8.116

SECTION 8

8.5 INDICATORS

TABLE 8.23

Indicators for Aqueous Acid-Base Titrations

This table lists some selected indicators. The pH range or transition interval given in the third column may vary

appreciably from one observer to another, and, in addition, it is affected by ionic strength, temperature, and

illumination; consequently only approximate values can be given. They should be considered to refer to solutions

having low ionic strengths and a temperature of about 25

C. In the fourth column the

p

K

a ( log K a ) of the

indicator as determined spectrophotometrically is listed. In the fifth column the wavelength of maximum ab-

sorption is given first for the acidic and then for the basic form of the indicator, and the same order is followed

in giving the colors in the sixth column. The abbreviations used to describe the colors of the two forms of the

indicator are as follows:

B, blue

G, green

V, violet

P, purple

Y, yellow

R, red

O, orange

O-Br, orange-brown

C, colorless

pH

Color

Indicator

Chemical name

range

p K a

max

, nm

change

Cresol red

o -Cresolsulfonephthalein

0.2

– 1.8

R-Y

(acid range)

Cresol purple

m

-Cresolsulfonephthalein

1.2

– 2.8

1.51

533,

—

R-Y

(acid range)

Thymol blue

Thymolsulfonephthalein

1.2

– 2.8

1.65

544,

430

R-Y

(acid range)

Tropeolin OO

Diphenylamino-

p -benzene

1.3– 3.2

2.0

527,

—

R-Y

sodium sulfonate

2,6-Dinitrophenol

2,6-Dinitrophenol

2.4–

4.0

3.69

C-Y

2,4-Dinitrophenol

2,4-Dinitrophenol

2.5–

4.3

3.90

C-Y

Methyl yellow

Dimethylaminoazobenzene

2.9–

4.0

3.3

508, —

R-Y

Methyl orange

Dimethylaminoazobenzene

3.1– 4.4

3.40

522, 464

R-O

sodium sulfonate

Bromophenol blue

Tetrabromophenolsulfone-

3.0– 4.6

3.85

436, 592

Y-BV

phthalein

Bromocresol green

Tetrabromo-

m

-cresol-

4.0– 5.6

4.68

444, 617

Y-B

sulfonephthalein

Methyl red

o -Carboxybenzeneazo-

4.4– 6.2

4.95

530, 427

R-Y

dimethylaniline

Chlorophenol red

Dichlorophenolsulfone-

5.4– 6.8

6.0

— , 573

Y-R

phthalein

Bromocresol purple

Dibromo-

o -cresolsulfone-

5.2– 6.8

6.3

433, 591

Y-P

phthalein

Bromophenol red

Dibromophenolsulfone-

5.2– 6.8

— , 574

Y-R

phthalein

p -Nitrophenol

p -Nitrophenol

5.3– 7.6

7.15

320, 405

C-

Y

Bromothymol blue

Dibromothymolsulfone-

6.2– 7.6

7.1

433, 617

Y-B

phthalein

Neutral red

Aminodimethylaminotolu-

6.8– 8.0

7.4

R-Y

phenazonium chloride

Phenol red

Phenolsulfonephthalein

6.4– 8.0

7.9

433, 558

Y-R

m -Nitrophenol

m

-Nitrophenol

6.4– 8.8

8.3

— , 570

C-

Y

ELECTROLYTES, EMF, AND CHEMICAL EQUILIBRIUM

8.117

TABLE 8.23

Indicators for Aqueous Acid-Base Titrations (

Continued

)

pH

Color

Indicator

Chemical name

range

p K a

max

, nm

change

Cresol red

o -Cresolsulfonephthalein

7.2

– 8.8

8.2

434,

572

Y-R

m -Cresol purple

m

-Cresolsulfonephthalein

7.6

– 9.2

8.32

— , 580

Y-P

Thymol blue

Thymolsulfonephthalein

8.0– 9.6

8.9

430, 596

Y-B

Phenolphthalein

Phenolphthalein

8.0– 10.0

9.4

— , 553

C-R

-Naphtholbenzein

-Naphtholbenzein

9.0– 11.0

Y

-B

Thymolphthalein

Thymolphthalein

9.4– 10.6

10.0

— , 598

C-B

Alizarin Yellow R

5-(

p -Nitrophenylazo)-

10.0– 12.0

11.16

Y-V

salicyclic acid, Na salt

Tropeolin O

p -Sulfobenzenazo-

11.0– 13.0

Y-O-Br

resorcinol

Nitramine

2,4,6-Trinitrophenyl-

10.8– 13.0

C-O-Br

methylnitroamine

TABLE 8.24 Mixed Indicators

Mixed indicators give sharp color changes and are especially useful in titrating to a given titration exponent (p

I).

The information given in this table is from the two-volume work

Volumetric Analysis

by Kolthoff and Stenger,

published by Interscience Publishers, Inc., New York, 1942 and 1947, and reproduced with their permission.

Color

Composition of Indicator Solution

p

I

Acid

Alkaline

Notes

1

part 0.1%

methyl yellow in alc.

*

Blue-violet

Green

Still

green at pH 3.4, blue-violet at 3.2†

1

part 0.1%

methylene blue in alc.

3.25

1

part 0.14% xylene cyanol FF in alc.

*

1

part 0.1%

methyl orange in aq.

3.8

Violet

Green

Color is gray at pH 3.8

1

part 0.1%

methyl orange in aq.

*

1

part 0.25% indigo carmine in aq.

4.1

Violet

Green

Good indicator, especially in artificial light

1

part 0.1%

methyl orange in aq.

1

part 0.1%

aniline blue in aq.

4.3

Violet

Green

1

part 0.1%

bromcresol green sodium salt in aq.

Orange

Blue-green

Yellow at pH 3.5, greenish yellow at 4.0, weakly green at 4.3

1

part 0.02% methyl orange in aq.

4.3

3 parts 0.1%

bromcresol green in alc.

Wine-red

Green

Very sharp color change†

1

part 0.2% methyl red in alc.

5.1

1

part 0.2% methyl red in alc.

*

Red-violet

Green

Color is red-violet at pH 5.2, a dirty blue at 5.4, and a dirty green at 5.6

1

part 0.1%

methylene blue in alc.

5.4

1

part 0.1%

chlorphenol red sodium salt in aq.

1

part 0.1%

aniline blue in water

5.8

Green

Violet

Pale violet at pH 5.8

1

part 0.1%

bromcresol green sodium salt in aq.

Yellow-green

Blue-violet

Blue-green at pH 5.4, blue at 5.8, blue with a touch of violet at 6.0,

1

part 0.1%

chlorphenol red sodium salt in aq.

6.1

blue-violet at 6.2

1

part 0.1%

bromcresol purple sodium salt in aq.

Yellow

Violet-blue

Yellow-violet at pH 6.2, violet at 6.6, blue-violet at 6.8

1

part 0.1%

bromthymol blue sodium salt in aq.

6.7

2 parts 0.1% bromthymol blue sodium salt in aq.

Violet

Blue

1

part 0.1%

azolitmin in aq.

6.9

118.8

8.120

SECTION 8

TABLE 8.25

Fluorescent Indicators

Color Change

Indicator

Name

pH Range

Acid to Base

Solution

Benzoflavine

0.3 to 1.7

Yellow to green

1

3,6-Dihydroxyphthalimide

0

to 2.4

Blue to green

1

6.0 to 8.0

Green to yellow/green

Eosin (tetrabromofluorescein)

0 to 3.0

Non-fl to green

4, 1%

4-Ethoxyacridone

1.2 to 3.2

Green to blue

1

3,6-Tetramethyldiaminoxanthone

1.2 to 3.4

Green to blue

1

Esculin

1.5 to 2.0

Weak blue to strong blue

Anthranilic acid

1.5 to 3.0

Non-fl to light blue

2 (50% ethanol)

4.5 to 6.0

Light blue to dark blue

12.5 to 14

Dark blue to non-fl

3-Amino-1-naphthoic acid

1.5 to 3.0

Non-fl to green

2 (as sulfate

4.0 to 6.0

Green to blue

in 50% ethanol)

11.6 to 13.0

Blue to non-fl

1-Naphthylamino-6-sulfonamide

1.9 to 3.9

Non-fl to green

3

(also the 1-, 7-)

9.6 to 13.0

Green to non-fl

2-Naphthylamino-6-sulfonamide

1.9 to 3.9

Non-fl to dark blue

3

(also the 2-, 8-)

9.6 to 13.0 Dark blue to non-fl

1-Naphthylamino-5-sulfonamide

2.0 to 4.0

Non-fl to yellow/orange

3

9.5 to 13.0 Yellow/orange to non-fl

1-Naphthoic acid

2.5 to 3.5

Non-fl to blue

4

Salicylic acid

2.5 to 4.0

Non-fl to dark blue

4 (0.5%)

Phloxin BA extra

2.5 to 4.0

Non-fl to dark blue

2

(tetrachlorotetrabromofluorescein)

Erythrosin B (tetraiodofluorescein)

2.5 to 4.0

Non-fl to light green

4 (0.2%)

2-Naphthylamine

2.8 to 4.4

Non-fl to violet

1

Magdala red

3.0 to 4.0

Non-fl to purple

p -Aminophenylbenzenesulfonamide

3.0 to 4.0

Non-fl to light blue

3

2-Hydroxy-3-naphthoic acid

3.0 to 6.8

Blue to green

4 (0.1%)

Chromotropic acid

3.1 to 4.4

Non-fl to light blue

4 (5%)

1-Naphthionic acid

3 to 4

Non-fl to blue

4

10 to 12

Blue to yellow-green

1-Naphthylamine

3.4 to 4.8

Non-fl to blue

1

5-Aminosalicylic acid

3.1 to 4.4

Non-fl to light green

1 (0.2% fresh)

Quinine

3.0 to 5.0

Blue to weak violet

1 (0.1%)

9.5 to 10.0 Weak violet to non-fl

o -Methoxybenzaldehyde

3.1 to 4.4

Non-fl to green

4 (0.2%)

o -Phenylenediamine

3.1 to 4.4

Green to non-fl

5

p -Phenylenediamine

3.1 to 4.4

Non-fl to orange/yellow

5

Morin (2 ,4 ,3,5,7-pentahydroxyflavone)

3.1 to 4.4

Non-fl to green

6 (0.2%)

8 to 9.8

Green to yellow/green

Thioflavine S

3.1 to 4.4

Dark blue to light blue

6 (0.2%)

Fluorescein

4.0 to 4.5

Pink/green to green

4 (1%)

Dichlorofluorescein

4.0 to 6.6

Blue green to green

1

-Methylesculetin

4.0 to 6.2

Non-fl to blue

1

9.0 to 10.0 Blue to light green

Quininic acid

4.0 to 5.0

Yellow to blue

6 (satd)

-Naphthoquinoline

4.4 to 6.3

Blue to non-fl

3

Resorufin (7-oxyphenoxazone)

4.4 to 6.4

Yellow to orange

Indicator solutions: 1, 1% solution in ethanol; 2, 0.1% solution in ethanol; 3, 0.05% solution in 90% ethanol; 4, sodium or

potassium salt in distilled water; 5, 0.2% solution in 70% ethanol; 6, distilled water.

Reference:

G.F. Kirkbright, “Fluorescent

Indicators,”

Chap.

9 in

Indicators,

E. Bishop

(ed.), Pergamon Press, Oxford,

1972.

ELECTROLYTES,

EMF, AND CHEMICAL EQUILIBRIUM

8.121

TABLE 8.25 Fluorescent Indicators (

Continued

)

Color Change

Indicator

Name

pH Range

Acid to Base

Solution

Acridine

5.2 to 6.6

Green to violet

2

3,6-Dihydroxyxanthone

5.4 to 7.6

Non-fl to blue/violet

1

5,7-Dihydroxy-4-methylcoumarin

5.5 to 5.8

Light blue to dark blue

3,6-Dihydroxyphthalic acid dinitrile

5.8 to 8.2

Blue to green

1

1,4-Dihydroxybenzenedisulfonic acid

6 to 7

Non-fl to light blue

4 (0.1%)

Luminol

6 to 7

Non-fl to blue

2-Naphthol-6-sulfonic acid

5– 7 to 8– 9

Non-fl to blue

4

Quinoline

6.2 to 7.2

Blue to non-fl

6 (satd)

1-Naphthol-5-sulfonic acid

6.5 to 7.5

Non-fl to green

6 (satd)

Umbelliferone

6.5 to 8.0

Non-fl to blue

Magnesium-8-hydroxyquinolinate

6.5 to 7.5

Non-fl to yellow

6 (0.1% in

0.01 M HCl)

Orcinaurine

6.5 to 8.0

Non-fl to green

6 (0.03%)

Diazo brilliant yellow

6.5 to 7.5

Non-fl to blue

Coumaric acid

7.2 to 9.0

Non-fl to green

1

-Methylumbelliferone

7.0

Non-fl to blue

2 (0.3%)

Harmine

7.2 to 8.9

Blue to yellow

2-Naphthol-6,8-disulfonic acid

7.5 to 9.1

Blue to light blue

4

Salicylaldehyde semicarbazone

7.6 to 8.0

Yellow to blue

2

1-Naphthol-2-sulfonic acid

8.0 to 9.0

Dark blue to light blue

4

Salicylaldehyde acetylhydrazone

8.3

Non-fl to green/blue

2

Salicylaldehyde thiosemicarbazone

8.4

Non-fl to blue/green

2

1-Naphthol-4-sulfonic acid

8.2

Dark blue to light blue

4

Naphthol AS

8.2 to 10.3 Non-fl to yellow/green

4

2-Naphthol

8.5 to 9.5

Non-fl to blue

2

Acridine orange

8.4 to 10.4 Non-fl to yellow/green

1

Orcinsulfonephthalein

8.6 to 10.0

Non-fl to yellow

2-Naphthol-3,6-disulfonic acid

9.0 to 9.5

Dark blue to light blue

4

Ethoxyphenylnaphthostilbazonium chloride

9 to 11

Green to non-fl

1

o -Hydroxyphenylbenzothiazole

9.3

Non-fl to blue green

2

o -Hydroxyphenylbenzoxazole

9.3

Non-fl to blue/violet

2

o -Hydroxyphenylbenzimidazole

9.9

Non-fl to blue/violet

2

Coumarin

9.5 to 10.5 Non-fl to light green

6,7-Dimethoxyisoquinoline-1-carboxylic acid

9.5 to 11.0

Yellow to blue

0.1% in glycerine/

ethanol/water in

2 : 2 : 18ratio

1-Naphthylamino-4-sulfonamide

9.5 to 13.0 Dark blue to white/blue

3

TABLE 8.26 Selected List

of

Oxidation-Reduction Indicators

Reduction Potential

(30

C) in Volts at

Suitable

Color Change

Name

pH

0

pH 7

pH Range

Upon Oxidation

Bis(5-bromo-1,10-phenanthroline)

1.41*

Red to faint blue

ruthenium(II) dinitrate

Tris(5-nitro-1,10-phenanthroline)

1.25*

Red to faint blue

iron(II) sulfate

Iron(II)-2,2

,2 -tripyridine sulfate

1.25*

Pink to faint blue

Tris(4,7-diphenyl-1,10-phenanthroline)

1.13 (4.6

M

H

2 SO

4 )*

Red to faint blue

iron(II) disulfate

0.87 (1.0

M

H

2 SO

4 )*

o,m -Diphenylaminedicarboxylic acid

1.12

Colorless to blue-violet

Setopaline

1.06 (

trans

)†

Yellow to orange

p -Nitrodiphenylamine

1.06

Colorless to violet

Tris(1,10-phenanthroline)-iron(II) sulfate

1.06 (1.00

M

H 2 SO

4 )*

Red to faint blue

1.00 (3.0

M

H

2 SO

4 )*

0.89 (6.0

M

H

2 SO

4 )*

Setoglaucine O

1.01 (

trans

)†

Yellow-green to yellow-red

Xylene cyanole FF

1.00 (

trans

)†

Yellow-green to pink

Erioglaucine A

1.00 (

trans

)†

Green-yellow to bluish red

Eriogreen

0.99 (

trans

)†

Green-yellow to orange

Tris(2,2 -bipyridine)-iron(II)

0.97*

Red to faint blue

hydrochloride

2-Carboxydiphenylamine [

N

-phenyl-

0.94

Colorless to pink

anthranilic acid]

Benzidine dihydrochloride

0.92

Colorless to blue

o -Toluidine

0.87

Colorless to blue

Bis(1,10-phenanthroline)-osmium(II)

0.859 (0.1 M

H 2 SO

4 )

Green to pink

perchlorate

Diphenylamine-4-sulfonate (Na salt)

0.85

Colorless to violet