7Weak BasesKb & pH Acid Base Yields
16.8Ka & Kb Relation
16.9Salt SolutionsAnions/CationsLewis
16.10Binary AcidsOxyacidsCarboxylic Acids
16.11Bronstad-Lowry
ACID BASE CHEMISTRY
TERMS, ETC.
AMPHOTERIC:Subst. acts as either an acid or a baseProton (Acidic p+): H+ ion; the acidic hydrogen(s) present in an acid
HNO3: one H+ H2SO4: two H+ H3PO4: three H+
MONOPROTIC ACID: An acid w/ one H+
DIPROTIC ACID: An acid w/ two H+
POLYPROTIC ACID: An acid w/ 3 or more H+
TERMS, ETC.
ACID: Subst. in H2O incr [H+]
BASE: Subst. in H2O incr [OH-]
HYDRONIUM ION:
H2O (l) + H+1 (aq) ---------> H3O+1 (aq)
Effects H+ Ion in H2O
BRONSTAD-LOWRY
ACID: Subst. that donate acidic proton, H+
Proton donor
BASE: Subst. that gains acidic proton, H+
Proton acceptor
HCl(g) + H2O(l) ----> H3O+(aq) + Cl-(aq)
CONJUGATE ACID-BASE PAIRS
Acid, loses H+, form conjugate baseBase, gains H+, forms conjugate acid
)(-1
42(aq)3)(-2
4)(1
4 POH NH HPO NH aqaqaq
acid1 acid2base2 base1
CONJUGATE ACID-BASE PAIRS
(aq)3)(1
4 NH NH
aq )(-1
42)(-2
4 POHHPO aqaq
Fig 16.3pg. 657
RELATIVE STRENGTH
H2O stronger base than X- X weaker base --- equilib
H2O stronger base than Cl-
+ acid ion of weak acid react w/ H2O, produces H3O+
HX(aq) + H2O(l) ----> H3O+(aq) + X-(aq)
Strong Acid + Weak Base --- Acidic
HCl(g) + H2O(l) ----> H3O+(aq) + Cl-(aq)
X- stronger base than H2O
CH3COO- stronger base than H2O
CH3COOH(aq) + H2O(l) ----> H3O+(aq) + CH3COO-(aq)
X stronger base <---- equilib
Weak Acid + Strong Base --- Basic
Proton Transfer: ability of 2 bases attract protons
AUTOIONIZATION OF WATER
Kc[H2O]2 = Kw = [H3O+][OH-] = 1.0*10-14
Solution Acid [H3O+] > [OH-]Neutral [H3O+] = [OH-] Basic [OH-] > [H3O+]
22
3c
-32
OHOHOH K
OH OH ---- OH 2 )()()(
aqaql
0 7 14
pH SCALE
STRONG ACIDIC
STRONG BASIC
MILDACIDIC
MILDBASIC
WEAK ACIDIC
WEAK BASIC
NEUTRAL ( )
Kw: constant for water, 1*10-14
pKw = -Log [H2O] = -Log [1*10-14] = -Log [10-14] -Log [1] = -(-14) - 0 = 14
Kw = [H+][OH-]1*10-14 = [H+][OH-]
pKw = pH + pOH
pH = -Log [H+] pOH = -Log [OH-]
[H+] = 1*10-pH [OH-] = 1*10-pOH
Log 1 = 0 Log 10exp = explog 106 = 6 Log 10-4 = -4
Fig. 16.5pg 663
pH -- pOH -- [H+] -- [OH-] CALCULATIONS
Formulas to Use
-w OH H K
pOH pH pK w
ConstantsKw = 1 *10 –14
pH = -log [H+]pOH = -log [OH-]
pKw = 14
Rules for LOGSLog 1 = 0
Log 10exp = exponent[H+] = 1*10-pH
[OH-] = 1*10-pOH
Rules for LOGS
Log 1 = 0
Log 10exp = exponent
Log 103.17 = 3.17
b Loga Log baLog
b Loga Log baLog
84.6 Log5.8 Log 84.65.8Log
32.4 Log12.6 Log 32.412.6Log
Calculate pH for thefollowing solutions
1) [H+] = 1 * 10-9
2) [H+] = 0.001
pH = -log (1*10-9) = -(-9) = 9
0.001 = 1*10-3
pH = -log (1*10-3) = -(-3) = 3
3) [H+] = 3.6 * 10-2
pH = -log(3.6*10-2) = 1.44
OR-log 10-2 = 2 pH = 2 – log (3.6) = 2 – 0.56 = 1.44
Find pH & pOH
pOH pKw = pH + pOH 14 = 1.44 + pOHpOH = 14 – 1.44 = 12.56
OR
HK OH- w
214
10*6.310*1
= 2.78*10-13
pOH = 13 – log 2.78 = 13 – 0.44 =
If [H+] is 6.7*10-9 mol/L, what is the pH? ACIDIC, BASIC, NEUTRALWhat is the [OH-]? What is the pOH?
pH = -log(6.7*10-9) = 9 – log 6.7 = 9 – 0.83 = 8.17 BASIC
pOH = 14 – 8.17 = 5.83
[OH-] = 1*10-5.83
Find pH Find pOH
Find [OH-]
OR
[OH-] = 1*10-14
6.7*10-9 = 1.49*10-6
TITRATIONSStrong Acid + Strong Base ------ Neutral
Strong Acid + Weak Base --- Acidic
Weak Acid + Strong Base --- Basic
Weak Acid + Weak Base ---- ???????
+/- ions of acid not react w/ H2O
+ acid ion weak acid react w/ H2O, produces H3O+
HBr + NH4OH NH4 is a weak acid reacts w/ H2O to produce H3O+
-acid ion weak base produces OH-
HCN: CN- is weak base reacts w/ H2O to produce OH-
Both +/- ions react w/ H2O
DISSOCIATIONHA: acid A-: anion Ka: acid-dissociation constant Strong Acid -- SA HA(aq) + H2O(l) --------> H3O+(aq) + A-(aq)
SA in solution; no HA present, most all H3O+
@ equilibrium Qc = Kc >>>> 1
HA
AQc
OH 3
Weak Acid -- WAHCN(aq) + H2O(l) --------> H3O+(aq) + CN-(aq)
WA in solution; no H3O+ present, most all HA@ equilibrium Qc = Kc <<<< 1
Stronger Acid ==> higher [H3O+] ===> larger Ka
Smaller Ka ==> less % dissed ====> weaker acid
STRENGTH
Strong Acid/Base ionize completely equilibrium lies far to the right HCl ------> H+ + Cl-
NaOH -----> Na+ + OH-
Weak Acid slightly ionize equilibrium lies far to the leftHC2H3O2 + H2O <-----> H+ + C2H3O2
-
]OH[HC]OHC][OH[KO]H[K
O]H][OH[HC]OHC][OH[K
232
-
2323a2eq
2232
-
2323eq
Ka: acid dissociation constantKb: base dissociation constant
IONIZATION CONSTANTS
Chlorous HClO4
Nitrous HNO2
Hydrofluoric HFFormic HCOOH
Acetic CH3COOHPropanoic CH3CH2COOH
Hypochlorous HClO
Hydrocyanic HCN
Ka Values MONOPROTIC ACIDS
Incr
eas i
ng a
cid
str e
ngth
Acid Ka
1.1*10-2
7.1*10-4
6.8*10-4
1.8*10-4
1.8*10-5
1.3*10-5
2.9*10-8
6.2*10-10
Problem Solving A-B Equilibria
Steps1. Write eqn & Ka/b expression2. I.C.E. table3. Define “x” as ; HA4. Assume “x” very small5. 5% rule
2 Assumptions1. [H3O+] from water ignore2. WA diss little, no in concen
Ka * Kb = Kw
Ka = 6.8*10-4 for 0.75 M hydrofluoric acid solution is.Determine the concentrations of H3O+, A-, & OH-. Also, find the pH, pOH, & % acid dissociation.
I 0.75 — 0 0 C -x + x + x E 0.75 - x x x
HF(aq) + H2O(l) H3O+(aq) + F-(aq)
[H3O+] = [F-]Kw = [H3O+] [OH-]
1st write eqn & Ka
2nd construct table3rd determine “change, x”
4th assume x negligible; 0.75 - x => 0.75
HFOH 3
FKa
pH = -Log(0.0223) = 1.65 pOH = 14 - 1.65 = 12.35 OR = -Log(4.4*10-13) = 12.36
% Diss = 0.0223/0.75 * 100 = 3.0 %
0.75
xx 10*8.6 4 -
3
4-
F & OH
75.010*6.8
x
13--14
10*4.4 0223.010*1 OH
HA % Dissociation
HA% = [HA]diss/[HA]init * 100The initial concen of an acid is 3.2*10-2
then at equilibrium the concen is now 6.4*10-5
What is the % diss?
HA% = [2.8*10-4]/[1.2*10-2] * 100 = 2.3 %
Classify Acid - Base Strengths
SA Halogen acids: HCl, HBr, HIOxo acids: when # O’s > 1 H+
HNO3, HClO4, H2SO4
WBCmpds w/ e--rich N atom NH3, amines
WA Halogen acid: HF H not bonded to O: HCN, H2S, H3POxo acids: when # O’s < 2 H+
HNO2, HClO2, H3PO3
Carboxylic Acids: - COOH SB
Contain O-2 or OH-
Group 1A active metals: MOH, M2O Li, Na, K, Rb, CsGroup 2A active metals: M(OH)2, MO Ca, Sr, Ba
Ka acetic acid = 1.8*10-5
Ka nitrous acid = 4.4*10-4nitrous acid more ionized in soln
BASE
NH3 + H2O <---> NH4+ +OH-
][NH]OH][NH[KO]H[K
O]H][[NH]OH][NH[K
3
-
4b2eq
23
-
4eq
Kb ammonia = 1.8*10-5
S.A.S.A. yields weak conjugate baseW.A.W.A. yields strong conj. base
MONOPROTIC ACIDSKa Acid
1.2*10-2 HSO4-
1.2*10-2 HClO2
7.2*10-4 HF
1.8*10-5 HC2H3O2
3.5*10-8 HOCl
5.6*10-10 NH4+
8.3*10-13 SO4-2
8.3*10-13 ClO2-
1.4*10-11 F-
5.56*10-10 C2H3O2-
2.9*10-7 OCl-
1.8*10-5 NH3
Kb Conj. Base
acid strength conj. base strengthHCl Strong Cl-
H2SO4 HSO4-
HNO3 NO3-
H3O+ H2O
HSO4- Weak SO4-2
H2SO3 HSO3-
H2PO4 H2PO4-
HF F-
CH3COOH CH3COO-
H2CO3 HCO3-
H2S HS-
HSO3- SO3
-2
H2PO4 HPO4-2 Weak
HCN CN-
NH4+ NH3
HCO3- CO3
-2
HPO4-2 PO4
-3
H2O OH- Strong
RXN DIRECTION Direction of SA & SB to form WA & WB
H2PO4- + NH3 <------> NH4
+ + HPO4-2
HS- + H2O <------>
H2S SA than H2O
Acid Base rxn goes dir: if HA reacts w/ base lower on list
H2PO4- SA than NH4
+
H2S + OH-
Diprotic & Triprotic Acids
H2CO3: 2 acidic protons Ka values for each H+
H CO HCO
H HCO COH2-
3
-
3
-
332 Ka1 = 4.3*10-7
Ka2 = 5.6*10-11
typically weak polyprotic acid Ka1 > Ka2 > Ka3
means???? -each step of dissociation is successively weaker-loss of 2nd & 3rd proton occurs less readily
Why???? should not be surprising think in terms of charges, +/- being attracted
Various Ways to Describe Acid Strength
Property S.A. W.A.Ka value Ka is large Ka is small
Position of dissociation equilibrium
Far to right Far to left
Equilibrium [H+] compared to [HA]o
[H+] [HA]o [H+]<<[HA]o
Strength of conj.base compared to H2O
A- much weaker base than H2O
A- much stronger base than H2O
The stronger the acid the better it is at donating H+
2 factors of Acid Strength-- depends how easily the H+ is lost1) Bond Polarity
More polarized bond, quicker H+ lost, greater acid strength2) Bond Strength
Larger “none H” atom is, weaker the bond, greater acid strength
Acid Strength Nonmetal HydridesAcid Strength Nonmetal Hydrides
Metal Ion Acid StrengthMetal Ion Acid Strength high charge density, small metal ions: Fe+3, Al+3, Cu+2, Pb+2, Zn+2, Ni+2
PROPERTIES OF SALTS pH of salt soln: A-B properties
of cation & anion1. SA + SB ----> Neutral2. SA + WB ----> Acidic3. WA + SB ---> Basic
1. Cat- & An-ions not react w/ water to form H3O+ or OH-
2. Anion inert; Cation WA, form H3O+
3. Cation inert; Anion WB, form OH-
4. WA + WB ----> ????
Both ions undergo proton transfer
Ka cation > Kb anion: ACIDICKb anion > Ka cation: BASIC
Ka cation = Kb anion: NEUTRAL
All Bronstad acids form H3O+ in water & bases OH-
SA completely form H3O+
SB completely form OH-
Lewis Acids - BasesMolecules w/ central atom < 8 val e-
Polar molecules w/ dbl bond
Metal ions dissolved in water
ID Lewis A & BCl- + BCl3 <----> BCl4
-
Cl- form coval bond to B; Cl- 4 e- pair BCl3 accepts e- pair, ACID
Leveling Effect