1 CH4. Acids and Bases. 2 Bronsted-Lowry Bronsted-Lowry definitions: Acid = proton donor; Base =...
-
Upload
tracy-daniel -
Category
Documents
-
view
235 -
download
2
Transcript of 1 CH4. Acids and Bases. 2 Bronsted-Lowry Bronsted-Lowry definitions: Acid = proton donor; Base =...
![Page 1: 1 CH4. Acids and Bases. 2 Bronsted-Lowry Bronsted-Lowry definitions: Acid = proton donor; Base = proton acceptor HF (aq) + H 2 O H 3 O + (aq) + F - (aq)](https://reader036.fdocuments.us/reader036/viewer/2022081504/56649f505503460f94c73018/html5/thumbnails/1.jpg)
1
CH4. Acids and Bases
![Page 2: 1 CH4. Acids and Bases. 2 Bronsted-Lowry Bronsted-Lowry definitions: Acid = proton donor; Base = proton acceptor HF (aq) + H 2 O H 3 O + (aq) + F - (aq)](https://reader036.fdocuments.us/reader036/viewer/2022081504/56649f505503460f94c73018/html5/thumbnails/2.jpg)
2
Bronsted-Lowry
Bronsted-Lowry definitions:
Acid = proton donor; Base = proton acceptor
HF (aq) + H2O H3O+ (aq) + F- (aq)BL acid BL base
Fluoride ion is the conjugate base of HF
Hydronium ion is the conjugate acid of H2O
![Page 3: 1 CH4. Acids and Bases. 2 Bronsted-Lowry Bronsted-Lowry definitions: Acid = proton donor; Base = proton acceptor HF (aq) + H 2 O H 3 O + (aq) + F - (aq)](https://reader036.fdocuments.us/reader036/viewer/2022081504/56649f505503460f94c73018/html5/thumbnails/3.jpg)
3
Amphiprotic species
Amphiprotic – species that can act as BL acid or base
NH3 (aq) + H2O NH4+ (aqu) + OH (aqu)
BL acid hydroxide
Kb = base dissociation constant = [NH4+] [OH] / [NH3]
H2O is amphiprotic - it’s a base with HF, but an acid with NH3
BL base
![Page 4: 1 CH4. Acids and Bases. 2 Bronsted-Lowry Bronsted-Lowry definitions: Acid = proton donor; Base = proton acceptor HF (aq) + H 2 O H 3 O + (aq) + F - (aq)](https://reader036.fdocuments.us/reader036/viewer/2022081504/56649f505503460f94c73018/html5/thumbnails/4.jpg)
4
BL acid/base strength
Ka, the acidity constant, measures acid strength as:
Ka = [H3O+] [A-] / [HA]
pKa = - log Ka
When pH = pKa, then [HA] = [A-]
For strong acids
pKa < 0
pKa(HCl) ≈ -7
![Page 5: 1 CH4. Acids and Bases. 2 Bronsted-Lowry Bronsted-Lowry definitions: Acid = proton donor; Base = proton acceptor HF (aq) + H 2 O H 3 O + (aq) + F - (aq)](https://reader036.fdocuments.us/reader036/viewer/2022081504/56649f505503460f94c73018/html5/thumbnails/5.jpg)
5
BL acid/base strengths
![Page 6: 1 CH4. Acids and Bases. 2 Bronsted-Lowry Bronsted-Lowry definitions: Acid = proton donor; Base = proton acceptor HF (aq) + H 2 O H 3 O + (aq) + F - (aq)](https://reader036.fdocuments.us/reader036/viewer/2022081504/56649f505503460f94c73018/html5/thumbnails/6.jpg)
6
Kw
Kw = water autodissociation (autoionization) constant
2 H2O H3O+ (aqu) + OH- (aqu)
Kw = [H3O+] [OH-] = 1 x 10-14 (at 25°C)
Using the above, you should prove that for any conjugateacid-base pair:
pKa + pKb = pKw = 14
![Page 7: 1 CH4. Acids and Bases. 2 Bronsted-Lowry Bronsted-Lowry definitions: Acid = proton donor; Base = proton acceptor HF (aq) + H 2 O H 3 O + (aq) + F - (aq)](https://reader036.fdocuments.us/reader036/viewer/2022081504/56649f505503460f94c73018/html5/thumbnails/7.jpg)
7
Polyprotic acids
H3PO4 + H2O H2PO4- + H3O+ pKa1 = 2.1
H2PO4- + H2O HPO4
2- + H3O+ pKa1 = 7.4
HPO42- + H2O PO4
3- + H3O+ pKa1 = 12.7
Since pKa values are generally well-separated, only 1 or 2 species will be present at significant concentration at any pH
![Page 8: 1 CH4. Acids and Bases. 2 Bronsted-Lowry Bronsted-Lowry definitions: Acid = proton donor; Base = proton acceptor HF (aq) + H 2 O H 3 O + (aq) + F - (aq)](https://reader036.fdocuments.us/reader036/viewer/2022081504/56649f505503460f94c73018/html5/thumbnails/8.jpg)
8
Solvent levelingThe strongest acid possible in aqueous solution is H3O+
Ex: HCl + H2O H3O+ (aq) + Cl- (aq)
there is no appreciable equilibrium, this reaction goes quantitatively; the acid form of HCl does not exist in aqueous solution
Ex: KNH2 + H2O K+ (aq) + OH- (aq) + NH3 (aq)
this is solvent leveling, the stable acid and base species are the BL acid-base pair of the solvent
NH2- = imide anion
NR2- , some substituted
imide ions are less basic and can exist in aq soln
![Page 9: 1 CH4. Acids and Bases. 2 Bronsted-Lowry Bronsted-Lowry definitions: Acid = proton donor; Base = proton acceptor HF (aq) + H 2 O H 3 O + (aq) + F - (aq)](https://reader036.fdocuments.us/reader036/viewer/2022081504/56649f505503460f94c73018/html5/thumbnails/9.jpg)
9
Solvent leveling
Only species with 0 < pKa < 14 can exist in aqueous solutions.
The acid/base range for water stability pKw, i.e. 14 orders of mag in [H+].
Other solvents have different windows and different leveling effects.
![Page 10: 1 CH4. Acids and Bases. 2 Bronsted-Lowry Bronsted-Lowry definitions: Acid = proton donor; Base = proton acceptor HF (aq) + H 2 O H 3 O + (aq) + F - (aq)](https://reader036.fdocuments.us/reader036/viewer/2022081504/56649f505503460f94c73018/html5/thumbnails/10.jpg)
10
Solvent leveling2EtOH EtOH2
+(solv) + EtO (solv) K ~ 1020
chemistry in the range of -3 < pKa < 17
NH3 NH4+(solv) + NH2
(solv)
ammonium imide
chemistry in the range of 10 < pKa < 38
Na (m) Na+ (solv) + NH2(solv) + ½ H2 (g)
Na+ (solv) + e (solv)
NH3(l)
slowvery strong base
OH
O2
![Page 11: 1 CH4. Acids and Bases. 2 Bronsted-Lowry Bronsted-Lowry definitions: Acid = proton donor; Base = proton acceptor HF (aq) + H 2 O H 3 O + (aq) + F - (aq)](https://reader036.fdocuments.us/reader036/viewer/2022081504/56649f505503460f94c73018/html5/thumbnails/11.jpg)
11
Acid/base chemistry of complexes
Aqueous chemistry:
Fe(NO3)3 [Fe(OH2)6]3+(aq) + 3 NO3(aq)
2 [Fe(OH2)6]3+ (aq) [Fe2(OH2)10OH]5+ (aq) + H3O+(aq)
Hexaaquairon(III), pKa ~ 3
H2O
dimer
![Page 12: 1 CH4. Acids and Bases. 2 Bronsted-Lowry Bronsted-Lowry definitions: Acid = proton donor; Base = proton acceptor HF (aq) + H 2 O H 3 O + (aq) + F - (aq)](https://reader036.fdocuments.us/reader036/viewer/2022081504/56649f505503460f94c73018/html5/thumbnails/12.jpg)
12
Aqua, hydroxo, oxoacids
aqua acid M(OH2)xn+ ex: [Cu(OH2)6]2+ hexaaquacopper(II) cation
hydroxoacid M(OH)x ex: B(OH)3 , Si(OH)4 pKa ~ 10
oxoacid MOp(OH)q p and q designate oxo and hydroxo
ligands
ex: H2CO3 (aq) + H2O HCO3 (aq) + H3O+
(aq)
carbonic acid bicarbonate
pKa ~ 3.6
CO2 (g) + H2O
![Page 13: 1 CH4. Acids and Bases. 2 Bronsted-Lowry Bronsted-Lowry definitions: Acid = proton donor; Base = proton acceptor HF (aq) + H 2 O H 3 O + (aq) + F - (aq)](https://reader036.fdocuments.us/reader036/viewer/2022081504/56649f505503460f94c73018/html5/thumbnails/13.jpg)
13
Trends in acidityFor aqueous ions:
1. Higher charge is more acidic
pKa of [Fe(OH2)]3+ ~ 3
pKa of [Fe(OH2)]62+ ~ 9
2. Smaller radius is more acidic
Mn2+ Cu2+
early TM late TM
lower Z* higher Z*
=> larger radius => smaller radius
less acidic more acidic
pKa vs z2 / (r++ d)
Na+ (aqu) = [Na(OH2)6]+ has pKa > 14 so it’s a spectator ion in aqu soln
![Page 14: 1 CH4. Acids and Bases. 2 Bronsted-Lowry Bronsted-Lowry definitions: Acid = proton donor; Base = proton acceptor HF (aq) + H 2 O H 3 O + (aq) + F - (aq)](https://reader036.fdocuments.us/reader036/viewer/2022081504/56649f505503460f94c73018/html5/thumbnails/14.jpg)
14
AnhydridesEx: H2O + SO3 H2SO4
anhydride acid form
Acidic
SO3 / H2SO4
“P2O5” / H3PO4
CO2/H2CO3
Basic
Na2O / NaOH
Amphoteric
Al2O3 / Al(OH)3
![Page 15: 1 CH4. Acids and Bases. 2 Bronsted-Lowry Bronsted-Lowry definitions: Acid = proton donor; Base = proton acceptor HF (aq) + H 2 O H 3 O + (aq) + F - (aq)](https://reader036.fdocuments.us/reader036/viewer/2022081504/56649f505503460f94c73018/html5/thumbnails/15.jpg)
15
Trends in acidity
![Page 16: 1 CH4. Acids and Bases. 2 Bronsted-Lowry Bronsted-Lowry definitions: Acid = proton donor; Base = proton acceptor HF (aq) + H 2 O H 3 O + (aq) + F - (aq)](https://reader036.fdocuments.us/reader036/viewer/2022081504/56649f505503460f94c73018/html5/thumbnails/16.jpg)
16
Common acidsHNO3 NO3
(D3h)
Nitric acid Nitrate
HNO2 NO2 (C2v)
Nitrous acid Nitrite
H3PO4 PO43 (Td)
Phosphoric acid Phosphate
H3PO3 HPO32 (C3v)
Phosphorous acid Phosphite
You should know these!
![Page 17: 1 CH4. Acids and Bases. 2 Bronsted-Lowry Bronsted-Lowry definitions: Acid = proton donor; Base = proton acceptor HF (aq) + H 2 O H 3 O + (aq) + F - (aq)](https://reader036.fdocuments.us/reader036/viewer/2022081504/56649f505503460f94c73018/html5/thumbnails/17.jpg)
Common acids
17
H2SO4 SO42 (Td)
Sulfuric acidSulfate
H2SO3 SO32 (C3v)
Sulfurous acidSulfite
You should know these!
![Page 18: 1 CH4. Acids and Bases. 2 Bronsted-Lowry Bronsted-Lowry definitions: Acid = proton donor; Base = proton acceptor HF (aq) + H 2 O H 3 O + (aq) + F - (aq)](https://reader036.fdocuments.us/reader036/viewer/2022081504/56649f505503460f94c73018/html5/thumbnails/18.jpg)
Common acids
18
HClO4 ClO4 (Td)
Perchloric acid Perchlorate
HClO3 ClO3 (C3v)
Chloric acid Chlorate
HClO2 ClO2 (C2v)
Chlorous acid Chlorite
HOCl OCl
Hypochlorous acid Hypochlorite
You should know these!
![Page 19: 1 CH4. Acids and Bases. 2 Bronsted-Lowry Bronsted-Lowry definitions: Acid = proton donor; Base = proton acceptor HF (aq) + H 2 O H 3 O + (aq) + F - (aq)](https://reader036.fdocuments.us/reader036/viewer/2022081504/56649f505503460f94c73018/html5/thumbnails/19.jpg)
19
Pauling’s rules for pKa‘s of oxoacids
1. Write formula as MOp(OH)q
2. pKa 8 – 5p
3. Each succeeding deprotonation increases the pKa by 5
Ex: rewrite HNO3 as NO2(OH)
p = 2; pKa 8 – 5(2) 2 (exptl value is 1.4)
Ex: rewrite H3PO4 as PO(OH)3
p = 1; pKa1 8 – 5(1) 3 (exptl value is 2.1)
pKa2 8 (exptl value is 7.4)
pKa3 13 (exptl value is 12.7)
![Page 20: 1 CH4. Acids and Bases. 2 Bronsted-Lowry Bronsted-Lowry definitions: Acid = proton donor; Base = proton acceptor HF (aq) + H 2 O H 3 O + (aq) + F - (aq)](https://reader036.fdocuments.us/reader036/viewer/2022081504/56649f505503460f94c73018/html5/thumbnails/20.jpg)
20
pKa values
p Pauling pKa
calcn exptl
Cl(OH) 0 8 7.5
ClO(OH)1 3 2.0
ClO2(OH) 2 2 1.2
ClO3(OH) 3 7 ≈ 10
HlO4 + 2H2O H5IO6
![Page 21: 1 CH4. Acids and Bases. 2 Bronsted-Lowry Bronsted-Lowry definitions: Acid = proton donor; Base = proton acceptor HF (aq) + H 2 O H 3 O + (aq) + F - (aq)](https://reader036.fdocuments.us/reader036/viewer/2022081504/56649f505503460f94c73018/html5/thumbnails/21.jpg)
21
Amphoteric oxides
[Al(OH2)6]3+ Al2O3 / Al(OH)3 [Al(OH)4]
Oh Td
2 [Al(OH2)6]3+(aq) [Al2(OH2)10(OH)]5+(aq) + H3O+(aq)
pKa ~ 2 dimer
H3O+ OH
![Page 22: 1 CH4. Acids and Bases. 2 Bronsted-Lowry Bronsted-Lowry definitions: Acid = proton donor; Base = proton acceptor HF (aq) + H 2 O H 3 O + (aq) + F - (aq)](https://reader036.fdocuments.us/reader036/viewer/2022081504/56649f505503460f94c73018/html5/thumbnails/22.jpg)
22
polyoxocations
linear trimer is [Al3(OH2)14(OH)2]7+
charge/volume ratios
Al(OH2)63+ > dimer > trimer --- > Al(OH)3
3+ / Oh 5+ / 2 Oh 7+ / 3 Oh neutral
Keggin ion
[AlO4(Al(OH)2)12]7+
pH ≈ 4
![Page 23: 1 CH4. Acids and Bases. 2 Bronsted-Lowry Bronsted-Lowry definitions: Acid = proton donor; Base = proton acceptor HF (aq) + H 2 O H 3 O + (aq) + F - (aq)](https://reader036.fdocuments.us/reader036/viewer/2022081504/56649f505503460f94c73018/html5/thumbnails/23.jpg)
23
Polyoxoanions
VO43(aq) V2O5(s)
orthovanadate (Td)
2 VO43(aq) + H2O V2O7
4 (aq) + 2OH (aq)
V3O93 V3O10
5
V4O124
H3O+
oxo bridge
H3O+
H3O+
![Page 24: 1 CH4. Acids and Bases. 2 Bronsted-Lowry Bronsted-Lowry definitions: Acid = proton donor; Base = proton acceptor HF (aq) + H 2 O H 3 O + (aq) + F - (aq)](https://reader036.fdocuments.us/reader036/viewer/2022081504/56649f505503460f94c73018/html5/thumbnails/24.jpg)
24
Lewis acids and bases
A + B: A:B
LA LB complex
LA = electron pair acceptor; LB = electron pair donor
Lewis definition is more general than BL definition, does not require aqueous or protic solvent
Ex: W + 6 :CO [W(CO)6]
BCl3 + :OEt2 BCl3:OEt2
D3h
Fe3+(g) + 6 :OH2 → [Fe(OH2)6]3+
![Page 25: 1 CH4. Acids and Bases. 2 Bronsted-Lowry Bronsted-Lowry definitions: Acid = proton donor; Base = proton acceptor HF (aq) + H 2 O H 3 O + (aq) + F - (aq)](https://reader036.fdocuments.us/reader036/viewer/2022081504/56649f505503460f94c73018/html5/thumbnails/25.jpg)
25
LA/LB strengths
LA strength is based on reaction Kf
LA/LB strengths depend on specific acid base combination
Ex: BCl3 + :NR3 Cl3B:NR3
Kf: NH3 < MeNH2 < Me2NH < Me3N inductive effect
BMe3 + :NR3 Me3B:NR3
Kf: NH3 < MeNH2 < Me2NH > Me3N inductive + steric
Hrxn 58 74 81 74 kJ/mol
![Page 26: 1 CH4. Acids and Bases. 2 Bronsted-Lowry Bronsted-Lowry definitions: Acid = proton donor; Base = proton acceptor HF (aq) + H 2 O H 3 O + (aq) + F - (aq)](https://reader036.fdocuments.us/reader036/viewer/2022081504/56649f505503460f94c73018/html5/thumbnails/26.jpg)
26
log K and ligand type
![Page 27: 1 CH4. Acids and Bases. 2 Bronsted-Lowry Bronsted-Lowry definitions: Acid = proton donor; Base = proton acceptor HF (aq) + H 2 O H 3 O + (aq) + F - (aq)](https://reader036.fdocuments.us/reader036/viewer/2022081504/56649f505503460f94c73018/html5/thumbnails/27.jpg)
27
Drago-Wayland equation
A (g) + :B (g) A:B (g)
Gas phase reactions (omits solvation effects)
-Hrxn = EA EB + CA CB
look up E, C values for reactants (Table 4.4)
![Page 28: 1 CH4. Acids and Bases. 2 Bronsted-Lowry Bronsted-Lowry definitions: Acid = proton donor; Base = proton acceptor HF (aq) + H 2 O H 3 O + (aq) + F - (aq)](https://reader036.fdocuments.us/reader036/viewer/2022081504/56649f505503460f94c73018/html5/thumbnails/28.jpg)
28
Donor/Acceptor numbersCommonly used to choose appropriate solvents (Table 4.5)
Donor Number (DN) is derived from Hrxn (SbCl5 + :B Cl5Sb:B)
higher DN corresponds to stronger LB
Acceptor Number (AN) is derived from stability of Et3P=O:A complex
higher AN corresponds to stronger LA
Ex: THF (tetrahydrofuran) C4H8O
DN AN ε dielectric constant
THF 20 8 7
H2O 18 55 82
Some Li+ salts and BF3 have similar solubilities in THF, H2O
NH3 is much more soluble in H2O
Most salts are much more soluble in H2O
![Page 29: 1 CH4. Acids and Bases. 2 Bronsted-Lowry Bronsted-Lowry definitions: Acid = proton donor; Base = proton acceptor HF (aq) + H 2 O H 3 O + (aq) + F - (aq)](https://reader036.fdocuments.us/reader036/viewer/2022081504/56649f505503460f94c73018/html5/thumbnails/29.jpg)
29
Descriptive chemistry - Group 13Expect inductive effect BF3 > BCl3 > BBr3 but the opposite is true
ex: BF3 is stable in H2O, R2O (ethers)
BCl3 rapidly hydrolyzes due to nucleophilic attack of :OH2
the lower acidity of BF3 is due to unusually favorable B–X bonding in the planar conformation due to interaction
“AlCl3“ is a dimer (Al2Cl6)
General trend larger central atom, tends to have higher CN
Al2Me6 is isostructural with Al2Cl6
Friedel-Crafts
RC(O)-X: + “AlCl3” RC(O) + AlCl3X
C6H6 C6H5C(O)R
![Page 30: 1 CH4. Acids and Bases. 2 Bronsted-Lowry Bronsted-Lowry definitions: Acid = proton donor; Base = proton acceptor HF (aq) + H 2 O H 3 O + (aq) + F - (aq)](https://reader036.fdocuments.us/reader036/viewer/2022081504/56649f505503460f94c73018/html5/thumbnails/30.jpg)
30
Descriptive chemistry - Group 14
CX4 is not a Lewis Acid
Acidity SiF4 > SiCl4 > SiBr4 > SiI4 (inductive effect)
ex: 2KF(s) + SiF4(g) K2SiF6(s)
LB LA SiF62 Oh
SnF4 and PbF4 have Oh not Td coordination (heavier congener, higher CN)
each M has 2 unique axial F and 4 shared F
![Page 31: 1 CH4. Acids and Bases. 2 Bronsted-Lowry Bronsted-Lowry definitions: Acid = proton donor; Base = proton acceptor HF (aq) + H 2 O H 3 O + (aq) + F - (aq)](https://reader036.fdocuments.us/reader036/viewer/2022081504/56649f505503460f94c73018/html5/thumbnails/31.jpg)
31
Descriptive chemistry - Group 15
MF5 does not exist for nitrogen; it’s trigonal bipyramidal for M = P, As
SbF5: Sb has Oh coordination (oligomerizes to Sb4F20 or Sb6F30)
LB LA transient
K2MnF6 (s) + 2 SbF5 (l) “MnF4” + 2KSbF6 (s) F transfer
KF, H2O2 aqu HF
KMnO4 Sb2O3 MnF3 + ½ F2 (g)
Dove (1980’s), chemical synthesis of F2 gas
![Page 32: 1 CH4. Acids and Bases. 2 Bronsted-Lowry Bronsted-Lowry definitions: Acid = proton donor; Base = proton acceptor HF (aq) + H 2 O H 3 O + (aq) + F - (aq)](https://reader036.fdocuments.us/reader036/viewer/2022081504/56649f505503460f94c73018/html5/thumbnails/32.jpg)
32
Descriptive chemistry - Group 16
Inductive effect stabilizes conjugate base (anionic form)
sulfuric acid fluorosulfonic HSO3F / SbF5
pKa ~ 2 pKa ~ 5 pKa ~ 26 (superacid)
C6H6 C6H7+ SbF6
HSO3F / SbF5