School Science Lessons
Acid-base indicators
Updated: 2017-11-12 Sp MF LI
Please send comments to: J.Elfick@uq.edu.au

Acid-base indicators
Table of contents
Chemical indicators, "Serrata", (Commercial
pH meters, "Scientrific", (Commercial)
5.6.0 Acid-base indicators
Indicator Table
37.0 Prepare acid-base indicators
39.0 Prepare standard buffer solutions

Indicator Table
Indicator pH Range Acid Alkali
1.0 Acid fuchsin
5-8
pink
yellow
2.0 Alizarin yellow
10.2-12
yellow
red
3.0 Benzopurpurin
1.2-4.0
violet
red
5.0 Bromocresol green
3.8-5.4
yellow
blue
6.0 Bromocresol purple
5.2-6.8
yellow
purple
7.0 Bromophenol blue
6.0-7.6
yellow
blue
9.0 Chlorophenol red
4.8-6.7
yellow
red
11 Congo red
3.0-5.0
yellow
blue
12 Cresol red
7.2-8.8
yellow
red
14 Indigo carmine
11.6-13
blue
yellow
15 Litmus
4.5-8.3
red
blue
22 Methyl orange 3.1-4.4 red orange
23 Methyl red 4.4-6.3 red yellow
16 Methyl violet
0.15-3.2
yellow
violet
17 Methyl yellow
2.9-4.0
red
yellow
24 Neutral red
6.8-8.0
red
yellow
25 Nitramine
11-13
colourless
brown
26 Orange IV, Tropeolin O O
1.3-3.2
red
yellow
28 Phenol red
6.4-8.4 yellow red
27 Phenolphthalein
8.2-10
colourless
red
34 Thymol blue (1st range)
1.2-2.8
red
yellow
34.1 Thymol blue (2nd range)
8.0-9.6 yellow blue
33 Thymolphthalein 9.3-10.5 colourless blue
35 Trinitrobenzene 12-13.4 colourless orange
36 Universal indicator
1-14
red
violet

1.0 Acid fuchsin
2.0 Alizarin yellow
3.0 Benzopurpurin
4.0
Brilliant yellow
5.0
Bromocresol green
6.0 Bromocresol purple
7.0
Bromophenol blue
Bromophenol red
Bromothymol blue
9.0 Chlorophenol red
10 Clayton yellow
11 Congo red
12 Cresol red
13 Erythrosine
14
Indigo carmine
15 Litmus
16 Methyl violet
17 Methyl yellow
18 Malachite green
19 Metacresol purple
20 Metanil yellow
21 Methyl green
22 Methyl orange
23 Methyl red
24 Neutral red
25 Nitramine
26 Orange IV, Tropeolin O O
27 Phenolphthalein
28 Phenol red
29 Paramethyl red
30 Paranitrophenol
31 Quinaldine red
32 Resazurin
33 Thymolphthalein
34 Thymol blue
35 Trinitrobenzene
36 Universal indicator

5.6.0 Acid-base indicators
Water quality, Water quality test kit, "Scientrific", (Commercial)
12.2.5.0 Acid-base reactions
12.3.16 Dissociation constant, Ka, acidity constant, acid ionization constant
5.6.1 pH and acid-base indicators, acidity and alkalinity, ionization of water
5.6.2 Test common solutions with acid-base indicators
Experiments
19.1.5 Acid-base indicators in the home
8.0 Acid-base neutralization, acid with base forms a salt and water
3.4.4 Litmus paper, electric writing
12.1.11 Rainbow reactions, butyl chloride with sodium hydroxide
19.1.3 Solid acids, add sodium carbonate
19.1.2 Solid acids, pH
19.1.1 Solid acids, solubility
12.3.1 Taste of acids, solid acids in the home
3.53.1 Tests for acid-base indicators
Titration

37.0 Prepare acid-base indicators
37.0 Prepare acid-base indicators
3.53.2 Prepare acid-base plant extract indicators
5.6.11 Goldenrod indicator, electric writing
5.6.13 Prepare beetroot (beet) juice acid-base indicator
5.6.8 Prepare berry juice acid-base indicators
5.6.3 Prepare bromothymol blue acid-base indicator
5.6.4 Prepare methyl orange acid-base indicator
5.6.5 Prepare methyl red acid-base indicator
5.6.6 Prepare phenolphthalein acid-base indicator
5.6.10 Prepare plant extracts acid-base indicators
5.6.9 Prepare red cabbage acid-base indicator
5.6.7 Prepare rose petal acid-base indicator

Acid fuchsin, Andrade's acid fuchsin
1.0 Indicator Table
Acid fuchsin, Andrade's acid fuchsin, acid violet 19, fuchsin S, fuchsin acid, rubine S, C20H17N3Na2O9S3
Add 5 g of acid fuchsin to deionized water.
Add 150 mL of M sodium hydroxide solution.
Mix the solution and leave to stand for one day.
The colour should change from red to brown.
If the solution is not decolorized enough, add 10 mL of M sodium hydroxide solution.
Mix the solution and leave to stand for one day.
Repeat the process until the solution has a straw yellow colour.
Alizarin yellow
2.0 Indicator Table
Alizarin yellow GG
pK: 11.0
pH colour change: 10.0-12.0
Acid: clear, Base: yellow

Alizarin yellow R indicator.
Alizarin yellow, mordant orange l, (sodium salt), azo dye, rust colour, Harmful if ingested.
Alizarin yellow as acid: C13H9N3O5, O2NC6H4N=NC6H3-2-(OH)CO2H, [5-(4-Nitrophenylazo)salicylic acid].
Alizarin yellow as sodium salt, C13H8N3NaO5, [sodium 5-(p-nitrophenylazo)benzenesulfonate].
pH colour change: 10.1-12.0
Acid: yellow, Base: red
Anthraquinone, C14H8O2, (9, 10-dioxanthracene)

Benzopurpurin
3.0 Indicator Table
Benzopurpurin 4B, acid-base indicator, 1-naphthalene sulfonic acid, benzopurpurin 4b, C34H26N6O6S2, sodium salt, direct red
cotton red 4b, red acid dye, changes from blue-violet to red in the pH range 1.2-4.0, formerly used as a stain and as an indicator, for
liquid crystal displays, inks, dyes, micro-organism stains.
16.2.5.2 Azo compounds

3.53.1 Tests for acid-base indicators
Acid-base indicators change colour in acidic or basic solutions.
They may be weak acids that dissociate and change colour in alkaline solutions.
Indicators and colours
Litmus: pH 6 red, pH 7 purple, pH 8 blue
Methyl orange: pH 2.5 red, pH 3.5 straw colour, pH 4.5 orange
Methyl red: pH 4.4 red, pH 6.3 yellow
Phenolphthalein: pH 8.2 colourless, pH 9 pink, pH 10 red, (with excess alkali colourless again)
Universal Indicator: pH 1, 2, 3 red, pH 4 pink, pH 5 orange, pH 6 yellow, pH 7 green, pH 8 green-blue
pH 9 blue, pH 10 blue-violet, pH 11 to 14 violet.
Test the following indicators with acids and bases, e.g. dilute HCl, lemon juice or vinegar, ammonia solution, dilute sodium hydroxide
solution, lime water, tap water, demineralized water:
1. Bromothymol blue solution: pH 6.0 yellow to pH 7.6 blue, in 20% alcohol solution.
Dissolve 0.5 g of bromothymol blue in 500 mL of water.
Add a drop of ammonia solution to turn the solution deep blue in colour.
2. Litmus contains several dyes, including the very sensitive purple-red dye azolitmin, red pH 4.5, blue pH 8.3.
Use red books pH 5 and blue books pH 8 or boil powder litmus for five minutes.
Add drops of nitric acid until a purple colour appears.
Then filter and store in a bottle but keep the solution exposed to the air.
Use a fresh solution before testing pH.
3. Methyl orange is best for solutions with concentration > M/5. Mix 1 g of commercial methyl orange powder with water.
Use 2 drops for each 25 mL of solution in a titration.
4. Methyl Red is a sensitive indicator for titration of weak organic bases and ammonia.
Dissolve 1 g of commercial powder in 500 mL of 60% alcohol.
Use 2 drops for 25 mL of liquid in a titration.
5. Phenolphthalein
5.1 Dissolve 1 g of commercial powder in 500 mL of 50% alcohol.
Add drops of this phenolphthalein solution to 100 mL of 0.5 mol / litre sodium hydroxide solution until a deep pink colour appears.
Divide this solution into 3 test-tubes.
Leave the first test-tube as a control.
Add drops of HCl to the second test-tube until the pink colour disappears.
Add 3 pellets of solid sodium hydroxide to the third test-tube 3 and shake to dissolve.
The pink colour reappears.
5.2 Add colourless phenolphthalein indicator to lime water.
The liquid turns pink.
Blow into the liquid through a drinking straw.
The pink colour disappears and the liquid becomes cloudy.
6. Universal Indicator is a mixture of indicators that causes a colour change for each change in pH value over a wide range.
Note the colour chart on the bottle or package: red pH 1-3 very acidic solution, orange pH 4 to 5 weak acid, yellow pH 6 very weak
acid, green pH 7 neutral, blue pH 8 very weak base, indigo pH 9 to 10 weak base, violet pH 11 to 14 very basic solution.
Use 2 drops of Universal Indicator to 10 mL of test solution.
Test the pH value of lemon juice, vinegar, sodium bicarbonate solution, washing soda, lime water, sodium hydroxide solution, tap water
demineralized water.

3.53.2 Prepare acid-base plant extract indicators
"Red Cabbage Colour Crystals", acid-base indicator, (Commercial)
1. Use plant extracts to "indicate" whether a substance is acidic or basic.
Select brightly coloured flowers or leaves, e.g. rose, Bougainvillaea, hibiscus, geranium, red carnation, (light red with acid and bright
green with alkali), sweet pea, snapdragon, pansy, tulip, willow herb.
The colours are usually caused by anthocyanin water-soluble pigments that change  colour with change in pH.
Boil a fresh unboiled beetroot, red cabbage, tomato skins, (colourless in acid and deep yellow in alkali), blackberry or blackberry jam
damson, elderberry.
Squeeze or grind the plant material with a mortar and pestle with a mixture of 2 mL of acetone and 2 mL of methylated spirit.
Filter the solution, collect the filtrate, and label the indicator, e.g.  "rose extract".
Rose extract colours may be scarlet-pink at pH 1, pale pink at pH 3, green at pH 4, yellow-brown at pH 7 and orange at pH 12.
Use universal indicator solution to test the plant indicators.
Indicators made from plants are mostly red with acids but yellow, green or purple with alkalis.
2. Test common substances and note the colour change of the plant extract indicator, e.g. ammonia solution, antacid tablet solution
baking soda solution, bleaching powder solution, coconut milk, coffee grounds, fertilizer solution, fruit juice, lemon juice, lemonade
lime water, red cabbage juice, saliva, soap solution, sugar solution, vinegar, tap water, tea bag in hot water, whitewash.
Estimate the range of pH tested by the plant extract indicators.
3. Soak cut pieces of red cabbage leaf in boiling water for 30 minutes then remove them.
Pour red cabbage water into the following solutions:
3.1 water, stays violet, 3.2 white vinegar, turns red, 3.3 baking soda solution, turns green.
Also, use the liquid from a container of pickled cabbage.
4. Fresh grape juice turns red in acid lemonade and blue in alkaline dishwater.
5. Put spots of plant extract indicators on absorbent paper and leave to dry.
Put one drop of lemon juice on each spot and note the colour change.
These are alkaline, basic, substances.
Note whether they all give the same colour.
Plant extracts can act as indicators to test whether a substance is acidic or basic.
6. Put some original filtrate on to another piece of filter paper.
When the filter paper is dry, note the colours given by sodium bicarbonate solution, washing soda, lime water and a dilute solution of
sodium hydroxide.
These are alkaline, basic, substances.
Note whether they all give the same colour.
Plant extracts can act as indicators to test whether a substance is acidic or basic.
7. Add a few drops of sodium bicarbonate solution to 1 mL of flower extract indicator in a test-tube.
Then add lemon juice and note any colour change.
8. Repeat the experiment with lime water and indicator followed by dilute hydrochloric acid.
Note any colour change.
Note whether the original colour returns after by adding more lime water.
Note how many times the indicator colour can change before the test-tube is full.
9. Do NOT taste these acids in the laboratory.
Taste lemon juice, vinegar and cream of tartar at home.
Each acid has a sour taste that is a characteristic of acids.
Lemon juice contains the white crystalline citric acid.
Vinegar contains ethanoic acid, (acetic acid, CH3COOH).
Cream of tartar contains the acid salt potassium hydrogen tartrate, the purified form of argol that occurs as brown crystals in fermenting
wine.
10. Wave a bluebell flower closely over an ant nest.
The angry ants rush out to squirt formic acid on the bluebell flower and the blue pigment in the petals turns red.

4.0 Brilliant yellow
Brilliant yellow, direct yellow 4, C26H18N4Na2O8S2
pH colour change: 6.6-7.8
Acid: yellow, Base: orange

Bromocresol green
5.0 Indicator Table
Bromocresol green, (3',3'',5',5''-tetrabromo-m-cresol-sulfonephthalein), C21H14Br4O5S
pK: 4.90
pH colour change: 3.8-5.4
Acid: yellow, Base: dark blue
Used as a tracking dye.
Prepare bromocresol green solution, 0.1 g in 14.3 mL of M NaOH + 235.7 mL of water

5.6.1 pH and acid-base indicators, acidity and alkalinity, ionization of water
The pH tests use an indicator that changes colour with changes in the concentration of hydrogen ions, or the acidity of the solution.
The pH scale (Peter Sorensen 1868 - 1939) is a scale of acidity and alkalinity that runs from pH 0, most acid, to pH 14, most alkaline.
A neutral solution has pH = 7, an acid solution has pH < 7, and a basic or alkaline solution has pH >7.
The term "pH" stands for "power of hydrogen" and measures the concentration of hydrogen ions in water.
The pH scale is logarithmic so a pH 4 solution is ten times more acidic than a pH 5 solution.
pH = -log10(H+), where (H+) = concentration of hydrogen ions.
(OH-) = concentration of hydroxyl ions.
For water (H+)(OH-) = 1 X 10-14 at 25oC.
Pure water is neutral where (H+) = (OH-) = 1 X 10-7 M, i.e. at pH 7.
For acid solutions (H+) is greater than (OH-), so pH is less than 7 (0 to 7).
For alkaline solutions (H+) is less than (OH-), so pH is greater than 7 (7 to 14).
To convert pH to hydrogen ion molar concentration, [H3O+] = Antilog(-pH), so if pH = 2.55, [H3O+]
= Antilog(-2.55) = 2.8 X 10-3 M.
Ionization of water
2H2O <--> H3O+ + OH- (25oC) Ka =1.00 X 10-14, pKa = 14.00
2H2O <--> H3O+ + OH- (0oC) Ka = 0.11 X 10-14, pKa = 14.94

5.6.2 Test common solutions with acid-base indicators
Acid-base indicators change colour in acidic or basic solutions.
They may be weak acids that dissociate and change colour in alkaline solutions.
Test acid-base indicators with dilute HCl, lemon juice, vinegar, ammonia solution, dilute sodium
hydroxide solution, lime water, tap water, demineralized water.

5.6.3 Bromothymol blue
Bromothymol blue, Prepare bromothymol blue acid-base indicator
pH < 6.0 yellow to pH > 7.6 blue, in 20% alcohol solution.
Dissolve 0.5 g of bromothymol blue in 500 mL of water.
Add a drop of ammonia solution to turn the solution deep blue in colour.

5.6.4 Methyl orange
Methyl orange, (acid-base indicator), C14H14N3NaO3S
Prepare methyl orange acid-base indicator, pH < 3.1 red to pH > 4.4 yellow-orange.
It is best for solutions with concentration > M/5.
Mix 1 g of commercial methyl orange powder with water.
Use 2 drops for each 25 mL of solution in a titration.
1. Use as a 0.1% solution in 20% ethanol
2. Put a finger width of the methyl orange powder in the test-tube and add water to half fill the test-tube.
Shake to make the powder dissolve.
Add tartaric acid powder until the colour changes to red.
Sodium carbonate change this red liquid to orange.
Add a finger width of sodium carbonate to the red liquid until the colour changes back to orange again.
Shake the test-tube to help the mixing.

5.6.5 Methyl red
Methyl red, Prepare methyl red acid-base indicator
pH <4.2 red to pH > 6.3 yellow
1. It is a sensitive indicator for titration of weak organic bases and ammonia.
Dissolve 1 g of commercial powder in 500 mL of 60% alcohol.
Use 2 drops for 25 mL of liquid in a titration.
2. Dissolve 0.04 g of methyl red in 40 mL of ethanol and make up to 100 mL with water.
3. Dissolve 0.02 g in 60 mL of ETOH + 40 mL of water.

5.6.6 Phenolphthalein
Phenolphthalein, Prepare phenolphthalein acid-base indicator
Phenolphthalein, C20H14O4, indicator in acid-base titrations, (acid- colourless, base-pink), a weak acid, former laxative, prepared from
phthalic anhydride, C6H4(CO)2O (FLAM + 13oC 1170) pH 10 red, with excess alkali colourless again
1. Add 5 g to 500 mL of ethanol, add 500 mL water. Stir.
2. Dissolve 1 g of commercial powder in 500 mL of 50% alcohol.
Add drops of this phenolphthalein solution to 100 mL of 0.5 mol / litre sodium hydroxide solution until a deep pink colour appears.
Divide this solution into 3 test-tubes.
Leave the first test-tube as a control.
Add drops of HCl to the second test-tube until the pink colour disappears.
Add 3 pellets of solid sodium hydroxide to the third test-tube.
Shake to dissolve.
The pink colour reappears.
3. Add colourless phenolphthalein indicator to lime water.
The liquid turns pink.
Blow into the liquid through a drinking straw.
The pink colour disappears and the liquid becomes cloudy.

5.6.7 Prepare rose petal acid-base indicator
1. Boil red rose petals in some water until the petals have almost lost their colour and a pink solution forms.
Test this pink solution with acids and bases.
2. Wave a bluebell flower closely over an ant nest.
The angry ants rush out to squirt formic acid on the bluebell flower and the blue pigment in the petals turns red.

5.6.8 Prepare berry juice acid-base indicators
Test the juices from stewed blackberries, black currants, and raspberries.
Also, mix a spoonful of fruit jam with warm water then filter it to get a colourless liquid.
Test the solution with acids and bases.

5.6.9 Prepare red cabbage acid-base indicator
1. Soak cut pieces of red cabbage leaf in boiling water for 30 minutes then remove them.
Pour cabbage water into:
1.1 water, it stays violet
1.2 white vinegar, it turns red
1.3 baking soda solution or ammonia solution, it turns green.
2. Boil shredded red cabbage for 15 minutes then squeeze out the juice. Fry an egg.
When the "white" of the egg is about to change from colourless to white as the protein albumin denatures, add some red cabbage juice.
The "white" of the egg turns green.
3. Use the liquid from a container of pickled cabbage as an acid-base indicator
4. Use the green water juices from boiled cabbage as an acid-base indicator.

5.6.10 Prepare plant extracts acid-base indicators
"Red Cabbage Colour Crystals", acid-base indicator, (Commercial)
1. Use plant extracts to "indicate" whether a substance is acidic or basic.
Select brightly coloured flowers or leaves, e.g.  rose, Bougainvillaea, hibiscus, geranium, red carnation, (light red with acid and bright
green with alkali), sweet pea, snapdragon, pansy, tulip, willow herb.
The colours are usually caused by anthocyanin water-soluble pigments that change colour with change in pH.
Boil a fresh unboiled beetroot, red cabbage, tomato skins (colourless in acid and deep yellow in alkali), blackberry or blackberry jam
damson, elderberry.
Squeeze or grind the plant material with a mortar and pestle with a mixture of 2 mL of acetone and 2 mL of  methylated spirit.
Filter the solution, collect the filtrate, and label the indicator, e.g. "rose extract".
Rose extract colours may be scarlet-pink at pH 1, pale pink at pH 3, green at pH 4, yellow-brown at pH 7  and orange at pH 12.
Use universal indicator solution to test the plant indicators.
Indicators made from plants are mostly red with acids but yellow, green or purple with alkalis.
2. Test common substances and note the colour change of the plant extract indicator, e.g. ammonia solution,  antacid tablet solution
baking soda solution, bleaching powder solution, coconut milk, coffee grounds, fertilizer solution, fruit juice, lemon juice, lemonade
lime water, red cabbage juice, saliva, soap solution, sugar solution,  vinegar, tap water, tea bag in hot water, whitewash.
Estimate the range of pH tested by the plant extract indicators.
3. Fresh grape juice turns red in acid lemonade and blue in alkaline dishwater.
4. Put spots of plant extract indicators on absorbent paper and leave to dry.
Put one drop of lemon juice on each spot and note the colour change.
Note the colours given by sodium bicarbonate solution, washing soda, lime water and a dilute solution of sodium  hydroxide.
These are alkaline, basic, substances.
Note whether they all give the same colour.
Plant extracts can act as indicators to test whether a substance is acidic or basic.
5. Add a few drops of sodium bicarbonate solution to 1 mL of flower extract indicator in a test-tube.
Then add lemon juice and note any colour change.
6. Repeat the experiment with lime water and indicator followed by dilute hydrochloric acid.
Note any colour change.
Note whether the original colour returns after by adding more lime water.
Note how many times the indicator colour can change before the test-tube is full.

5.6.11 Goldenrod indicator paper, C.I.
Direct Yellow 4 "Goldenrod", (Commercial)
Goldenrod paper is coated with a dye from turmeric that acts as an acid-base indicator.
It turns bright red in contact with bases and back to its normal golden colour in contact with acids, (vinegar, lemon juice).
Use it to test household items, e.g.  (soaps, milk, juice, drinks, food, to determine if they are acidic or alkaline (basic).
Electric writing
Dip goldenrod indicator paper in salt water and place it on aluminium foil.
Connect the positive terminal of a battery to the foil using crocodile clips.
Connect a loose wire to the negative battery terminal.
Drag the end of the loose wire across the wet goldenrod indicator paper to create red writing.
If you reverse the polarity of the battery to erase the red writing.
Repeat the experiment with goldenrod indicator paper dipped in dilute ammonia solution.

5.6.13 Prepare beetroot (beet) juice acid-base indicator
1. Crush beetroot and use the juice as an acid-base indicator.
Add ammonia solution for red to dark purple colour change.
Adding vinegar for red colour to return.
Some teachers report yellow with sodium hydroxide, purple with ammonia solution and pink with acids.
2. The red colour of beetroot comes from betacyanin pigments.
Beetroot acid-base indicators have optical stability at pH 4 to 5 but are structurally unstable at extremes of pH.
So the red colour in urine after eating beetroot depends on urine pH and the pigments not being broken down by digestion processes.
Eating excess beetroot as in borscht soup usually causes red or pink urine.

Bromocresol purple
6.0 Indicator Table
Bromocresol purple, acid-base indicator, C21H16Br2O5S, dibromo-0-cresolsulfone phthalein
Prepare bromocresol purple indicator, 0.1 g bromocresol purple in 18.5 mL 0.01 M NaOH + 231.5 mL of water.

Bromophenol red, acid-base indicator
Bromophenol red, C19H12Br2O5S, 3'3"-Dibromophenolsulphonphthalein
pH colour change: 5.2-6.8
Acid: yellow, Base: red

Bromophenol blue
7.0 Indicator Table
Bromophenol blue, C19H10Br4O5S, (tetrabromophenolsulfonephthalein, 2-bromo-2-methylbutane, t-butyl bromide
pK: 4.10, dye, [dichromatism, See 27.124 Dichromatism, bromophenol blue, resazurin, pumpkin seed oil]
pH colour change: 3.0-4.6
Acid: yellow, Base: purple
Prepare bromophenol blue solution, 0.1 g in 149 mL 0.01 M NaOH + 235.1 mL of water.

Bromothymol blue
Bromothymol blue, bromthymol blue, (dibromothymolsulfophthalein), C27H28Br2O5S, weak acid,
pK: 7.30
pH colour change: 6.0-7.6
Acid: yellow, Base: blue, Neutral: Green
Prepare bromothymol blue acid-base indicator: 5.6.3

Chlorophenol red
9.0 Indicator Table
Chlorophenol red, (dichlorophenolsulfonephthalein), C19H12Cl2O5S
pK: 6.25
pH colour change: 4.8-6.7
Acid: yellow, Base: red / violet
It can detect chlorine dioxide in drinking water, green to brown-green or brown powder, crystalline powder, crystals, granules or lumps
soluble in ethanol, has a "pharmacy smell".
16.1.3.2.1: Carbolic acid, phenol

10. Clayton yellow
Clayton yellow, direct yellow 9, titan yellow, thiazol yellow G, mimosa, C28H19N5O6S4Na2
pH colour change: 12.2-13.2
Acid: yellow, Base: amber

Congo red
11. Indicator Table
Congo red, C32H22N6Na2O6S2
Congo Red 4B, Cosmos Red, Cotton Red B, Cotton Red C, Direct Red 28, Direct Red R
pH colour change: 3.0-5.0
Acid: blue, Base: red
Prepare congo red solution, 01% solution in water.
Microscopy stain, blue in acid and red in alkali, made from coal tar. for dialysis diffusion experiments and as a yeast stain.

Cresol red
12. Indicator Table
Cresol red, indicator grade, (o-cresolsulfonephthalein), C21H18O5S
pH colour change: 0.4-1.8
Acid: red, Base: yellow
Prepare cresol red acid solution, 0.1 g in 26.2 mL 0.01 M NaOH + 223.8 mL water

12.1 Cresol Red, Na salt, indicator grade, C21H17NaO5S
pH colour change: 7.0-8.8
Acid: yellow, Base: red
Triarylmethane dye, used to monitor the pH in aquarium water, electrophoresis, irritates eyes, do not ingest it.
m-cresol, 3-hydroxytoluene, Highly toxic by all routes, lung irritant vapour, highly corrosive to skin
m-cresol, Solution < 12%, Not hazardous
Prepare cresol red basic solution, 0.1 g in 26.2 mL 0.01 M NaOH + 223.8 mL water.
Cresols: 16.1.3.2.3

13. Erythrosin
Erythrosin B, Solvent Red 140, C20H8I4O5
Erythrosine, sodium salt, C20H6I4Na2O5, Red No.3
Cherry pink food colouring, E127, used to detect dental plaque
pH colour change: 2.2-3.6
Acid: orange, Base: red

Indigo carmine
14. Indicator Table
Indigo carmine, (acid-base indicator), microscopy stain, Toxic if ingested, decolorized by oxidizing agents, e.g. ozone.
Indigo carmine, sodium indigotin, disulfonate soluble indigo blue
Indigo carmine, Oxidation of glucose with sodium hydroxide and methylene blue.
Blue bottle experiment: 16.3.7.2, (See 3.3)
Synthetic food colours approved for use in Australia, Blue shadow, CI 73015 Indigo carmine

Litmus
15
. Indicator Table
Laboratory equipment, Test Paper Litmus, Blue, Red, pack 100 strips, "Scientrific", (Commercial )
1. Litmus paper contains several dyes, including the very sensitive purple-red dye azolitmin, red pH 4.5, blue pH 8.3.
Use red books pH 5 and blue books pH 8.
Litmus is also available as granulated litmus, (tournesol), powdered litmus.
Litmus, litmus solution, granulated litmus, tournesol
Litmus paper, 20 sheets per booklet, pack / 10 booklets.
Litmus paper has the acid / base indicator absorbed into it.
Litmus powder blue colouring agent may irritate the eyes. Used to colour beverages.
Litmus acid / indicator is extracted mainly from the lichen Rocella tinctoria
2. Experiments
Litmus paper, electric writing: 3.4.4
Litmus tests for ammonia: 3.33.1.3
Litmus tests for hydrogen gas: 3.41.1.1
Litmus tests for carbon dioxide: 3.34.1.5
Litmus paper test for hydrogen chloride: 3.42.1.2
3. Prepare litmus solution 1
Boil 10 g crushed litmus powder in 500 mL water for five minutes.
Leave to stand, then filter the solution and store in a bottle.
Add drops of nitric acid until a purple colour appears.
Then filter and store in a bottle but keep the solution exposed to the air.
Use a fresh solution before testing pH.
Litmus solution can from blue to red.
Put a finger width of litmus powder in the test-tube, and add water.
Shake to make the powder dissolve.
Add a finger width of tartaric acid powder until the colour changes to red.
Sodium carbonate can change this red liquid to blue.
Add a finger width of sodium carbonate to the red liquid until the colour changes back to blue.
Shake the test-tube to help the mixing.
4. Prepare litmus solution 2
Grind 250 g of granular litmus and put it in a flask with 500 mL of 40% ethanol.
Heat and boil the solution for one minute.
Decant the liquid to storage leaving a residue in the flask. Add 500 mL of 40% ethanol to the residue.
Heat and boil the solution for one minute, then add it to the stored decanted liquid.
Centrifuge the solution and adjust the volume of the supernatant to 1000 mL with 40% ethanol.
Add M hydrochloric acid drop by drop until the solution becomes purple.
Test the solution by boiling 10 mL of deionized water, leave to cool, add one drop of the litmus solution.
Mix the drop with the water and the water should become mauve in colour.
For laboratory use, make a 2.5% solution on the litmus indicator in deionized water.

Methyl violet
16
. Indicator Table
Methyl violet, 2B, basic violet 1, C24H28N3Cl, Paris violet, green crystalline powder, metal lustre
pH 0.15 yellow to pH 3.2 blue-violet
Use as 01 - 0.05 % in water
Use as 0.1 % solution microscopy stain

Methyl violet 10B, basic violet 3, C25H30N3Cl, gentian violet, crystal violet
pH colour change: 0.0-1.8
Acid: yellow, Base: blue violet
Crystal violet, (C.I. 42555, C.I. basic violet 3), C25N3H30Cl, Toxic if ingested
Crystal violet 10% W / V alcoholic: 3.11.1
Prepare crystal violet solution, 0.02% solution in water.
Gentian violet 10B, C25H30ClN3, (CI: 42535), (1% solution), bactericide, anti-fungal

Methyl yellow
17
. Indicator Table
Methyl yellow, (dimethyl yellow), C14H15N3
pK: 3.25
pH colour change: 2.9-4.0
Acid: red, Base: yellow
C.I. 11020
In aqueous solution at low pH, methyl yellow appears red. pH 2.9 and 4.0, becomes yellow above pH 4.0.

18. Malachite green
Malachite green, [C6H5C(C6H4N(CH3)2)2]Cl
pK: 1.0
pH colour change: 0.2-1.8
Acid: yellow, Base: blue-green
Used with carbol fuchsin in Sigma Acid Fast Stain as a counterstain and a differentiation.
Malachite Green oxalate salt, (N,N,N,N-Tetramethyl-4,4-diaminotriphenylcarbenium oxalate), Basic Green 4
(C23H25N2.C2HO4.0.5C2H2O4), counterstain for paraffin-embedded botanical material, spore stain for bacteria.
Prepare malachite green oxalate solution: malachite green oxalate 1.5%; acetic acid, 10%; and glycerol, 17%, in deionized water.
Food dye banned in food industry, same colour as malachite mineral, copper carbonate hydroxide, Cu2CO3(OH)2.

19. Metacresol purple
Metacresol purple, (in acid solution), C21H18O5S, m-cresol purple, m-cresolsulfonphthalein,cresol purple
pK: ~2.0
pH colour change: 1.2-2.8
Acid: red, Base: yellow
m-cresol purple sodium salt, C21H17NaO5S, m-cresolsulfonphthalein sodium salt, stain and dye

Metacresol purple, (in basic solution), (m-cresol purple, cresol purple, m-cresolsulfonephthalein)
pK: 8.32
pH colour change: 7.6-9.2
Acid: yellow, Base: purple-red
Prepare metacresol purple basic solution, 0.1 g in 26.2 mL 0.01 M NaOH + 223.8 mL water.

20. Metanil yellow
Metanil yellow, [3-(4-Anilinophenylazo)benzenesulfonic acid sodium salt], acid yellow 36, C18H14N3NaO3S
(m-(p-anilinophenylazo)benzene sulfonate), Na - salt
pH colour change: 1.5-2.7
Acid: red, Base: yellow
Prepare metanil solution, 0.01% solution in water.

21. Methyl green
Methyl green, pyronin 100, ethyl green
monobromomonochloro ZnCl2 salt: C27H35BrClN3.ZnCl2
acid-base indicator
pH 0.2 yellow - pH 1.8 blue
Methyl green, Use as 0.1% solution in water.
Prepare methyl green solution, 0.1% solution in water.
Used to stain chromatin in microscopy.

Methyl orange
22. Indicator Table
Methyl orange, C14H14N3NaO3S
pK: 3.46
pH colour change: 3.1-4.4
Acid: red, Base: orange-yellow
Prepare as methyl orange solution, 0.01% solution in water.
Prepare buffered solution, methyl orange: 12.10.7.3
Prepare methyl orange acid-base indicator : 5.6.4
Salt effect on buffer solutions: 12.10.7.4

Methyl red
23. Indicator Table
Methyl red, [2-(4-Dimethylaminophenylazo)benzoic acid, 4-Dimethylaminoazobenzene-2-carboxylic acid], acid red 2
(CH3)2NC6H4N=NC6H4CO2H
pK: 5.00
pH colour change: 4.4-6.0
Acid: red, Base: yellow
Prepare methyl red solution: 5.6.5

Neutral red
24. Indicator Table
Neutral red, C15H17ClN4
(3-Amino-7-dimethylamino-2-methylphenazine hydrochloride), toluylene red, amino dimethyl amino toluminozine
C.I. Red Base 5, toluidine red, Toxic if ingested, microscopy stain
red pH < 6.8 to yellow pH > 8.0
Prepare neutral red stain:
1. 0.1 g neutral red, 100 mL deionized water, Dilute 1 in 10.
2. Mix 0.1 g stain + 0.2 mL 1% acetic acid + 100 mL water. Use as 1% solution in 59% ethanol.
pH colour change: 6.8-8.0
Acid: red, Base: amber

Nitramine
25
. Indicator Table
Nitramine, (acid-base indicator, 3.5), C7H5N5O8, tetryl, colourless-yellow crystals, explosive formerly for munitions
Nitramine: 16.2.4.3.04

Orange IV
26. Indicator Table
Orange IV, (acid-base indicator, 1.3), C18H14N3O3SNa,  monosodiumsalt, orange G, acid orange, tropaeolin 00, benzenesulfonic acid
orange-yellow powder, soluble in water and alcohol
Prepare as 0.01% solution in water.
Microscopy stain: 3.21

Phenolphthalein
27. Indicator Table
Phenolphthalein, C20H14O4
[3,3-Bis(4-hydroxyphenyl)-1(3H)-isobenzofuranone]
See: Laboratory equipment, Test paper, phenolphthalein, "Scientrific", (Commercial )
pK: 9.5
pH colour change: 8.0-9.8
Acid: clear, Base: red-violet
Prepare phenolphthalein acid-base indicator: 5.6.6

Phenol red
28. Indicator Table
Phenol red, C19H14O5S, phenolsulfonephthalein, Toxic if ingested
pK: 8.00
pH 6.8 - 8.2, yellow to red
Used to test pH in swimming pools. It can measure pH from 6.8 to 8.4.
The tablet form usually incorporates a chlorine neutralizer for more accurate results.
Phenol red, some preparations give a bright pink colour at pH 8.1

29. Paramethyl red
Paramethyl red, p-methyl red, [4-dimethylaminoazobenzene-4'-carboxylic acid], [sodium p-(p-dimethylaminophenylazo)-benzoate]
C15H15N3O2
pH colour change: 1.0-3.0
Acid: red, Base: yellow

30. Paranitrophenol
Paranitrophenol, p-nitrophenol, C6H5NO3
pK: 7.15
pH colour change: 5.6-7.6
Acid: colourless, Base: yellow

31. Quinaldine red
Quinaldine red, [2-(4-Dimethylaminostyryl)-1-ethylquinolinium iodide], C21H23IN2
pH colour change: 1.0-2.2
Acid: clear, Base: red

32. Resazurin, C12H7NO4, sodium salt, C12H6NNaO4
pH colour change: 3.8-6.4
Acid: orange, Base: violet
Resazurin stain, test for milk: 16.1.6

Thymolphthalein
33
. Indicator Table
Thymolphthalein, C28H30O4, ACS reagent, (5,5-Diisopropyl-2,2-dimethylphenolphthalein)
pK: 9.7
pH colour change:
pH 8.8 colourless to 10.5 blue
Tests for carbon dioxide, thymolphthalein indicator: 3.34.1.6

Thymol blue, 1st range
34. Indicator Table
Thymol blue, 1st range, acid solution, (thymolsulfonephthalein), C10H16, Harmful if ingested
pK: 1.65
pH colour change: 1.2-2.8
Acid: red, Base: yellow

Thymol blue, 2nd range
34.1 Indicator Table
Thymol blue, 2nd range, basic solution, (thymolsulfonephthalein), C10H16, Harmful if ingested
pK: 9.20, pH colour change: 8.0-9.6
Acid: yellow, Base: blue

Trinitrobenzene
35. Indicator Table
Trinitrobenzene, C6H3N3O6, (1,3,5-trinitrobenzene)
Chromatography

Universal indicator
36
. Indicator Table
Laboratory equipment, Test paper, universal indicator, pH 1-14,  "Scientrific", (Commercial )
Indicator papers, pH 0 to 14, strips, pack / 100
Indicator papers, pH 0 to 14, 30 second, 5 m reel
Buffer salt, universal indicator: 12.10.9

Experiments
1. Prepare universal indicator.
Dissolve the following in 500 mL ethanol: 0.0250 g thymol blue, 0.0625g methyl red, 0.5 g phenolphthalein, 0.25 g bromothymol blue.
Dilute this solution to 1 litre with deionized water.
Add drops of 0.05 M sodium hydroxide until mixture is green.
2. Universal indicator test paper, (FLAM 1142), is mixture of acid-base indicators that causes a colour change for each change in pH
value over a wide range.
Note the colour chart on the bottle or package: Red pH 1-3 (strong acid solution)
Orange pH 4-5 (weak acid) (Pink pH 4), Yellow pH 6 (weaker acid), Green or pale green pH 7 (neutral)
Blue or green-blue pH 8 (very weak base), Indigo pH 9-10 (weak base) (Blue pH 9) (Blue-violet pH 10),  Violet pH 11 to 14
(very basic solution)
3. Use 2 drops of Universal Indicator to 10 mL of test solution.
Test the pH value of the following substances: baking soda solution, demineralized water, dill pickle juice, distilled water, household
ammonia, liquid soap, pineapple juice, sodium bicarbonate solution, tap water, lemon juice, lime water, sodium hydroxide solution
vinegar, washing soda, "Windex" window cleaning solution.
4. Dissolve in 500 mL ethanol: 0.0250 g thymol blue, 0.0625 g methyl red, 0.5000 g phenolphthalein, 0.2500 g bromothymol blue.
Dilute this solution to 1 litre with deionized water.
Add drops of 0.05 M sodium hydroxide until the mixture is green.
5. Test colours of universal indicator
Slowly neutralize lime water containing universal indicator, by adding acid drop by drop.
Describe what you see.
The starting colour is blue.
As citric acid is added the colour changes because the acid keeps weakening the alkali, neutralizes it exactly (pale green colour), and
thereafter gradually builds up its own strength.
red: strong acid | orange: weak acid | yellow : weaker acid | pale green: neutral | green: weaker acid | blue: weak acid
| violet: strong alkali
6. Make a very dilute solution of citric acid by adding 7 g of citric acid to one litre of water.
Put two test-tubes of lime water in a beaker.
Put a piece of universal indicator paper in each beaker.
Stir until an inky blue solution forms then remove the universal indicator paper.
Add citric acid to the beaker, drop by drop.
Note that although much acid has to be added to form the different colours, it is the last drop that causes one colour to change into
another.
If you miss a colour by adding the acid too quickly, add lime water to the beaker to restore the blue colour and start again.
To make the colours more easily seen, put the beaker on a white tile.
Citric acid is not a strong acid.

37. Prepare acid-base indicators
Indicator pH Range | Quantity per 10 ml | Acid Base
2,4-Dinitrophenol | pH 2.4-4.0 | 1-2 drops 0.1% solution in 50% alcohol | colourless yellow
α-Naphtholbenzein | pH 9.0-11.0 | 1-5 drops 0.1% solution in 90% alcohol | yellow blue
α-Naphtholphthalein | pH 7.3-8.7 | 1-5 drops 0.1% solution in 70% alcohol | rose green
α-Naphthyl red | pH 3.7-5.0 | 1 drop 0.1% solution in 70% alcohol | red yellow
Alizarin sodium sulfonate | pH 3.7-5.2 | 1 drop 0.1% aqueous solution | yellow violet
Alizarin yellow | pH 10.0-12.0 | 1 drop 0.1% aqueous solution | yellow lilac
Azolitmin | pH 5.0-8.0 | 5 drops 0.5% aqueous solution | red blue
Bromocresol green | pH 4.0-5.6 | 1 drop 0.1% aqueous solution | yellow blue
Bromocresol purple | pH 5.2-6.8 | 1 drop 0.1% aqueous solution | yellow purple
Bromophenol blue | pH 3.0-4.6 | 1 drop 0.1% aqueous solution | yellow blue-violet
Bromphenol blue | pH 6.2-7.6 | 1 drop 0.1% aqueous solution | yellow blue
Chlorphenol red | pH 5.4-6.8 | 1 drop 0.1% aqueous solution | yellow red
Cresol red | pH 7.2-8.8 | 1 drop 0.1% aqueous solution | yellow red
Diazo violet | pH 10.1-12.0 | 1 drop 0.1% aqueous solution | yellow violet
Methyl orange | pH 3.1-4.4 | 1 drop 0.1% aqueous solution | red orange
Methyl red | pH 4.4-6.2 | 1 drop 0.1% aqueous solution | red yellow
Methyl yellow | pH 2.9-4.0 | 1 drop 0.1% solution in 90% alcohol | red yellow
Neutral red | pH 6.8-8.0 | 1 drop 0.1% solution in 70% alcohol | red yellow
Nile blue | pH 10.1-11.1 | 1 drop 0.1% aqueous solution | blue red
Nitramine | pH 11.0-13.0 | 1-2 drops 0.1% solution in 70% alcohol | colourless orange-brown
Orange IV, tropaeolin | pH OO 1.3-3.2 | 1 drop 1% aqueous solution | red yellow
p-Ethoxychrysoidine | pH 3.5-5.5 | 1 drop 0.1% aqueous solution | red yellow
p-Nitrophenol | pH 5.0-7.0 | 1-5 drops 0.1% aqueous solution | colourless yellow
Pentamethoxy red | pH 1.2-2.3 | 1 drop 0.1% solution in 70% alcohol | red-violet colourless
Phenol red | pH 6.4-8.0 | 1 drop 0.1% aqueous solution | yellow red
Phenolphthalein | pH 8.0-10.0 | 1-5 drops 0.1% solution in 70% alcohol | colourless red
Poirrier's blue | pH 11.0-13.0 | 1 drop 0.1% aqueous solution | blue violet-pink
Rosolic acid | pH 6.8-8.0 | 1 drop 0.1% solution in 90% alcohol yellow red
Salicyl yellow | pH 10.0-12.0 | 1-5 drops 0.1% solution in 90% alcohol | yellow orange-brown
Tetrabromphenol blue | pH 3.0-4.6 | 1 drop 0.1% aqueous solution | yellow blue
Thymol Blue | pH 1.2-2.8 | 1-2 drops 0.1% solution in aqueous | red yellow
Thymol blue | pH 8.0-9.6 | 1-5 drops 0.1% aqueous solution | yellow blue
Thymolphthalein | pH 9.4-10.6 | 1 drop 0.1% solution in 90% alcohol | colourless blue
Trinitrobenzoic acid | pH 12.0-13.4 | 1 drop 0.1% aqueous solution | colourless orange-red
Tropaeolin O | pH 11.0-13.0 1 drop 0.1% aqueous solution yellow | orange-brown
Tropaeolin OO | pH 1.3-3.2 | 1 drop 1% aqueous solution | red yellow
Tropaeolin OOO | pH 7.6-8.9 | 1 drop 0.1% aqueous solution | yellow rose-red

38. Chemicals standards
ACS: Reagent
GR: (Guaranteed Reagent)
AR: (Analytical Reagent)
Primary standards
Reagent
OR: (Organic reagent)
Purified
Practical
Lab Grade
USP
NF: (National Formulary)
FCC
CP: (Chemically Pure)
Technical

Chemicals standards
ACS Reagent, (American Chemical Society), high quality chemical for laboratory use.
GR, (Guaranteed Reagent), for analytical chemistry, meet or exceeds ACS requirements.
AR, Analytical Reagent, for laboratory and general use, also AR (ACS).
Primary Standard, AR of exceptional purity, for standardizing volumetric solutions and reference standards.
Reagent, highest quality commercially available, no set specifications.
OR, (Organic reagent), for research.
Purified, good quality, no official standard inorganic chemical.
Practical, good quality, no official standards, general applications.
Practical grade organic chemicals may contain isomers of intermediates.
Lab Grade, for histology methods and general applications.
USP, (US Pharmacopoeia).
USP / GenAR, (European Pharmacopoeia, PhEur, EP), and British Pharmacopoeia, (BP).
NF, (National Formulary).
The United States Pharmacopoeia and The National Formulary, (USPNF), is a book of public pharmacopoeia standards.
It contains standards for (chemical and biological drug substances, dosage forms, and compounded preparations), excipients, medical
devices, and dietary supplements.
FCC, (Food Chemical Codex).
CP, (Chemically Pure), general applications.
Technical, general industrial use.

39.0 Prepare standard buffer solutions
The table below shows how to prepare buffer solutions for a particular pH by mixing pairs of the following four solutions:
Solution A = 0.l M boric acid:
Dissolve 3.09 g AR boric acid and 3.73 g potassium chloride in water and make up the solution to 500 mL in a measuring cylinder.
Solution B = 0.l M sodium hydroxide:
Dilute standard sodium hydroxide.
Solution C = 0.l M citric acid:
Dissolve 9.60 g AR citric acid in water and make up the solution to 500 mL in a measuring cylinder.
Solution D = 0.2 M disodium hydrogen phosphate:
Dissolve 17.82 g Na2HPO4.2H2O in water, and make up the solution to 500 mL in a measuring cylinder.
Table 39.0 Standard buffer solutions.
pH Solution A Solution B pH Solution C Solution D
-
mL mL -
mL mL
10.0 25 21.8 6.0 14.6 25
9.6 25 18.0 5.6 18.1 25
9.2 25 13.0 5.2 21.6 25
8.8 25 8.0 4.8 25 24.3
8.4 25 4.0 4.4 25 19.8
8.0 1.4 50 4.0 25 15.7
7.6 3.4 50 3.6 25 11.9
7.2 3.8 25 3.2 25 8.2
6.8 7.4 25 2.8 25 8.2
6.4 11.1 25 2.4 50 3.4