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Prepared by
Lawrence Kok
Tutorial on Indicators and Salt Hydrolysis.
Acid Base Indicators
Indicators • Organic dye of weak acid/weak base with pKa/pKb value• Detect equivalence pt in titration• HIn as indicator have 2 diff colour in acidic/alkaline medium
HIn ↔ H+ + In-
(red) (blue)
HIn ↔ H+ + In-
(H+ ion ↑) - Equilibrium shift to leftMore [HIn ] → red , [HIn] > [In-]
HIn ↔ H+ + In-
(H+ ion ↓) - Equilibrium shift to rightMore [In- ] → blue, [In-] > [HIn]
Indicator pKa pH range
ColourAcid
ColourBase
Methyl orange 3.46 3.2- 4.4 RED Yellow
Bromophenol Blue 4.10 3.0- 4.6 Yellow Blue
Bromocresol Green 4.90 3.8- 5.4 Yellow Blue
Methyl Red 5.00 4.8- 6.0 Red Yellow
Bromothymol Blue 7.30 6.0- 7.6 Yellow Blue
Phenol Red 8.00 6.6- 8.2 Yellow Red
Phenolphthalein 9.50 8.2-10.0 Colourless Pink
acid base
Presence of base, OH-Presence of acid, H+
HIn ↔H+ + In-
(red) (blue)
Ka = (H+)(In-)(HIn)
(HIn) = (H+)(In-) Ka
H+ = Ka
-lgH+ = -lg Ka
pH = pKa
↔ ↔Presence of acid, H+ Presence of base, OH-
[HIn] > [In-]RED
[In-] > [HIn]BLUE
HIn = In- → pH = pKa → Two colour red/blue have equal conc,Indicator have colour in bet red and blue (start to change colour)
[HIn] = [In-]Equivalence Pt
Start to change colour
HIn ↔H+ + In-HIn In-
[HIn] = [In-]RED + BlUE
x log
both side
Click here indicator note chem guideClick here detail acid/base note
HIn In-
• Indicator change colour at its pKa but cannot be detected by our eyes• pH range – Indicator change colour over a range of pH• Methyl orange, pKa is 3.46 but change colour in range of pH (3.2 - 4.4)• pH range (pH = pKa ± 1) seen by our eye• Indicator must only change colour at equivalence pt• End point of indicator must correspond/coincide with equivalence pt• Colour change must occur rapidly at equivalence pt• Indicator change colour over a region of 2 pH units centered on pKa
Acid Base Indicators
Indicator pKa pH range
ColourAcid
ColourBase
Methyl orange 3.46 3.2- 4.4 RED Yellow
Bromophenol Blue 4.10 3.0- 4.6 Yellow Blue
Bromocresol Green 4.90 3.8- 5.4 Yellow Blue
Indicator pKa pH range
ColourAcid
ColourBase
Methyl orange 3.46 3.2- 4.4 RED Yellow
pH 1 pH 4.4
Acid Base
Methyl Orange
Indicator pKa pH range
ColourAcid
ColourBase
Phenol Red 8.00 6.6- 8.2 Yellow Pink
Base
Phenol Red
pH 1 pH 6.6 pH 8.2 pH 14
Acid
pH 14pH 3.2
Equivalence Point End Point
Amt of acid = Amt base (Neutralization)
Indicator changecolour
pKa – 3.46
Eye cannot detect
Eye cannot detect
HIn ↔ H+ + In-
(red) (yellow)
HIn ↔ H+ + In-
(yellow) (pink)
Indicator pKa pH range
ColourAcid
ColourBase
Bromothymol Blue 7.30 6.0- 7.6 Yellow Blue
Phenol Red 8.00 6.6- 8.2 Yellow Pink
Phenolphthalein 9.50 8.2- 10.0 Colourless Pink
Acid Base Indicators
Indicator pKa pH range
ColourAcid
ColourBase
Methyl orange 3.46 3.2- 4.4 RED Yellow
pH range
(3.2 – 4.4)
pH 1 pH 4.43.46
pH range – change colour over a range of pH, - always include pKa
Acid Base
Methyl Orange
Indicator pKa pH range
ColourAcid
ColourBase
Phenol Red 8.00 6.6- 8.2 Yellow Pink
Base
Phenol Red
pH 1 pH 6.6 pH 8.2 pH 14
pH range
(6.6 – 8.0)
Acid
8
Indicator changes colour at its pKa
Indicator do not change colour at pH 7
pH 14pH 3.2
Equivalence Point End Point
Amt of acid = Amt base (Neutralization)
Indicator changecolour
• Indicator change colour at its pKa but cannot be detected by our eyes• pH range – Indicator change colour over a range of pH• Methyl orange, pKa is 3.46 but change colour in range of pH (3.2 - 4.4)• pH range (pH = pKa ± 1) seen by our eye• Indicator must only change colour at equivalence pt• End point of indicator must correspond/coincide with equivalence pt• Colour change must occur rapidly at equivalence pt• Indicator change colour over a region of 2 pH units centered on pKa
HIn ↔ H+ + In-
(red) (yellow)
pH range – change colour over a range of pH, - always include pKa
HIn ↔ H+ + In-
(yellow) (pimk)
Indicator change colour at its pKa
Indicator do not change colour at pH 7
Indicator pKa pH range
ColourAcid
ColourBase
Methyl orange 3.46 3.2- 4.4 RED Yellow
Bromophenol Blue 4.10 3.0- 4.6 Yellow Blue
Bromocresol Green 4.90 3.8- 5.4 Yellow Blue
Indicator pKa pH range
ColourAcid
ColourBase
Phenol Red 8.00 6.6- 8.2 Yellow Pink
Phenolphthalein 9.50 8.2- 10.0 Colourless Pink
Indicator ColourAcid
pKa pH range ColourBase
HIn RED 4.5 3.5 – 5.5 BLUE
Acid Base Indicators
pH 1 pH 3.5 4.5 pH 5.5 pH 14
Indicator change
colour at pKa
Range of pH indicator
change colour
HIn ↔ HIn ↔H+ + In- ↔ In-
[HIn] = [In-]RED + BLUE
pH = 4.5 → pKa of HIn, indicator change colour (End point) from red to blue• Red turn blue but cannot be detected by our eyes• Indicator change colour over a region of 2 pH units centerd on pKa
HIn ↔H+ + In-
(red) (Blue)
Ka = (H+)(In-)(HIn)
(H+) = (HIn) Ka (In-)
H+ = Ka
-lgH+ = -lg Ka
pH = pKa
pH = 4.5 (pKa of indicator)
[HIn] = 10[In-] 1[HIn] > [In-] by 10x
Ka = (H+)(In-)(HIn)
H+ = Ka x (HIn) = Ka x 10(In-)
H+ = 10Ka
-lgH+ = -lg 10 - lgKa
pH = -1 + pKa
pH = -1 + 4.5 pH = 3.5
[HIn] =10[In-] 1
[HIn] = 1[In-] 10[In-] > [HIn] by 10x
Ka = (H+)(In-)(HIn)
H+ = Ka x (HIn) = Ka x 1/10(In-)
H+ = Ka /10-lgH+ = - lgKa - lg10-1
pH = pKa + 1pH = 4.5 + 1 = 5.5pH = 5.5
[HIn] = 1[In-] 10
[HIn] = 1[In-] 1
pH ≤ 3.5, eye detect RED pH ≥ 5.5, eye detect BLUE
[Hin] > [In-] by 10x Conc [Hin] < [In-] by 10x
[HIn] = 1[In-] 1[HIn] = [In-]
Titration bet strong acid with strong baseHCI + NaOH→ NaCI + H2O
Titration curves Strong Acid with Strong Base
NaOHM = 0.1MV = 0 ml
7
HCI + NaOH → NaCI + H2OM = 0.1M M = 0.1MV = 25ml V = 25ml
2.7
11.3
• Rapid jump in pH (2.7 – 11.3)• Rapid change at equivalence pt (25ml base)• Equivalence pt → amt acid = amt base• End pt → indicator change colour• Equvalence pt must coincide with end pt at 25ml• pH at equivalence pt = 7• Neutral salt, NaCI - neutral
1
HCIM = 0.1MV = 25ml
pH = 1
HCIM = 0.1MV = 1ml left
NaOHM = 0.1MV = 24 ml add
pH = 2.7
NaOHM = 0.1MV = 25 ml add
HCIM = 0.1MV = 0ml left
pH = 7
NaOHM = 0.1MV = 26 ml
pH = 11.3
NaOHV = 1ml left
Mole ratio – 1: 1NaOH
M = 0.1MV = 25ml
HCIM = 0.1MV = 25ml
Indicator pKa pH range
ColourAcid
Methyl orange 3.46 3.2- 4.4 RED
Bromophenol Blue 4.10 3.0- 4.6 Yellow
Bromocresol Green 4.90 3.8- 5.4 Yellow
Methyl Red 5.00 4.8- 6.0 Red
Bromothymol Blue 7.30 6.0- 7.6 Yellow
Phenol Red 8.00 6.6- 8.0 Yellow
Phenolphthalein 9.50 8.2- 10.0 Colourless
Indicator pKa pH range
ColourBase
Methyl orange 3.46 3.2- 4.4 Yellow
Bromophenol Blue 4.10 3.0- 4.6 Blue
Bromocresol Green 4.90 3.8- 5.4 Blue
Methyl Red 5.00 4.8- 6.0 Yellow
Bromothymol Blue 7.30 6.0- 7.6 Blue
Phenol Red 8.00 6.6- 8.0 Red
Phenolphthalein 9.50 8.2- 10.0 Pink
25 ml base add:• Equivalence pt reach• Indicator change colour
Acidic mediumBasic medium
V = 25ml
Titration bet strong acid with strong baseHCI + NaOH→ NaCI + H2O
Titration curves Strong Acid with Strong Base
11.3
2.7
NaOHM = 0.1MV = 25ml
HCIM = 0.1MV = 25ml
1
7
V = 25ml
Indicator pKa pH range ColourChange
Acid
ColourChange
Base
Methyl orange 3.46 3.2- 4.4 RED Yellow
Bromophenol Blue 4.10 3.0- 4.6 Yellow Blue
Bromocresol Green 4.90 3.8- 5.4 Yellow Blue
Methyl Red 5.00 4.8- 6.0 Red Yellow
Bromothymol Blue 7.30 6.0- 7.6 Yellow Blue
Phenol Red 8.00 6.6- 8.0 Yellow Red
Phenolphthalein 9.50 8.2- 10.0 Colourless PinkEquivalence pt occurs when 25ml base added• pH rise sharply (2.7 – 11.3)• Indicator MUST change colour at equivalence pt• Indicator with pKa falls in pH range (2.7 – 11.3) suitable• Equivalence Pt and End Pt coincide when 25ml base add. Indicator change colour at equivalent pt (25ml) when pH jumps from 2.7 – 11.3
• pKa indicator within (2.7 – 11.3)
Indicator pKa pH range Acid Base
Methyl orange 3.46 3.2- 4.4 RED Yellow
Indicator pKa pH range Acid Base
Phenolphthalein 9.5 8.2 - 10 Colourless PINK
Methyl Orange change colour at 3.2 – 4.4 at equivalence pt, 25ml.
Phenolphthalein change colour at 8.2- 10at equivalence pt, 25ml
Methyl Orange can be used as Indicator Phenolphthalein can be used as Indicator
V = 25ml V = 25ml
11.3 11.3
2.7 2.7
1 1
Titration bet strong acid with strong baseCH3COOH + NaOH→ CH3COONa + H2O
Titration curves Weak Acid with Strong Base
NaOHM = 0.1MV = 0 ml
9
CH3COOH + NaOH → CH3COONa + H2OM = 0.1M M = 0.1MV = 25ml V = 25ml
6.11
11.3
• Rapid jump in pH (6.11 – 11.3)• Rapid change at equivalence pt (25ml base)• Equivalence pt → amt acid = amt base• End point → indicator changes colour• Equvalence pt must coincide with end pt at 25ml• pH at equivalence pt = 9• Basic salt, CH3COONa - basic
2.87
pH = 2.87
NaOHM = 0.1MV = 24 ml add
pH = 6.11
NaOHM = 0.1MV = 25ml add
pH = 9
NaOHM = 0.1MV = 26ml
pH = 11.3
NaOHV = 1ml left
Mole ratio – 1: 1NaOH
M = 0.1MV = 25ml
Indicator pKa pH range
ColourAcid
Methyl orange 3.46 3.2- 4.4 RED
Bromophenol Blue 4.10 3.0- 4.6 Yellow
Bromocresol Green 4.90 3.8- 5.4 Yellow
Methyl Red 5.00 4.8- 6.0 Red
Bromothymol Blue 7.30 6.0- 7.6 Yellow
Phenol Red 8.00 6.6- 8.0 Yellow
Phenolphthalein 9.50 8.2- 10.0 Colourless
Indicator pKa pH range
ColourBase
Methyl orange 3.46 3.2- 4.4 Yellow
Bromophenol Blue 4.10 3.0- 4.6 Blue
Bromocresol Green 4.90 3.8- 5.4 Blue
Methyl Red 5.00 4.8- 6.0 Yellow
Bromothymol Blue 7.30 6.0- 7.6 Blue
Phenol Red 8.00 6.6- 8.0 Red
Phenolphthalein 9.50 8.2- 10.0 Pink
25ml base added:• Equivalence pt reach• Indicator change colour
Acidic mediumBasic medium
CH3COOHM = 0.1MV = 25ml
CH3COOHM = 0.1MV = 1ml
CH3COOHM = 0.1MV = 0ml left
CH3COOHM = 0.1MV = 25ml
V = 25ml
Titration bet weak acid with strong baseCH3COOH + NaOH → CH3COONa + H2O
6.11
11.3NaOH
M = 0.1MV = 25ml
CH3COOHM = 0.1MV = 25ml
2.87
V = 25ml
Titration curve Weak Acid with Strong Base
Equivalence pt occur when 25ml base added• pH rise sharply (6.11 – 11.3)• Indicator MUST change colour at equivalence pt• Indicator with pKa falls in pH range (6.11 – 11.3) suitable• Equivalence pt and End pt coincide when 25ml base added.
Indicator pKa pH range ColourChange
Acid
ColourChange
Base
Methyl orange 3.46 3.2- 4.4 RED Yellow
Bromophenol Blue 4.10 3.0- 4.6 Yellow Blue
Bromocresol Green 4.90 3.8- 5.4 Yellow Blue
Methyl Red 5.00 4.8- 6.0 Red Yellow
Bromothymol Blue 7.30 6.0- 7.6 Yellow Blue
Phenol Red 8.00 6.6- 8.0 Yellow Red
Phenolphthalein 9.50 8.2- 10.0 Colourless Pink
Indicator change colour at equivalent pt (25ml) when pH jumps from 6.11 – 11.3• pKa indicator within (6.11 – 11.3)
Methyl Orange cannot be used as Indicator
6.11
11.3
2.87
V = 25ml
Methyl Orange change colour at 3.2 – 4.4 before equivalence pt, 25ml.
Indicator pKa pH range Acid Base
Methyl orange 3.46 3.2- 4.4 RED Yellow
Phenollphthalein can be used as Indicator
11.3
6.112.87
V = 25ml
Indicator pKa pH range Acid Base
Phenolphthalein 9.5 8.2 - 10 Colourless PINK
Phenolphthalein change colour at 8.2- 10at equivalence pt, 25ml
Titration curves Strong Acid with Weak Base
NH4OHM = 0.1MV = 0 ml
5.3
HCI + NH4OH → NH4CI + H2OM = 0.1M M = 0.1MV = 25ml V = 25ml
2.7
7.8
• Rapid jump in pH (2.7 – 7.8)• Rapid change at equivalence pt (25ml base)• Equivalence point → amt acid = amt base• End pt → indicator change colour• Equvalence pt must coincide with end pt at 25ml• pH at equivalence pt = 5.3• Acidic salt, NH4CI – acidic
1
HCIM = 0.1MV = 25ml
pH = 1
HCIM = 0.1MV = 1ml left
NH4OHM = 0.1MV = 24 ml add
pH = 2.7
NH4OHM = 0.1MV = 25ml add
HCIM = 0.1MV = 0ml left
pH = 5.3
NH4OHM = 0.1MV = 26ml
pH = 7.8
NaOHV = 1ml left
Mole ratio – 1: 1
HCIM = 0.1MV = 25ml
Indicator pKa pH range
ColourAcid
Methyl orange 3.46 3.2- 4.4 RED
Bromophenol Blue 4.10 3.0- 4.6 Yellow
Bromocresol Green 4.90 3.8- 5.4 Yellow
Methyl Red 5.00 4.8- 6.0 Red
Bromothymol Blue 7.30 6.0- 7.6 Yellow
Phenol Red 8.00 6.6- 8.0 Yellow
Phenolphthalein 9.50 8.2- 10.0 Colourless
Indicator pKa pH range
ColourBase
Methyl orange 3.46 3.2- 4.4 Yellow
Bromophenol Blue 4.10 3.0- 4.6 Blue
Bromocresol Green 4.90 3.8- 5.4 Blue
Methyl Red 5.00 4.8- 6.0 Yellow
Bromothymol Blue 7.30 6.0- 7.6 Blue
Phenol Red 8.00 6.6- 8.0 Red
Phenolphthalein 9.50 8.2- 10.0 Pink
25ml base added:• Equivalence pt reach• Indicator change colour
Acidic mediumBasic medium
Titration bet strong acid with weak baseHCI + NH4OH → NH4CI + H2O
NH4OHM = 0.1MV = 25ml
V = 25ml
V = 25ml
Equivalence pt occurs when 25ml base added• pH rise sharply (2.7 – 7.8)• Indicator MUST change colour at equivalence pt• Indicator with pKa falls in pH range (2.7 – 7.8) suitable• Equivalence Pt and End pt coincide when 25ml base added
Indicator pKa pH range ColourChange
Acid
ColourChange
Base
Methyl orange 3.46 3.2- 4.4 RED Yellow
Bromophenol Blue 4.10 3.0- 4.6 Yellow Blue
Bromocresol Green 4.90 3.8- 5.4 Yellow Blue
Methyl Red 5.00 4.8- 6.0 Red Yellow
Bromothymol Blue 7.30 6.0- 7.6 Yellow Blue
Phenol Red 8.00 6.6- 8.0 Yellow Red
Phenolphthalein 9.50 8.2- 10.0 Colourless Pink
Indicator change colour at equivalent pt (25ml ) when pH jumps from (2.7 – 7.8)• pKa of indicator within (2.7 – 7.8)
Titration bet strong acid with weak baseHCI + NH4OH → NH4CI + H2O
Titration curves Strong Acid with Weak Base
NH4OHM = 0.1MV = 25ml
HCIM = 0.1MV = 25ml
2.7
7.8
5.3
1
Indicator pKa pH range Acid Base
Methyl orange 3.46 3.2- 4.4 RED Yellow
Indicator pKa pH range Acid Base
Phenolphthalein 9.5 8.2 - 10 Colourless PINK
Phenolphthalein cannot be used as Indicator
7.8
2.7
V = 25ml 1
Phenolphthalein change colour at 8.2- 10after equivalence pt, 25ml .
Methyl Orange can be used as Indicator
7.8
2.7
V = 25ml
Methyl Orange change colour at 3.2 – 4.4 at equivalence pt, 25ml.
Titration curves Weak Acid with Weak Base
NH4OHM = 0.1MV = 0 ml
7
CH3COOH + NH4OH → CH3COONH4 + H2OM = 0.1M M = 0.1MV = 25ml V = 25ml
6.11
7.8
• No sharp rise in pH at equivalence pt (25ml base)• Equivalence pt → amt acid = amt base• End point → indicator changes colour• Equvalence pt must coincide with end pt at 25ml• pH at equivalence pt = 7• Neutral salt, CH3COONH4 – neutral
2.87
pH = 2.87
CH3COOHM = 0.1MV = 1ml left
NH4OHM = 0.1MV = 24 ml add
pH = 6.11
NH4OHM = 0.1MV = 25ml add
CH3COOHM = 0.1M
V = 0ml left
pH = 7
NH4OHM = 0.1MV = 26ml
pH = 7.8
NH4OHV = 1ml left
Mole ratio – 1: 1
Indicator pKa pH range
ColourAcid
Methyl orange 3.46 3.2- 4.4 RED
Bromophenol Blue 4.10 3.0- 4.6 Yellow
Bromocresol Green 4.90 3.8- 5.4 Yellow
Methyl Red 5.00 4.8- 6.0 Red
Bromothymol Blue 7.30 6.0- 7.6 Yellow
Phenol Red 8.00 6.6- 8.0 Yellow
Phenolphthalein 9.50 8.2- 10.0 Colourless
Indicator pKa pH range
ColourBase
Methyl orange 3.46 3.2- 4.4 Yellow
Bromophenol Blue 4.10 3.0- 4.6 Blue
Bromocresol Green 4.90 3.8- 5.4 Blue
Methyl Red 5.00 4.8- 6.0 Yellow
Bromothymol Blue 7.30 6.0- 7.6 Blue
Phenol Red 8.00 6.6- 8.0 Red
Phenolphthalein 9.50 8.2- 10.0 Pink
25ml base added:• Equivalence pt reach• Indicator change colour
Acidic mediumBasic medium
NH4OHM = 0.1MV = 25ml
Titration bet weak base with weak acidCH3COOH + NH4OH → CH3COONH4 + H2O
CH3COOHM = 0.1MV = 25ml
CH3COOHM = 0.1MV = 25ml
V = 25ml
V = 25ml
Equivalence pt occurs when 25ml base added• No sharp rise in pH• Indicator MUST change colour at equivalence pt• No Indicator suitable
Indicator pKa pH range ColourChange
Acid
ColourChange
Base
Methyl orange 3.46 3.2- 4.4 RED Yellow
Bromophenol Blue 4.10 3.0- 4.6 Yellow Blue
Bromocresol Green 4.90 3.8- 5.4 Yellow Blue
Methyl Red 5.00 4.8- 6.0 Red Yellow
Bromothymol Blue 7.30 6.0- 7.6 Yellow Blue
Phenol Red 8.00 6.6- 8.0 Yellow Red
Phenolphthalein 9.50 8.2- 10.0 Colourless Pink
• No indicators are suitable as no sharp rise in pH
NH4OHM = 0.1MV = 25ml
6.11
7.8
7
2.87
Titration curves Weak Acid with Weak Base
Titration bet weak base with weak acidCH3COOH + NH4OH → CH3COONH4 + H2O
CH3COOHM = 0.1MV = 25ml
Phenolphthalein cannot be used as Indicator
Indicator pKa pH range Acid Base
Phenolphthalein 9.5 8.2 - 10 Colourless PINK
Phenolphthalein change colour at 8.2- 10after equivalence pt, 25ml .
Indicator pKa pH range Acid Base
Methyl orange 3.46 3.2- 4.4 RED Yellow
Methyl Orange change colour at 3.2 – 4.4 before equivalence pt, 25ml.
Methyl Orange cannot be used as Indicator
6.11 6.11
7 7
7.8 7.8
V = 25ml V = 25ml
2.87 2.87
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+
NaOHNaCI
No hydrolysis Neutral salt 7
Strong acid+
Weak base
HCI+
NH3
NH4CICation
hydrolysisAcidic salt < 7
Weak acid+
Strong base
CH3COOH+
NaOHCH3COONa
Anionhydrolysis
Basic salt > 7
Weak acid+
Weak base
CH3COOH+
NH3
CH3COONH4
Anion/Cationhydrolysis
Depends ?
Click here on acidic buffer simulation
Click here buffer simulation
Salts
Weak base Strong acid
NH4OH < HCI
↓
Acidic Salt
NH4+ - Conjugate acid
NH4+ - Cation hydrolysis
NH4+ + H2O ↔ H3O
+ + NH3
Acid (proton donor)
pH < 7
Strong base Strong acidNaOH = HCI
↓
Neutral Salt
NaCI – Dissolves in water
NaCI – No water hydrolysis
pH = 7
Strong base Weak acidNaOH > CH3COOH
↓
Basic Salt
CH3COO- - Conjugate base
CH3COO- - Anion hydrolysis
CH3COO- + H2O ↔ CH3COOH + OH-
Base (proton acceptor)
pH > 7
Acidic Salt Basic SaltNeutral Salt
Strong
Acid
(HCI)
Strong
Base
(NaOH)
NaOH + HCI → NaCI + H2O
Na+ CI-
Strong
Acid
(HCI)
Weak
Base
(NH4OH)
CI-NH4+
NH4OH + HCI → NH4CI + H2O
Strong
Base
(NaOH)
Weak
Acid
(CH3COOH)
Na+ CH3COO-
NaOH + CH3COOH → CH3COONa + H2O
=
Salt Produced Examples Nature of salt
Strong acid + Strong base NaCI, Na2SO4, KNO3 Neutral (No hydrolysis)
Strong Acid + Weak base NH4CI, (NH4)2SO4, NH4NO3 Acidic (Cation Hydrolysis)
Weak Acid + Strong Base CH3COONa, Na2CO3 , Na3PO4 Basic (Anion Hydrolysis)
Weak Acid + Weak Base CH3COONH4, (NH4)3PO4 pH depends on Ka and Kb
Ka > Kb = acidicKb > Ka = basic
Water hydrolysis
Acid + Base → Salt + Water (Neutralization)
Neutralization
Salt Hydrolysis
Water hydrolysis – chemical rxn involving water
producing H+ and OH- ions
Neutralization bet Strong Acid + Weak Base
Strong
Acid
(HCI)
Weak
Base
(NH4OH)
Acidic Salt
NH4OH + HCI → NH4CI + H2O
NH4+ CI-
Weak base Strong acid
NH4OH < HCI
↓Acidic Salt
NH4+ - Conjugate acid
NH4+ - Cation hydrolysis
NH4+ + H2O ↔H3O
+ + NH3
Acid (proton donor)pH < 7
Salt Produced
Examples Nature of salt
Strong Acid + Weak base
NH4CI, (NH4)2SONH4NO3
Acidic
Acidic Salt
Salts of Transition Metal ions
Transition metal ions:• SIZE and CHARGE of cation• High charge density – Ni2+, Cu2+,Fe3+, Al3+
• Small size ion – Ni2+, Cu2+, Fe3+, Al3+
[Fe(H2O)6]3+CI3
Fe
[AI(H2O)6]3+CI3
AI
• 6 H2O attract to Fe3+ ion• Lone pair on Oxygen act as ligand• Ligand attract to Fe3+
•Form dative bond
• 6 H2O attract to AI3+ ion• Lone pair on Oxygen act as ligand• Ligand attract to AI3+
•Form dative bond
Polarise water - water hydrolysis produce H+ ions
[Fe(H2O)6]3+ → (H2O)5Fe3+ ← :O―H+ → [(H2O)5FeOH]2+ + H+
|H Water hydrolysis
Hydrogen ion produced
NH4OH + HCI → NH4CI + H2ONH4OH + H2SO4 → NH4SO4 + H2ONH4OH + HNO3 → NH4NO3 + H2O
Acidic salt
CH3COO- + H2O → CH3 COOH + OH-
Salt Hydrolysis
Neutralization Reaction Salt Salt hydrolysis Type salt pH salt
Strong acid+
Strong base
HCI+
NaOHNaCI
No hydrolysis Neutral salt 7
Strong acid+
Weak base
HCI+
NH3
NH4CICation
hydrolysisAcidic salt < 7
Weak acid+
Strong base
CH3COOH+
NaOHCH3COONa
Anionhydrolysis
Basic salt > 7
Weak acid+
Weak base
CH3COOH+
NH3
CH3COONH4
Anion/Cationhydrolysis
Depends ?
Weak acid and Weak base
CH3COOH + NH3 → CH3COONH4
Acidicity depend on Ka and Kb
Ka > Kb – Acidic – H+ ions producedKb < Ka – Basic – OH- ions producedKa = Kb – Neutral – hydrolyzed same extent.
CH3COONH4 → CH3COO- + NH4+
NH4+ + H2O → NH3 + H3O
+
salt
anion cation
OH- - Basic H3O+ - AcidicKb Ka
Ka = Kb
NEUTRAL
NH3 + HF → NH4F
salt
NH4F → NH4+ + F-
NH4+ + H2O → NH3 + H3O
+ F- + H2O → HF + OH-
cation anion
KaH3O
+ - Acidic KbOH- - Basic
Acidicity depend on Ka and Kb
Ka > Kb – Acidic – H+ ions producedKb < Ka – Basic – OH- ions producedKa = Kb – Neutral – hydrolyzed same extent.
Kb > Ka
BASIC
Weak acid
+
Weak base
Concept Map
Strong acidStrong base
Titration Acid Base
Strong acidWeak base
Weak acidStrong base
Weak acidWeak base
Neutralization Titration curve
Base
Acid Indicator2.7
11.3
7.8
2.7
11.3
6.11
7.8
6.11
Adding base to acid
End point
pH range at equivalent pt
Equivalent ptStoichiometric pt
Point of inflection
Titration bet weak acid with strong baseCH3COOH + NaOH → CH3COONa + H2O
pH buffer region
weak acid and salt
6.11
11.3
9
• Amt acid = Amt base• Vol at equivalence pt = 25ml
25ml12.5ml
Half Equivalent pt
• Amt acid = Amt salt• Vol is = 12.5ml• Buffer region form
Indicator change
colour
Titration bet strong acid with weak baseHCI + NH4OH → NH4CI + H2O
25ml
Equivalent ptStoichiometric pt
• Amt acid = Amt base• Vol at equivalence pt = 25ml
pH = pKa6.3
2.7
7.8
pH buffer region
weak base and salt
Buffer region
50ml
pOH = pKb
• Amt base = Amt salt• Vol is = 50 ml• Buffer region form
Bromocresol green has pH of 3.8 – 5.4 and changes colour from yellow to blue as pH increaseA. Which type acid/base titration is suitable to be used
Titration for strong acid/strong base or strong acid/weak base
B. Suggest value for pKa indicator.
pKa indicator corresponds to halfway through its colour-change range. pKa = 4.6
C. What colour at pH 3.6?
pH = 3.6 - yellow
IB Questions
1
2
Which of following statement always correct ?A. Mid point indicator colour change is pH =7B. pH range greater for indicator with high pKa valuesC. Colour red indicate acidicD. pKa value indicator within its pH range
3.8 5.4
4.6
pH range – change colour over a range of pH
HIn ↔ H+ + In-
(yellow) (blue)
3.8 5.4yellow blue
yellow/blue mix - green
Titration curve bet weak acid with strong base. Indicate on the graph,a) Equivalent pt, b) pH at equivalent pt, c) suitable indicator use d) pH range for indicator
NaOHM = 0.1MV = 25ml
CH3COOHM = 0.1MV = 25ml
3
6.11
11.3
25 Vol base added
9
a) Equivalent pt – 25 ml
b) pH at equivalent pt – 9
c) Suitable indicator – phenolphthalein, - change colour at equivalent pt
d) pH range indicator – 8.2 - 10
Indicator pH range
Acid Base
Phenolphthalein 8.2 - 10 Colourless PINK
Click here on universal indicatorClick here on acid base indicator
Simulation and Animation on Buffer and Titrations
Click here videos from Khan Academy
Click here acidic buffer animationClick here salt hydrolysis animationClick here titration simulation
Click here titration animation Click here titration animation
Click here on universal indicator
Acknowledgements
Thanks to source of pictures and video used in this presentation
Thanks to Creative Commons for excellent contribution on licenseshttp://creativecommons.org/licenses/
Prepared by Lawrence Kok
Check out more video tutorials from my site and hope you enjoy this tutorialhttp://lawrencekok.blogspot.com