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Strong/Weak Acid and Base
Strong Acid/Weak Acid
Strong acid - HI, HBr, HCI, HNO3, H2SO4, HCIO3, HCIO4
Weak Acid - CH3COOH, HF, HCN, H2CO3, H3BO3, H3PO4
Strong Base/ Weak Base
Strong base - LiOH, KOH, NaOH, CsOH, Ca(OH)2
Weak Base - NH3, C2H5NH2, (CH3)2NH, C3H5O2NH2
Distinguish bet strong and weak acid
Electrical conductivity Rate of rxn pH
Strong acid
Strong acid → High ionization → High conc H+ → High conductivity → High rate rxn → Lower pH
Strong acid
Oxoacid O atom > number ionizable proton HNO3, H2SO4, HCIO3, HCIO4
Hydrohalic acid HI, HBr, HCI
Weak acid
Hydrohalic acid HF
Oxoacid O atom ≥ number ionizable proton by 1 HCIO, HNO2, H3PO4
Carboxylic acid COOH
Strong base – contain OH- or O2-
LiOH, NaOH, CaO, K2O Ca(OH)2, Ba(OH)2
Weak base – contain electron rich nitrogen, N NH3, C2H5NH2, (CH3)2NH, C3H5O2NH2
Strong base Weak base
1 2 3
Weak acid
0.1 M HCI 0.1 M CH3COOH
H+ 0.1 mole 0.0013 mole
pH 1 (Low) 2.87 (High)
Electrical conductivity High (Ionize completely) Low (Ionize partially)
Rate with magnesium Fast Slow
Rate with calcium carbonate
Fast Slow
Weaker acid → Low ionization → Low conc H+ → Low conductivity → Low rate rxn → High pH
Strong acid
HA A- H+
H+ H+
H+
H+ H+
H+
H+ A-
A-
A-
A- A-
A-
Ionizes completely
Weak acid
HA HA
H+ A- H+
H+
A-
A- HA
HA
HA
HA
HA
HA
Ionizes partially
Easier using pH scale than Conc [H+] • Conc H+ increase 10x from 0.0001(10-4) to 0.001(10-3) - pH change by 1 unit from pH 4 to 3 • pH 3 is (10x) more acidic than pH 4 • 1 unit change in pH is 10 fold change in Conc [H+]
Conc OH- increase ↑ by 10x
pH increase ↑ by 1 unit
pOH with Conc OH-
pOH = -log [OH-] [OH-] = 0.0000001M pOH = -log [0.0000001] pOH = -log1010-7 pOH = 7 pH + pOH = 14 pH + 7 = 14 pH = 7 (Neutral)
pH with Conc H+
pH = -log [H+] [H+] = 0.0000001M pH = -log [0.0000001] pH = -log1010-7
pH = 7 (Neutral)
Conc H+ increase ↑ by 10x
pH decrease ↓ by 1 unit
pH measurement of Acidity of solution
• pH is the measure of acidity of solution in logarithmic scale • pH = power of hydrogen or minus logarithm to base ten of hydrogen ion concentration
← Acidic – pH < 7 Alkaline – pH > 7 →
pOH with Conc OH-
pOH = -log [OH-] [OH-] = 0.1M pOH = -log[0.1] pOH = 1 pH + pOH = 14 pH + 1 = 14
pH = 13 (Alkaline)
pH with Conc H+
pH = -log [H+] [H+] = 0.01M pH = -log [0.01] pH = -log1010-2
pH = 2 (Acidic)
Easier pH scale Conc H+
Formula for acid/base calculation
[OH-] [H+] Kw = [H+] x [OH-] = 1 x 10-14
[OH-] = 10-pOH pOH = -lg [OH-]
pOH pH
pH = -lg [H+] [H+] = 10-pH
pH + pOH = 14
Formula for acid/base calculation
Dissociation Constant for Weak Acid
pH = -log10[H+] pOH = -log10[OH-]
pH + pOH = 14 pH + pOH = pKw
Kw = [H+][OH-] Ka x Kb = Kw
Ka x Kb = 1 x 10-14
pKa = - lg10Ka pKb = - lg10Kb
pKa + pKb = pKw
pKa + pKb = 14
AHHA
HA
AHKa
HCOOCHCOOHCH 33
COOHCH
H
COOHCH
HCOOCHKa
3
2
3
3
Dissociation Constant for Weak Base
OHBHOHB 2
B
OHBHKb
OHNHOHNH 423
3
2
3
4
NH
OH
NH
OHNHKb
OHCOOCHOHCOOHCH 3323
OHCOOCHOHCOOHCH 3323
COOHCH
OHCOOCHKa
3
33
OHCOOHCHOHCOOCH 323
COOCH
OHCOOHCHKb
3
3
Derive Ka x Kb = Kw
Relationship bet Weak acid and its conjugate base
Weak acid Conjugate Base
COOCH
OHCOOHCH
COOHCH
OHCOOCH
3
3
3
33
OHOHCOOCH
OHCOOHCH
COOHCH
OHCOOCH3
3
3
3
33
wba KKK
Formula for acid/base calculation
Ka /Kb measure equilibrium position Ka/Kb large ↑ – ↑ dissociation – shift to right – favour product Ka/Kb large ↑ – pKa /pKb small ↓ – Stronger acid/base
Strong acid Large ↑ Ka
Weak acid Small ↓ Ka
Strong base Large ↑ Kb
Weak base Small ↓Kb
↑ Ka → ↓ pKa
Ka /Kb measure equilibrium position Ka /Kb small ↓ – ↓ dissociation – shift to left – reactant favour Ka /Kb small ↓ – pKa /pKb high ↑– Weak acid/base
↑ Kb → ↓ pKb
↓ Ka → ↑ pKa
↓ Kb →↑ pKb
For weak acid/ base
CIHHCI OHNHOHNH 423
Shift right Shift left
CH3COOH + H2O ↔ CH3COO- + H3O+
CH3COOH CH3COO- CH3COOH ↔ CH3COO- Strong Acid Weak conjugate Base Conjugate acid base pair
Small dissociation constant
Strong Acid Weak base
ba KK /
Str
ong a
cid
Stro
ng b
ase
Formula for acid/base calculation
[OH-] [H+] Kw = [H+] x [OH-] = 1 x 10-14
[OH-] = 10-pOH pOH = -lg [OH-]
pOH pH
pH = -lg [H+] [H+] = 10-pH
pH + pOH = 14
Formula for acid/base calculation
Dissociation Constant for Weak Acid
pH = -log10[H+] pOH = -log10[OH-]
pH + pOH = 14 pH + pOH = pKw
Kw = [H+][OH-] Ka x Kb = Kw
Ka x Kb = 1 x 10-14
pKa = - lg10Ka pKb = - lg10Kb
pKa + pKb = pKw
pKa + pKb = 14
AHHA
HA
AHKa
HCOOCHCOOHCH 33
COOHCH
H
COOHCH
HCOOCHKa
3
2
3
3
Dissociation Constant for Weak Base
OHBHOHB 2
B
OHBHKb
OHNHOHNH 423
3
2
3
4
NH
OH
NH
OHNHKb
Dissociate partially ↔ used
Weak acid/base
Ka /Kb value pKa /pKb value easier!
Click here weak acid dissociation Click here weak acid dissociation Click here CH3COOH dissociation Click here strong acid ionization
Weak acid/base Animation
NH3 ↔ NH4+
Buffer Solution
Acid part
Neutralize
each other
Salt part
Base part
- NH3(weak base) + NH4CI (salt) - NH3 + H2O ↔ NH4
+ + OH− → NH3 molecule neutralise added H+ - NH4CI → NH4
+ + CI− → NH4+ neutralise added OH−
- Effective buffer equal amt weak base NH3 and conjugate acid NH4+
Acidic Buffer Basic Buffer
Resist a change in pH when small amt acid/base is added.
CH3COOH + H2O ↔ CH3COO- + H3O+
Acidic Buffer - weak acid and its salt/conjugate base
CH3COOH ↔ CH3COO-
Conjugate acid base pair
CH3COOH CH3COO-
Weak Acid Conjugate Base
BUFFER
Dissociate fully
HCOOCHCOOHCH 33
COOHCH3 COONaCH3
NaCOOCHCOONaCH 33
Dissociate partially
- CH3COOH (weak acid) + CH3COONa (salt) - CH3COOH ↔ CH3COO- + H+ → CH3COOH neutralise added OH− - CH3COONa → CH3COO- + Na+ → CH3COO- neutralise added H+ - Effective buffer equal amt weak acid CH3COOH and base CH3COO-
COOHCH3
COOCH3BUFFER
Add acid H+ Add alkaline OH-
Neutralize
each other
Basic buffer - weak base and its salt/conjugate acid
OHNHOHNH 423
NH3 + H2O ↔ NH4+ + OH-
NH3
Weak Base
NH4+
Conjugate acid
CINH 43NH
BUFFER
Conjugate acid base pair
Add acid H+ Add alkaline OH-
Neutralize
each other
Neutralize
each other
Dissociate partially
CINHCINH 44
3NH
4NH
Base part Salt part
Acid part
Dissociate fully
BUFFER
How to prepare acidic/ basic buffer
Acid Dissociation constant CH3COOH + H2O ↔ CH3COO- + H3O+
Ka = (CH3COO-) (H3O+) (CH3COOH) -lgKa = -lgH+ -lg (CH3COO-) (CH3COOH) -lgH+ = -lg Ka + lg (CH3COO-) (CH3COOH) pH = pKa + lg (CH3COO-) (CH3COOH)
Acidic Buffer Formula • Mixture Weak acid + Salt/Conjugate base • CH3COOH ↔ CH3COO- + H+ (dissociate partially)
• CH3COONa → CH3COO- + Na+ (dissociate fully)
Basic Buffer Formula • Mixture Weak base + Salt/Conjugate acid • NH3 + H2O ↔ NH4
+ + OH_ (dissociate partially)
• NH4CI → NH4+ + CI_ (dissociate fully)
pH = pKa - lg (acid) (salt)
pH = pKa + lg (salt) (acid)
Base Dissociation constant NH3 + H2O ↔ NH4
+ + OH-
Kb = (NH4+) (OH-)
(NH3) -lgKb = -lgOH- -lg (NH4
+) (NH3) -lgOH- = -lgKb + lg (NH4
+) (NH3) pOH = pKb + lg (NH4
+) (NH3)
pOH = pKb + lg (salt) (base)
pOH = pKb - lg (base) (salt)
Basic Buffer Acidic Buffer
salt salt
acid base
Henderson Hasselbalch Equation
multiply -lg both sides
Henderson Hasselbalch Equation
Basic Buffer Preparation Acidic Buffer Preparation
Prepare Acidic Buffer pH = 5.2 • Choose pKa acid closest to pH 5.2 • pKa = 4.74 (ethanoic acid) chosen • pH = pKa -lg [acid] [salt] • 5.2 = 4.74 – lg [acid] [salt] • [acid] = 0.35 [salt] Ratio of [acid] = 0.35 [salt]
Use same conc acid/salt but different vol ratio • 1M, 35ml (acid) = 0.35 or 0.1M, 35ml (acid) = 0.35 1M, 100ml (salt) 0.1M, 100ml (salt)
Use same vol acid/salt but different conc ratio • 3.5M, 10ml (acid) = 0.35 or 0.35M, 10ml (acid) = 0.35 10M, 10ml (salt) 1M, 10ml (salt)
Buffer capacity • Adding water will not change the pH of acidic buffer • Ratio of acid/salt still the same • Ka acid remain same
Prepare Basic Buffer pH = 9.5 or pOH = 4.5 • Choose pKb base closest to pOH = 4.5 • pKb = 4.74 (NH3) chosen • pOH = pKb -lg [base] [salt] • 4.5 = 4.74 – lg [base] [salt] • [base] = 1.74 [salt] Ratio of [base] = 1.74 [salt]
Use same conc base/salt but different vol ratio • 1M, 174ml (base) = 1.74 or 0.1M, 174ml (base) = 1.74 1M, 100ml (salt) 0.1M, 100ml (salt)
Use same vol base/salt but different conc ratio • 1.74M, 10ml (base) = 1.74 or 0.174M, 10ml (base) = 1.74 1M, 10ml (salt) 0.1M, 10ml (salt)
Buffer capacity • Adding water will not change the pH of basic buffer • Ratio of base/salt still the same • Kb base remain same
Buffer solution
Buffer Preparation
1 1
2 2
3 Use fix vol, 1dm3 and use different mole ratio (Acid/salt) • 0.35 mole acid + 1 mole salt to 1 dm3 solvent = 0.35
Use fix vol, 1dm3 and use different mole ratio (base/salt) • 1.74 mole base + 1 mole salt to 1 dm3 solvent = 1.74
3
3 ways to prepare buffer 3 ways to prepare buffer
Basic Buffer Preparation Acidic Buffer Preparation
Prepare Acidic Buffer pH = 5.2 • Choose pKa acid closest to pH 5.2 • pKa = 4.74 (ethanoic acid) chosen • pH = pKa -lg [acid] [salt] • 5.2 = 4.74 – lg [acid] [salt] • [acid] = 0.35 [salt] Ratio of [acid] = 0.35 [salt]
Use same conc acid/salt but different vol ratio Buffer A Buffer B • 1M, 35ml (acid) = 0.35 or 0.1M, 35ml (acid) = 0.35 1M, 100ml (salt) 0.1M, 100ml (salt)
Prepare Basic Buffer pH = 9.5 or pOH = 4.5 • Choose pKb base closest to pOH = 4.5 • pKb = 4.74 (NH3) chosen • pOH = pKb -lg [base] [salt] • 4.5 = 4.74 – lg [base] [salt] • [base] = 1.74 [salt] Ratio of [base] = 1.74 [salt]
Use same conc base/salt but different vol ratio Buffer A Buffer B • 1M, 174ml (base) = 1.74 or 0.1M, 174ml (base) = 1.74 1M, 100ml (salt) 0.1M, 100ml (salt)
Buffer solution
Buffering Capacity
1 1
1M, 35ml
(acid) 1M, 100ml
(salt)
0.1M, 35ml
(acid)
0.1M, 100ml
(salt)
B A
1M, 174ml
(base)
1M, 100ml
(salt)
0.1M, 174ml (base)
0.1M, 100ml (salt)
B A
Buffer A > Buffer B Stronger buffering capacity
• Amt of acid/salt higher to neutralise added H+ or OH-
• Ratio acid/salt same, pH buffer same but buffering capacity diff • Higher buffer conc – Higher buffering capacity
Buffer A > Buffer B Stronger buffering capacity
• Amt of base/salt higher to neutralise added H+ or OH-
• Ratio acid/salt same, pH buffer same but buffering capacity diff • Higher buffer conc – Higher buffering capacity
Which has greater buffering capacity ? Which has greater buffering capacity ?
Basic Buffer Preparation Acidic Buffer Preparation
Prepare Acidic Buffer pH = 5.2 • Choose pKa acid closest to pH 5.2 • pKa = 4.74 (ethanoic acid) chosen • pH = pKa -lg [acid] [salt] • 5.2 = 4.74 – lg [acid] [salt] • [acid] = 0.35 [salt] Ratio of [acid] = 0.35 [salt]
Prepare Basic Buffer at pH = 9.5 or pOH = 4.5 • Choose pKb base closest to pOH = 4.5 • pKb = 4.74 (NH3) chosen • pOH = pKb -lg [base] [salt] • 4.5 = 4.74 – lg [base] [salt] • [base] = 1.74 [salt] Ratio of [base] = 1.74 [salt]
Buffer solution
Buffering Capacity
2 2
3.5M, 10ml
(acid)
10M, 10ml
(salt) 0.35M, 10ml
(acid)
1M, 10ml
(salt)
B A
1.74M, 10ml
(base)
1M, 10ml
(salt)
0.174M, 10ml (base)
0.1M, 10ml (salt)
B A
Use same vol acid/salt but different conc ratio Buffer A Buffer B • 3.5M, 10ml (acid) = 0.35 or 0.35M, 10ml (acid) = 0.35 10M, 10ml (salt) 1M, 10ml (salt)
Use same vol base/salt but different conc ratio Buffer A Buffer B • 1.74M, 10ml (base) = 1.74 or 0.174M, 10ml (base) = 1.74 1M, 10ml (salt) 0.10M, 10ml (salt)
Which has greater buffering capacity ? Which has greater buffering capacity ?
Buffer A > Buffer B Stronger buffering capacity
• Amt of acid/salt higher to neutralise added H+ or OH-
• Ratio acid/salt same, pH buffer same but buffering capacity diff • Higher buffer conc – Higher buffering capacity
Buffer A > Buffer B Stronger buffering capacity
• Amt of base/salt higher to neutralise added H+ or OH-
• Ratio acid/salt same, pH buffer same but buffering capacity diff • Higher buffer conc – Higher buffering capacity
Basic Buffer Preparation Acidic Buffer Preparation
Buffer solution
Buffering Capacity
3 3
0.35mol
(acid ) 1mol
(salt) 0.035mol
(acid)
0.10mol
(salt)
B A
1.74mol
(base)
1mol
(salt)
0.174mol (base)
0.1mol (salt)
B A
Use fix vol, 1dm3 but diff mole ratio (acid/salt) Buffer A Buffer B • 0.35mol (acid) = 0.35 or 0.035mol (acid) = 0.35 1mol (salt) 0.1mol (salt)
1dm3 1dm3 1dm3 1dm3
Use fix vol, 1dm3 but diff mole ratio (base/salt) Buffer A Buffer B • 1.74mol (base) = 1.74 or 0.174mol (base) = 1.74 1mol (salt) 0.1mol (salt)
Which has greater buffering capacity ? Which has greater buffering capacity ?
Prepare Acidic Buffer pH = 5.2 • Choose pKa acid closest to pH 5.2 • pKa = 4.74 (ethanoic acid) chosen • pH = pKa -lg [acid] [salt] • 5.2 = 4.74 – lg [acid] [salt] • [acid] = 0.35 [salt] Ratio of [acid] = 0.35 [salt]
Prepare Basic Buffer at pH = 9.5 or pOH = 4.5 • Choose pKb base closest to pOH = 4.5 • pKb = 4.74 (NH3) chosen • pOH = pKb -lg [base] [salt] • 4.5 = 4.74 – lg [base] [salt] • [base] = 1.74 [salt] Ratio of [base] = 1.74 [salt]
Buffer A > Buffer B Stronger buffering capacity
• Amt of acid/salt higher to neutralise added H+ or OH-
• Ratio acid/salt same, pH buffer same but buffering capacity diff • Higher buffer conc – Higher buffering capacity
Buffer A > Buffer B Stronger buffering capacity
• Amt of base/salt higher to neutralise added H+ or OH-
• Ratio acid/salt same, pH buffer same but buffering capacity diff • Higher buffer conc – Higher buffering capacity
Basic Buffer Preparation Acidic Buffer Preparation
Prepare Acidic Buffer at pH = 5.2 • Choose pKa acid closest to pH 5.2 • pKa = 4.74 (ethanoic acid) chosen • pH = pKa -lg [acid] [salt] • 5.2 = 4.74 – lg [acid] [salt] • [acid] = 0.35 [salt] Ratio of [acid] = 0.35 [salt]
Prepare Basic Buffer pH = 9.5 or pOH = 4.5 • Choose pKb base closest to pOH = 4.5 • pKb = 4.74 (NH3) chosen • pOH = pKb -lg [base] [salt] • 4.5 = 4.74 – lg [base] [salt] • [base] = 1.74 [salt] Ratio of [base] = 1.74 [salt]
Buffer solution
Buffering Capacity
4 4
Will pH change by adding water?
pH Buffer A = pH Buffer B • Same pH • Adding water will not change pH • Amt of acid/salt still the same • Ratio conc acid/salt same, pH buffer same
0.35mol
(acid)
1mol
(salt )
0.35mol
(acid )
1mol
(salt)
B A 1.74mol
(base)
1mol
(salt) 1.74mol (base)
1mol (salt)
B A
Same mole ratio (acid/salt) but different total volume Buffer A Buffer B • 0.35mol (acid )= 0.35 in 1dm3 or 0.35mol (acid) = 0.35 in 2dm3
1mol (salt) 1mol (salt)
1dm3
2dm3
1dm3
Same mole ratio (base/salt) but different total volume Buffer A Buffer B • 1.74mol (base) = 1.74 in 1dm3 or 1.74mol (base) = 1.74 in 2dm3
1mol (salt) 1mol (salt)
2dm3
Add Water
Will pH change by adding water?
Add Water
pH Buffer A = pH Buffer B • Same pH • Adding water will not change pH • Amt of acid/salt still the same • Ratio conc acid/salt same, pH buffer same
Weaker buffering capacity
Acidic Buffer Preparation Acidic Buffer Preparation
Prepare Acidic Buffer pH = 4.74 • Choose pKa acid closest to pH 4.74 • pKa = 4.74 (ethanoic acid) chosen • pH = pKa -lg [acid] [salt] • 4.74 = 4.74 – lg [acid] [salt] • [acid] = 1.00 [salt] Ratio of [acid] = 1.00 [salt]
Buffer solution
Buffering Capacity
5 5
Which has greater buffering capacity ?
Buffer A > Buffer B • Conc ratio [acid]/[salt] = 1 • Buffer highest buffering capacity when pH = pKa • Conc acid = Conc salt → highest buffering capacity
Concentration ratio [acid]/[salt] = 1
1 mol
(acid)
1 mol
(salt)
A
1 mol
(salt)
B
Buffer A > Buffer B • Further conc ratio [acid]/[salt] from 1
Same conc ratio (acid/salt) in 1dm3 Buffer A
• 1 mol (acid ) = 1.00 1 mol (salt)
1dm3 1dm3
Prepare Acidic Buffer at pH = 5.2 • Choose pKa acid closest to pH 5.2 • pKa = 4.74 (ethanoic acid) chosen • pH = pKa -lg [acid] [salt] • 5.2 = 4.74 – lg [acid] [salt] • [acid] = 0.35 [salt] Ratio of [acid] = 0.35 [salt]
Different conc ratio (acid/salt) in 1dm3 Buffer B
• 0.35mol (acid ) = 0.35 1.00mol (salt)
Which has greater buffering capacity ?
0.35mol
(acid)
Concentration ratio [acid]/[salt] ratio < 1
Lower buffering capacity
No Salt Hydrolysis
Presence of ions from salt cause bonds in water to break
NEUTRALIZATION
HCI + NaOH → NaCI + H2O
Neutral salt
Strong acid and Strong base
NaCI – Ionize - Na+ and CI- ion – Na+ doesn’t cause water hydrolysis - No breaking bond in water.
Strong acid and Weak base Weak acid and Strong base
HCI + NH4OH → NH4CI + H2O CH3COOH + NaOH → CH3COONa + H2O
Acidic salt Basic salt
Salt Hydrolysis Salt Hydrolysis
No breaking
bond in water
NH4CI – Ionize - NH4+ and CI- ion
- NH4+ cause water hydrolysis
- Breaking bond in water
NH4+ + H2O ↔ NH3 + H3O+
CH3COONa – Ionize - Na+ and CH3COO- ion - CH3COO- cause water hydrolysis - Breaking bond in water
CH3COO- + H2O ↔ CH3COOH + OH-
NH4+ (Acid) - NH3 (Conjugate base)
lose H+ to produce H+ gain H+ to produce OH-
CH3COO- (Base) - CH3COOH (Conjugate acid)
NH4+ + H2O → NH3 + H3O
+
NH4CI → NH4+ + CI-
H3O+ (Acidic)
Cation hydrolysis Anion hydrolysis
CH3COONa → CH3COO- + Na+
CH3COO- + H2O→ CH3 COOH + OH-
OH- (Alkaline)
NaCI → Na+ + CI-
No H2O hydrolysis
H2O (Neutral)
NEUTRALIZATION
Neutral salt
Strong acid and Strong base Strong acid and Weak base Weak acid and Strong base
Acidic salt Basic salt
NH4+ + H2O ↔ NH3 + H3O+ CH3COO- + H2O ↔ CH3COOH + OH-
lose H+ to produce H+ gain H+ to produce OH-
NH4+ + H2O → NH3 + H3O
+
NH4CI → NH4+ + CI-
H3O+ (Acidic)
Cation hydrolysis Anion hydrolysis
CH3COONa → CH3COO- + Na+
CH3COO- + H2O→ CH3 COOH + OH-
OH- (Alkaline)
NaCI → Na+ + CI-
No H2O hydrolysis
H2O (Neutral)
HCI + NaOH → NaCI + H2O
Neutralization Reaction Salt Salt hydrolysis Type salt pH salt
Strong acid +
Strong base
HCI +
NaOH
NaCI
No hydrolysis Neutral salt 7
Strong acid +
Weak base
HCI +
NH3
NH4CI
Cation hydrolysis
Acidic salt < 7
Weak acid +
Strong base
CH3COOH +
NaOH
CH3COONa
Anion hydrolysis
Basic salt > 7
Weak acid +
Weak base
CH3COOH +
NH3
CH3COONH4
Anion/Cation hydrolysis
Depends ?
Click here on acidic buffer simulation
Click here buffer simulation
CH3COO- + H2O → CH3 COOH + OH-
Salt Hydrolysis
Neutralization Reaction Salt Salt hydrolysis Type salt pH salt
Strong acid +
Strong base
HCI +
NaOH
NaCI
No hydrolysis Neutral salt 7
Strong acid +
Weak base
HCI +
NH3
NH4CI
Cation hydrolysis
Acidic salt < 7
Weak acid +
Strong base
CH3COOH +
NaOH
CH3COONa
Anion hydrolysis
Basic salt > 7
Weak acid +
Weak base
CH3COOH +
NH3
CH3COONH4
Anion/Cation hydrolysis
Depends ?
Weak acid and Weak base
CH3COOH + NH3 → CH3COONH4
Acidicity depend on Ka and Kb
Ka > Kb – Acidic – H+ ions produced Kb < Ka – Basic – OH- ions produced Ka = Kb – Neutral – hydrolyzed same extent.
CH3COONH4 → CH3COO- + NH4+
NH4+ + H2O → NH3 + H3O
+
salt
anion cation
OH- - Basic H3O+ - Acidic Kb Ka
Ka = Kb
NEUTRAL
NH3 + HF → NH4F
salt
NH4F → NH4+ + F-
NH4+ + H2O → NH3 + H3O
+ F- + H2O → HF + OH-
cation anion
Ka H3O
+ - Acidic Kb OH- - Basic
Acidicity depend on Ka and Kb
Ka > Kb – Acidic – H+ ions produced Kb < Ka – Basic – OH- ions produced Ka = Kb – Neutral – hydrolyzed same extent.
Kb > Ka
BASIC
Weak acid
+
Weak base
gain H+ to produce OH- - Basic lose H+ to produce H3O+ - Acidic
CH3COO- + H2O → CH3 COOH + OH-
Dissociation constant Ka and Kb
Weak acid and Weak base
CH3COOH + NH3 → CH3COONH4
CH3COONH4 → CH3COO- + NH4+
NH4+ + H2O → NH3 + H3O
+
salt
anion cation
OH- - Basic H3O+ - Acidic Kb Ka
Ka = Kb NEUTRAL
NH3 + HF → NH4F
salt
NH4F → NH4+ + F-
NH4+ + H2O → NH3 + H3O
+ F- + H2O → HF + OH-
cation anion
Ka H3O
+ - Acidic Kb OH- - Basic
Kb > Ka BASIC
Amphoteric Ion
Ka = 4.7 x 10 -11 Kb = 2.3 x 10 -8
HCO3- + H2O ↔ H3O
+ + CO32- HCO3
- + H2O ↔ H2CO3 + OH-
Kb > Ka
BASIC
Solution of HCO3- - Acidic or alkaline?
Solution of H2PO4- - Acidic or alkaline?
H2PO4- + H2O ↔ HPO4
2- + H3O+ H2PO4
- + H2O ↔ H3PO4 + OH-
lose H+ to produce H3O+ - Acidic
Ka = 6.2 x 10 -8
gain H+ to produce OH- - Basic
Kb = 1.4 x 10 -12
Ka > Kb
ACIDIC
IB QUESTIONS
Predict for each salt whether pH is <, >, = 7
1
HCI + Fe(OH)3 → FeCI3
strong acid + weak base → acidic salt
HNO3 + NH4OH → NH4NO3
NaNO3
strong acid + weak base → acidic salt
H2CO3 + NaOH → Na2CO3
Weak acid + strong base → basic salt
NH4NO3 FeCI3 Na2CO3
CH3COOLi KCN
HNO3 + NaOH → Na2CO3
strong acid + strong base → neutral salt
CH3COOH + LiOH → CH3COOLi HCN + KOH → KCN
2 3
pH < 7 pH > 7 pH < 7
Predict for each salt whether pH is <, >, = 7
Weak acid + strong base → basic salt
pH > 7 pH = 7
Weak acid + strong base → basic salt
pH > 7 Deduce the pH of solution
4 5 6
H2SO4 + NH3 → ? H3PO4 + KOH → ? HNO3 + Ba(OH)2 → ? 7 8 9
strong acid + weak base → acidic salt
pH < 7
Weak acid + strong base → basic salt
pH > 7
strong acid + strong base → neutral salt
pH = 7
Acidic Buffer Calculation
Find pH buffer - 0.20 mol CH3COONa(salt) add to 0.5dm3, 0.10M CH3COOH(acid) Ka = 1.8 x 10-5
Conc CH3COO- = Moles/volume = 0.20/0.5 = 0.40M
Click here videos Khan Academy
Find conc of CH3COONa(salt) added to 1.0dm3 of 1.0M CH3COOH(acid) Ka = 1.8 x 10-5M, pKa = 4.74 , pH 4.5
Find pH buffer - 0.10M CH3COOH(acid), 0.25M CH3COONa(salt) Ka = 1.8 x 10-5
1st method (formula)
1
Convert Ka to pKa
2nd method (Ka)
2
1st method (formula) Convert Ka to pKa
2nd method (Ka)
3
1st method (formula)
Conc salt
2nd method (Ka)
Click here explanation from chem guide
14.5
]25.0[
]10.0[lg74.4
][
][lg
pH
pH
salt
acidpKpH a
14.5
)102.7lg(
)lg(
102.7
10.0
))(25.0(108.1
)(
))((
6
6
5
3
3
pH
pH
HpH
H
H
COOHCH
HCOOCHK a
34.5
]40.0[
]10.0[lg74.4
][
][lg
pH
pH
salt
acidpKpH a
74.4
)108.1lg(
lg
108.1
5
5
a
a
aa
a
pK
pK
KpK
K
74.4
)108.1lg(
lg
108.1
5
5
a
a
aa
a
pK
pK
KpK
K
MCOOCH
COOCH
COOHCH
HCOOCHK a
0578.0
0.1
)1016.3)((108.1
)(
))((
3
5
35
3
3
Msalt
salt
salt
salt
acidpKpH a
0578.0][
24.0][
]0.1[lg
][
]0.1[lg74.45.4
][
][lg
34.5
)105.4lg(
)lg(
105.4
10.0
))(40.0(108.1
)(
))((
6
6
5
3
3
pH
pH
HpH
H
H
COOHCH
HCOOCHK a
51016.3
)lg(5.4
)lg(
H
H
HpH
Conc [H+]
Find pH buffer - 0.50M NH3 (base), 0.32M NH4CI (salt) Kb = 1.8 x 10-5
Basic Buffer Calculation
Find pH buffer - 4.28g NH4CI (salt) add to 0.25dm3, 0.50NH3(base) Kb = 1.8 x 10-5
Mole NH4CI = mass/RMM = 4.28 / 53.5 = 0.08 mol
Conc NH4CI = moles/vol = 0.08/0.25 = 0.32M
4
1st method (formula) 2nd method (Kb)
1st method (formula)
5
2nd method (Kb) Conc salt
Find mass of CH3COONa added to 500ml, 0.10M CH3COOH(acid) pH = 4.5, Ka = 1.8 x 10-5M, pKa = 4.74
Conc CH3COO- = 0.0578M → x RMM (82) → 4.74g in 1000ml 2.37g in 500ml
6
2nd method (Ka) 1st method (formula)
Click here addition base to buffer
Click here addition acid to buffer
45.955.414
55.4
]32.0[
]50.0[lg74.4
][
][lg
pH
pOH
pOH
salt
basepKpOH b
45.955.414
55.4
)1081.2lg(
)lg(
5
pH
pOH
pOH
OHpOH
5
5
3
4
423
1081.2
50.0
))(32.0(108.1
)(
))((
OH
OH
NH
OHNHK
OHNHOHNH
b
45.955.414
55.4
]32.0[
]50.0[lg74.4
][
][lg
pH
pOH
pOH
salt
basepKpOH b
45.955.414
55.4
)1081.2lg(
)lg(
5
pH
pOH
pOH
OHpOH
5
5
3
4
423
1081.2
50.0
))(32.0(108.1
)(
))((
OH
OH
NH
OHNHK
OHNHOHNH
b
0578.0][
24.0][
]10.0[lg
][
]10.0[lg74.45.4
][
][lg
3
3
3
3
COOCH
COOCH
COOCH
COOCH
acidpKpH a
5.410
)lg(5.4
)lg(
H
H
HpH
MCOOCH
COOCH
COOHCH
HCOOCHK
HCOOCHCOOHCH
a
0578.0][
)10.0(
)10)((108.1
)(
))((
3
5.4
35
3
3
33
Conc [H+]
Bicarbonate buffering system
Click here view buffering
Concept Map Buffer
pH
Proton availability Stable
Buffer solution
Weak acid ↔ Conjugate base
][
][lg
salt
acidpKpH a
pH = -lg[H+]
made up of
HA ↔ H+ + A-
Weak base ↔ Conjugate acid
or
Buffering capacity highest
Buffer formula
pH = pKa
1][
][
baseConjugate
Acid
B + H2O ↔ BH+ + OH-
or
Ratio of acid base
Dilution Add water
pH buffer
pH will not change
Temperature affect pH
pH change
Basic Buffering system in blood
CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3-
Acid base homeostasis - pH blood plasma constant - buffer range 7.0 – 7.45
Increase CO2 – Shift right – More H+ – pH ↓ - Acidic
Decrease CO2 – Shift left – Less H+ - pH ↑ - Alkaline
H2CO3 ↔ HCO3-
Weak acid Conjugate base
Exercise - release lactic acid H+/CO2
HCO3- – base neutralize added acid
Respiratory acidosis (Hypoventilation)
Breathing too slowly – More CO2 in blood – pH ↓– Acidic
HCO3- reabsorb/secretion by kidney, neutralize H+
Respiratory alkalosis (Hyperventilation)
Breathing too fast – Less CO2 in blood – pH ↑– Alkaline
Release of H+ by kidney to reduce pH ↓
HCO3- secretion by kidney to reduce pH ↓
Altitude Sickness (Hyperventilation)
High altitude – [O2] ↓ – Hyperventilate ↑ – Less CO2 blood ↓ - pH ↑
Drug stimulate secretion HCO3- / increase H+ secretion by kidney
Click here on pH calculation
Video on Acid/ Base
Click here on pKa /pKb calculation How pH = pOH = 14 derived How Ka x Kb = Kw derived
Simulation on Acid/ Base
Click here on pH animation Click here to acid/base simulation
Click here on weak base simulation Click here strong acid ionization Click here on weak acid dissociation