IB Chemistry on Acid Base Indicators and Salt Hydrolysis

Acid Base Indicators

Indicators • Organic dye of weak acid/weak base with pKa/pKb value • Detect equivalence point in titration • HIn as indicator have 2 different colours in acidic/alkaline medium

HIn ↔ H+ + In-

(red) (blue)

HIn ↔ H+ + In- • (H+ ions ↑) - Equilibrium shift to left • More [HIn ] → red , [HIn] > [In-]

HIn ↔ H+ + In- (H+ ions ↓) - 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 colours red/blue will have equal conc, • Indicator have colour in bet red and blue (start to change colour)

[HIn] = [In-] Equivalence Point

Start to change colour

HIn ↔H+ + In- HIn In-

[HIn] = [In-] RED + BlUE

x log

both sides

Click here on indicator notes from chem guide

Click here on detail acid/base notes

http://www.chemguide.co.uk/physical/acidbaseeqia/indicators.html

http://wphschem.webs.com/acidsandbases.htm

• Indicators change colour at its pKa but it cannot be detected by our eyes • pH range – Indicator changes colour over a range of pH • Methyl orange, pKa is 3.46 but change colour in the range of pH (3.2-4.4) • pH range (pH = pKa ±1) seen by our eye • Indicator must only change colour at equivalence point • End point of indicator must correspond/coincide with equivalence point • Colour change must occur rapidly at equivalence point • Indicator usually change colour over a region of 2 pH units centered on pKa

Indicator change colour at its pKa

Indicator do not change colour at pH 7



Colour Acid

Colour Base






Phenol Red 8.00 6.6- 8.2 Yellow Pink

Phenolphthalein 9.50 8.2- 10.0 Colourless Pink Indicator pKa pH range

Colour

Acid

Colour Base


pH range

(3.2 – 4.4)

pH 1 pH 4.4 3.46

pH range – changes colour over a range of pH

Acid Base

Methyl Orange Indicator


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

pH range – changes colour over a range of pH

Equivalence Point End Point

Amt of acid = Amt base (Neutralization)

Indicator change colour

Indicator Colour Acid

pKa pH range

Colour Base

HIn RED 4.5 3.5 – 5.5 BLUE


pH 1 pH 3.5 4.5

pH 5.5 pH 14

HIn Indicator

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 detects it RED pH ≥ 5.5, eye detects it BLUE

Conc [Hin] > [In-] by 10x Conc [Hin] < [In-] by 10x

[HIn] = 1 [In-] 1 [HIn] = [In-]

Titration between strong acid(flask) with strong base(burette) 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 point (25ml base) • Equivalence point → amt acid = amt base • End point → indicator change colour • Equvalence point must coincide with end point at 25ml • pH at equivalence point = 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 added

pH = 2.7

NaOH M = 0.1M V = 25ml added


pH = 7

NaOH M = 0.1M V = 26ml

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

25ml base added: • Equivalence point reach • Indicator change colour

Acidic medium Basic medium

V = 25ml

Titration between strong acid(flask) with strong base(burette) HCI + NaOH → NaCI + H2O

Titration curves Strong Acid with Strong Base

11.3

2.7


HCI M = 0.1M V = 25ml

1

7

V = 25ml

Indicator pKa pH range Colour Change

Acid

Colour Change

Base







Phenolphthalein 9.50 8.2- 10.0 Colourless Pink Equivalence point occurs when 25ml base added • pH rise sharply (2.7 – 11.3) • Indicator MUST change colour at equivalence point • Indicator with pKa falls in pH range (2.7 – 11.3) suitable • Equivalence Point and End Point coincide when 25ml base added. Indicator change colour at equivalent point (25ml) when pH jumps from 2.7 – 11.3

• pKa indicator within (2.7 – 11.3)

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 point, 25ml.

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

Methyl Orange can be used as Indicator Phenollphthalein can be used as Indicator

V = 25ml

V = 25ml

11.3 11.3

2.7 2.7

1 1

Titration between strong acid(flask) with strong base(burette) 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 point (25ml base) • Equivalence point → amt acid = amt base • End point → indicator changes colour • Equvalence point must coincide with end point at 25ml • pH at equivalence point = 9 • Basic salt, CH3COONa - basic

2.87

pH = 2.87

NaOH M = 0.1M V = 24 ml added

pH = 6.11

NaOH M = 0.1M V = 25ml added

pH = 9


pH = 11.3

NaOH V = 1ml left

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

Indicator

pKa pH range

Colour Acid








Indicator

pKa pH range

Colour Base










CH3COOH M = 0.1M V = 25ml


CH3COOH M = 0.1M V = 0ml left


V = 25ml

Titration between weak acid (flask) with strong base(burette) CH3COOH + NaOH → CH3COONa + H2O

6.11

11.3 NaOH M = 0.1M V = 25ml


2.87

V = 25ml

Titration curve Weak Acid with Strong Base

Equivalence point occurs when 25ml base added • pH rise sharply (6.11 – 11.3) • Indicator MUST change colour at equivalence point • Indicator with pKa falls in pH range (6.11 – 11.3) suitable • Equivalence Point and End Point coincide when 25ml base added.


Acid

Colour Change

Base







Phenolphthalein 9.50 8.2- 10.0 Colourless Pink

Indicator change colour at equivalent point (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 point, 25ml.



Phenollphthalein can be used as Indicator

11.3

6.11 2.87

V = 25ml



Phenolphthalein change colour at 8.2- 10 at equivalence point, 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 point (25ml base) • Equivalence point → amt acid = amt base • End point → indicator change colour • Equvalence point must coincide with end point at 25ml • pH at equivalence point = 5.3 • Acidic salt, NH4CI – acidic

1

HCI M = 0.1M V = 25ml

pH = 1


NH4OH M = 0.1M V = 24 ml added

pH = 2.7

NH4OH M = 0.1M V = 25ml added


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








Indicator

pKa pH range

Colour Base










Titration between strong acid(flask) with weak base(burette) HCI + NH4OH → NH4CI + H2O

NH4OH M = 0.1M V = 25ml

V = 25ml

V = 25ml

Equivalence point occurs when 25ml base added • pH rise sharply (2.7 – 7.8) • Indicator MUST change colour at equivalence point • Indicator with pKa falls in pH range (2.7 – 7.8) suitable • Equivalence Point and End Point coincide when 25ml base added


Acid

Colour Change

Base








Indicator change colour at equivalent point (25ml ) when pH jumps from (2.7 – 7.8) • pKa of indicator within (2.7 – 7.8)

Titration between strong acid(flask) with weak base(burette) 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





Phenolphthalein cannot be used as Indicator

7.8

2.7 V = 25ml

1

Phenolphthalein change colour at 8.2- 10 after equivalence point, 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 point, 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 point (25ml base) • Equivalence point → amt acid = amt base • End point → indicator changes colour • Equvalence point must coincide with end point at 25ml • pH at equivalence point = 7 • Neutral salt, CH3COONH4 – neutral

2.87

pH = 2.87


NH4OH M = 0.1M V = 24 ml added

pH = 6.11

NH4OH M = 0.1M V = 25ml added


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








Indicator

pKa pH range

Colour Base










NH4OH M = 0.1M V = 25ml

Titration between weak base(burette) with weak acid(flask) CH3COOH + NH4OH → CH3COONH4 + H2O



V = 25ml

V = 25ml

Equivalence point occurs when 25ml base added • No sharp rise in pH • Indicator MUST change colour at equivalence point • No Indicator suitable


Acid

Colour Change

Base








• 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 between weak base(burette) with weak acid(flask) CH3COOH + NH4OH → CH3COONH4 + H2O


Phenolphthalein cannot be used as Indicator



Phenolphthalein change colour at 8.2- 10 after equivalence point, 25ml .



Methyl Orange change colour at 3.2 – 4.4 before equivalence point, 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

Salt Hydrolysis

Acid + Base → Salt + Water (Neutralization) Salt produced can be • Neutral, pH 7, No hydrolysis • Acidic, pH < 7, Cation hydrolysis • Basic, pH > 7, Anionic hydrolysis Water hydrolysis – chemical reaction involving water in producing H+ and OH- ions

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

Neutralization bet Strong Acid + Weak Base

Strong

Acid

(HCI)

Weak

Base

(NH4OH)

Acidic Salt


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)2SO4,

NH4NO3

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+

http://fineartamerica.com/featured/transition-metal-ion-colours-martyn-f-chillmaid.html

[Fe(H2O)6]3+CI3

Fe

[AI(H2O)6]3+CI3

AI

• 6 H2O attract to Fe3+ ion

• Lone pair on Oxygen act as a ligand • Ligand attract to Fe3+

• Form dative bond

• 6 H2O attract to AI3+ ion

• Lone pair on Oxygen act as a ligand • Ligand attract to AI3+

• Form dative bond

Polarise water/water hydrolysis to produce H+ ions

[Fe(H2O)6]3+ → (H2O)5Fe3+ ← :O―H+ → [(H2O)5FeOH]2+ + H+

|

H Water hydrolysis

Hydrogen ion produced


NH4OH + H2SO4 → NH4SO4+ H2O NH4OH + HNO3 → NH4NO3 + H2O

Acidic salt

Click here on universal indicator Click here on acid base indicator

Simulation and Animation on Buffer and Titrations

Click here for 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

http://www.youtube.com/watch?v=PdprNTwb4Ks

http://www.youtube.com/watch?v=jBfXAKuaw-c

http://www.youtube.com/watch?v=BBIGR0RAMtY&list=PL39E45DB611F4C7FE

http://www.media.pearson.com.au/schools/cw/au_sch_derry_ibchl_1/int/titrationCurve/1502.html

http://www.media.pearson.com.au/schools/cw/au_sch_derry_ibchl_1/int/titrationCurve/1502.html

http://www.youtube.com/watch?v=cZftblLcXbk

http://chem-ilp.net/labTechniques/AcidBaseIdicatorSimulation.htm

http://chem-ilp.net/labTechniques/AcidBaseIdicatorSimulation.htm

http://www.youtube.com/watch?v=yirkozUyG74

http://www.youtube.com/watch?v=JiSI9MWFbvk

http://www.youtube.com/watch?v=JiSI9MWFbvk

http://www.youtube.com/watch?v=PdprNTwb4Ks

http://www.youtube.com/watch?v=jBfXAKuaw-c

http://www.youtube.com/watch?v=cZftblLcXbk

http://www.youtube.com/watch?v=9Z5gWxxDcUQ

http://www.youtube.com/watch?v=9Z5gWxxDcUQ

IB Chemistry on Acid Base Indicators and Salt Hydrolysis

Education

Transcript of IB Chemistry on Acid Base Indicators and Salt Hydrolysis