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Complexometric, Oxidation, Redox and Adsorption Titration Indicators


The preparation of complexometric metal ion EDTA, Oxidation, Redox, and Adsorption Titration Indicators.


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EDTA Indicators
Redox Indicators
Adsorption Indicators

List of indicators by category


EDTA INDICATORS


Bromopyrogallol Red
Dibromopyrogallol sulphone phthalein (VIII)

Dissolve 0.05g of the reagent in 100ml. of 50% ethanol.
The indicator is coloured orange-yellow in strongly acid solutions,; claret red in nearly neutral solutions; and violet to blue in basic solutions.
Calcon or Solochrome Dark Bluealso called Eriochrome Blue Black R.
sodium 1-(2- hydroxy-1-naphthylazo)-2-naphthol-4-sulphonate, Colour I ndex No.202; Dissolve 0.2g of the dyestuff in 50ml. of methanol.
The colour change is from pink to pure blue.
Calmagite
1-(1-hydroxy-4-methyl-2-phenylazo)-2-naphthol-4-sulphonic acid (IX)
Can be substituted for Eriochrome Black T without change in the experimental procedures for calcium and magnesium.It has same colour change, which is clearer and sharper, and aqueous solutions of the indicator are almost stable indefinitely.
Dissolve 0.05g of calmagiite in 100ml. of water. The indicator is stable for at least 12 months when stored in a polythene bottle and in the dark.
Eriochrome Bkack T
Sodium 1-(1-hydroxy-2-naphthalyzo)-6-nitro-2-naphthol-4-sulphonate (1); also known as Solochrome Black T or WDFA or No. 2 in the Colour Index. Not recommended for titration of solutions more acidic than Ph 6.5.
Dissolve 0.2 g of the dyestuff in 15ml. of ethanolamine and add 5ml of absolute ethanol to reduce the viscosity; the reagent is stable for several months.
A 0.4% solution of the pure dye in methanol may last for about a month.
Colour change is from blue to red.
Eriochrome Red B
sodium salt of 4-(2-hydroxy-4-sulpho-1-naphthylazo)-3-methyl-1-phenyl-2-pyrazolin-5-one (IX)---a pyrazolone azo-B-naphthol dyestuff.
Dissolve 0.1g of the dyestuff in 50ml, ethanol. It is stable indefinitely.
The colour change from pink to pale yellow is almost instantaneous at about 80oC.
Fast Sulphon Black F
Sodium salt of 1-hydrovy-8-(2-hydroxynaphthylazo)-2-(solphonaphtylazo)-3,6-disulphonic acid (V)
The indicator solution is 0.5% solution in water.
Specific colour change for copper is from magenta to pale blue to bright green.
HHSNNA
See Patton and Reeder's
Murexide
This is the Ammonium salt of purpuric acid.
Suspend 0.5g of the powdered dyestuff in water, shake thoroughly and allow to settle. The saturated supernatant is used as the indicator.
The colour change is towards a blue endpoint.
Patton and Reeders indicator
2-hydroxy-1-(2-hydroxy-4-sulpho-1-naphthylazo)-3-naphthoic acid (111)
Also known by the abbreviated name HHSNNA.
The dyestuff is thoroughly mixed with 100 times its weight of sodium sulphate, and 1g of this mix is used for each titration.
Used in the direct titration of calcium, particularly in the presence of magnesium, pH range 12-14.
A sharp colour change is obtained from wine red to pure blue.
Pyrocatechol Violet
Pyrocatechol sulphone phthalein (VII); Catechol violet.

Dissolve 0.1g of the dyestuyy in 100ml.of water. This solution is stable for several weeks.
Colour change is progressive, from yellow yo blue to green.
Thymolphthalexone
Thymolphthalein complexone

3,3-bis-[n,n-(carboxymethyl)aminomethyl] thymolphthalein (X)
Prepare a 0.5% solution in ethanol.alternatively, a finely ground mixture 1:100 with AR potassium nitrate may be used.
Blue to colourless or slight pink in alkaline medium.
Variamine Blue B
4-methoxy-4-amino-diphenylamine
The indicator solution is a 1% solution of the base in water. Ferric complex with EDTA - sharp change in redox potential - colourless to violet blue complex.
Xylenol Orange
3,3-bis[NN-di-(carboxymethyl)-aminomethyl]-o-cresolsulphonephthalein (VI)
Dissolve 0.5g of xylenol orange indicator in 100ml of water. The solution is stable indeffinitely.
Acid solutions are coloured lemon yellow and those of the metal complexes intensely red.


REDOX INDICATORS


Amido black 10 B
dissolve 0.2 g in 100 ml of water
color change = yellowish-brown to blue
2.2'Bipyridin (iron(II) complex
dissolve 0.695 g of FeSO4.7H2O and 1.171 g of 2.2'-bipyridin in 100 ml of water
color change = pale blue to red
Brillant cresyl blue
dissolve 0.5 g in 100 ml of water or ethanol (96 %)
color change = blue to colorless
2.6-Dichlorophenolin-dophenol sodiumsalt (dihydrate)
dissolve 0.02 g in 100 ml of water
color change = blue to colorless
3.3'-Dimethylnahthidine(4.4'-Diamino-3.3-dimethyl-1.1'-binaphthaline)
dissolve 1.0 g in 100 ml of glacial acetic acid
color change = purple-red to colorless
N,N-Dimethyl-1.4-phenylenediammonium dichloride
dissolve 0.02 g in 100 ml of water
color change = dark-blue to colorless
Diphenylamine:
Dissolve 1g in 100 ml conc. H2SO4
color change = blue-violet to colorless
Diphenylamine-4-sulfonic acid barium salt
Dissolve 0.2g in 100 ml water
color change = red-violet to colorless
Diphenylamine-p-sulphonic acid (Na salt):
Dissolve 0.2g in 100 ml water.
Diphenylbenzidine:
Dissolve 1g in 100 ml conc.H2SO4
color change = violet to colorless
Ferroin:
Make a 0.025M in water.
color change = blue to orange-red
Indigo carmine (Indigo disulfonate disodium salt)
Dissolve 0.5g in 100 ml water
color change = blue to yellowish
N-Methlydiphenylamine-p-solphonic acid, (Na salt):
Dissolve 0.1g in 100 ml water.
Methylene blue
Dissolve 0.1 to 0.5g in 100 ml water
color change = blue to colorless
Neutral red
Dissolve 0.5g in 100 ml of 95% ethanol
color change = violet-red to colorless
Nile blue (sulphate)
Dissolve 0.1g in 100 ml water
color change = blue-red to colorless
1.10-Phenanthroline (monohydrate)
Dissolve 0.695 g of FeSO4 x 7H2O and 1.487 g of 1.10-Phenanthroline in 100 ml of water
color change = pale-blue to red
N-Phenylanthranilic acid:
Dissolve 0.1 g in 5 ml of 0.1M sodium hydroxide and make up to 100 ml with water.
color change = purple-red to colorless
Safranin
Dissolve 0.5g in 100 ml water
color change = blue-violet(acidic),brown (alkaline) to colorless
2.2':6.2"-Terpyridine (iron(II) complex)
Dissolve 0.232 g FeSO4 x 7H2O and 0.389 g of 2.2':6.2-terpyridine in 100 ml of water
color change = pale-blue to red
Thionine
Dissolve 0.5g in 100 ml of 95% ethanol
color change = violet to colorless
Variamine blue salt B
Dissolve 1.0 g in 100 ml of water or grind with sodium chloride or sodium sulfate anhydrous trituration
color change = blue-violet(acidic),yellow (alkaline) to colorless

ADSORPTION INDICATORS


Bromo-phenol blue:
Dissolve 0.1g in distilled water.
Dichlorofluorescein:
Dissolve 0.1g in 60 - 70 % ethanol, or
Dissolve 0.1g of dichlorofluoroceinate in 100ml water.
Diphenylamine;Dissolve 1g in 100 ml conc. sulphuric acid
Di-iododimethylfluorescein:
Dissolve 1g in 70 5 ethanol.
Diphenylcarbazide:
Dissolve 0.1g in 100 ml ethanol.
Diphenylcarbazone:
Dissolve 0.1g in 100 ml ethanol or iso-propyl alcohol.
Eosin:
Dssolve 0.1g in 100ml 70 % ethanol, or 0.1g of the sodium salt in 100 ml water.
Ferric indicator:
Use a saturated Ammonium Ferric sulphate soln. (~ 40%), add a few drops of 6M nitric acid, and use 1 ml for each titration.
Fluorescein:
Dissolve 0.2g in 100 ml 70 % alcohol, or
Dissolve 0.2g of sodium fluorocienate in 100 ml water.
Rhodamine:
Dissolve 0.05 g in 100 ml water.
Tertrazine:
Dissolve 0.5g in water and use 4 drops per titration.

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Signature: Dhanlal De Lloyd, Chem. Dept, The University of The West Indies, St. Augustine campus
The Republic of Trinidad and Tobago.
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