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