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 left More [HIn ] → red , [HIn] > [In-]

HIn ↔ H+ + In- (H+ ion ↓) - Equilibrium shift to right More [In- ] → blue, [In-] > [HIn]

Indicator pKa pH range

Colour Acid

Colour 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- 8.2 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 guide Click 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

Colour Acid

Colour 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

Indicator pKa pH range

Colour Acid

Colour Base

Methyl orange 3.46 3.2- 4.4 RED Yellow

pH 1 pH 4.4

Acid Base

Methyl Orange

Indicator pKa pH range

Colour Acid

Colour Base

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 14 pH 3.2

Equivalence Point End Point

Amt of acid = Amt base (Neutralization)

Indicator change colour

pKa – 3.46

Eye cannot detect

Eye cannot detect

HIn ↔ H+ + In-

(red) (yellow)

HIn ↔ H+ + In-

(yellow) (pink)

Indicator pKa pH range

Colour Acid

Colour Base

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

Colour Acid

Colour Base

Methyl orange 3.46 3.2- 4.4 RED Yellow

pH range

(3.2 – 4.4)

pH 1 pH 4.4 3.46

pH range – change colour over a range of pH, - always include pKa

Acid Base

Methyl Orange

Indicator pKa pH range

Colour Acid

Colour Base

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 14 pH 3.2

Equivalence Point End Point

Amt of acid = Amt base (Neutralization)

Indicator change colour

• 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

Colour Acid

Colour 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

Indicator pKa pH range

Colour Acid

Colour Base

Phenol Red 8.00 6.6- 8.2 Yellow Pink

Phenolphthalein 9.50 8.2- 10.0 Colourless Pink

Indicator Colour Acid

pKa pH range

Colour Base

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 + 1

pH = 4.5 + 1 = 5.5 pH = 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 base HCI + NaOH → NaCI + H2O

Titration curves Strong Acid with Strong Base

NaOH M = 0.1M V = 0 ml

7

HCI + NaOH → NaCI + H2O M = 0.1M M = 0.1M V = 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

HCI M = 0.1M V = 25ml

pH = 1

HCI M = 0.1M V = 1ml left

NaOH M = 0.1M V = 24 ml add

pH = 2.7

NaOH M = 0.1M V = 25 ml add

HCI M = 0.1M V = 0ml left

pH = 7

NaOH M = 0.1M V = 26 ml

pH = 11.3

NaOH V = 1ml left

Mole ratio – 1: 1 NaOH M = 0.1M V = 25ml

HCI M = 0.1M V = 25ml

Indicator

pKa pH range

Colour Acid

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

Colour Base

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 medium Basic medium

V = 25ml

Titration bet strong acid with strong base HCI + NaOH → NaCI + H2O

Titration curves Strong Acid with Strong Base

11.3

2.7

NaOH M = 0.1M V = 25ml

HCI M = 0.1M V = 25ml

1

7

V = 25ml

Indicator pKa pH range Colour Change

Acid

Colour Change

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 Equivalence 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- 10 at 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 base CH3COOH + NaOH → CH3COONa + H2O

Titration curves Weak Acid with Strong Base

NaOH M = 0.1M V = 0 ml

9

CH3COOH + NaOH → CH3COONa + H2O M = 0.1M M = 0.1M V = 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

NaOH M = 0.1M V = 24 ml add

pH = 6.11

NaOH M = 0.1M V = 25ml add

pH = 9

NaOH M = 0.1M V = 26ml

pH = 11.3

NaOH V = 1ml left

Mole ratio – 1: 1 NaOH M = 0.1M V = 25ml

Indicator

pKa pH range

Colour Acid

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

Colour Base

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 medium Basic medium

CH3COOH M = 0.1M V = 25ml

CH3COOH M = 0.1M V = 1ml

CH3COOH M = 0.1M V = 0ml left

CH3COOH M = 0.1M V = 25ml

V = 25ml

Titration bet weak acid with strong base CH3COOH + NaOH → CH3COONa + H2O

6.11

11.3 NaOH M = 0.1M V = 25ml

CH3COOH M = 0.1M V = 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 Colour Change

Acid

Colour Change

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

6.11 2.87

V = 25ml

Indicator pKa pH range Acid Base

Phenolphthalein 9.5 8.2 - 10 Colourless PINK

Phenolphthalein change colour at 8.2- 10 at equivalence pt, 25ml

Titration curves Strong Acid with Weak Base

NH4OH M = 0.1M V = 0 ml

5.3

HCI + NH4OH → NH4CI + H2O M = 0.1M M = 0.1M V = 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

HCI M = 0.1M V = 25ml

pH = 1

HCI M = 0.1M V = 1ml left

NH4OH M = 0.1M V = 24 ml add

pH = 2.7

NH4OH M = 0.1M V = 25ml add

HCI M = 0.1M V = 0ml left

pH = 5.3

NH4OH M = 0.1M V = 26ml

pH = 7.8

NaOH V = 1ml left

Mole ratio – 1: 1

HCI M = 0.1M V = 25ml

Indicator

pKa pH range

Colour Acid

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

Colour Base

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 medium Basic medium

Titration bet strong acid with weak base HCI + NH4OH → NH4CI + H2O

NH4OH M = 0.1M V = 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 Colour Change

Acid

Colour Change

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 base HCI + NH4OH → NH4CI + H2O

Titration curves Strong Acid with Weak Base

NH4OH M = 0.1M V = 25ml

HCI M = 0.1M V = 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- 10 after 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

NH4OH M = 0.1M V = 0 ml

7

CH3COOH + NH4OH → CH3COONH4 + H2O M = 0.1M M = 0.1M V = 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

CH3COOH M = 0.1M V = 1ml left

NH4OH M = 0.1M V = 24 ml add

pH = 6.11

NH4OH M = 0.1M V = 25ml add

CH3COOH M = 0.1M V = 0ml left

pH = 7

NH4OH M = 0.1M V = 26ml

pH = 7.8

NH4OH V = 1ml left

Mole ratio – 1: 1

Indicator

pKa pH range

Colour Acid

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

Colour Base

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 medium Basic medium

NH4OH M = 0.1M V = 25ml

Titration bet weak base with weak acid CH3COOH + NH4OH → CH3COONH4 + H2O

CH3COOH M = 0.1M V = 25ml

CH3COOH M = 0.1M V = 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 Colour Change

Acid

Colour Change

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

NH4OH M = 0.1M V = 25ml

6.11

7.8

7

2.87

Titration curves Weak Acid with Weak Base

Titration bet weak base with weak acid CH3COOH + NH4OH → CH3COONH4 + H2O

CH3COOH M = 0.1M V = 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- 10 after 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 +

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

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 acid NaOH = HCI ↓

Neutral Salt

NaCI – Dissolves in water

NaCI – No water hydrolysis

pH = 7

Strong base Weak acid NaOH > CH3COOH ↓

Basic Salt

CH3COO- - Conjugate base

CH3COO- - Anion hydrolysis

CH3COO- + H2O ↔ CH3COOH + OH-

Base (proton acceptor)

pH > 7

Acidic Salt Basic Salt Neutral 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 = acidic Kb > 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)2SON

H4NO3

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 + H2O NH4OH + H2SO4 → NH4SO4 + H2O NH4OH + 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 +

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

Concept Map

Strong acid Strong base

Titration Acid Base

Strong acid Weak base

Weak acid Strong base

Weak acid Weak base

Neutralization Titration curve

Base

Acid Indicator 2.7

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 pt Stoichiometric pt

Point of inflection

Titration bet weak acid with strong base CH3COOH + NaOH → CH3COONa + H2O

pH buffer region

weak acid and salt

6.11

11.3

9

• Amt acid = Amt base • Vol at equivalence pt = 25ml

25ml 12.5ml

Half Equivalent pt

• Amt acid = Amt salt • Vol is = 12.5ml • Buffer region form

Indicator change

colour

Titration bet strong acid with weak base HCI + NH4OH → NH4CI + H2O

25ml

Equivalent pt Stoichiometric pt

• Amt acid = Amt base • Vol at equivalence pt = 25ml

pH = pKa 6.3

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 increase A. 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 =7 B. pH range greater for indicator with high pKa values C. Colour red indicate acidic D. 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 5.4 yellow 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

NaOH M = 0.1M V = 25ml

CH3COOH M = 0.1M V = 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 indicator Click here on acid base indicator

Simulation and Animation on Buffer and Titrations

Click here videos from Khan Academy

Click here acidic buffer animation Click here salt hydrolysis animation Click here titration simulation

Click here titration animation Click here titration animation

Click here on universal indicator