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Acid Base INDICATOR
There are many common household products and garden plants that can be used as pH indicators. Most plants contain pH sensitive anthocyanins, so experiment with other plants, too.
What is an acid-base indicator ?
An acid-base indicator is a weak acid or a weak base. The undissociated form of the indicator is a different color than the iogenic form of the indicator. An Indicator does not change color from pure acid to pure alkaline at specific hydrogen ion concentration, but rather, color change occurs over a range of hydrogen ion concentrations. This range is termed the color change interval. It is expressed as a pH range.
Principle / Mechanism of Indicator :
Weak acids are titrated in the presence of indicators which change under slightly alkaline conditions. Weak bases should be titrated in the presence of indicators which change under slightly acidic conditions.
Common acid-base indicators :
Several acid-base indicators are listed below, some more than once if they can be used over multiple pH ranges. Quantity of indicator in aqueous (aq.) or alcohol (alc.) solution is specified. Tried-and-true indicators include: thymol blue, tropeolin OO, methyl yellow, methyl orange, bromphenol blue, bromcresol green, methyl red, bromthymol blue, phenol red, neutral red, phenolphthalein, thymolphthalein, alizarin yellow, tropeolin O, nitramine, and trinitrobenzoic acid. Data in this table are for sodium salts of thymol blue, bromphenol blue, tetrabromphenol blue, bromcresol green, methyl red, bromthymol blue, phenol red, and cresol red.
Acids
0 - Hydrochloric Acid (HCl)
1.0 - Battery Acid (H2SO4 sulfuric acid)
2.0 - Lemon Juice
2.2 - Vinegar
3.0 - Apples
4.0 - Wine and Beer
4.5 - Tomatoes
6.6 - Milk
Neutral
7.0 - Pure Water
Bases
7.4 - Human Blood
8.3 - Baking Soda (Sodium Bicarbonate)
10.5 - Milk of Magnesia
11.0 - Ammonia
12.4 - Lime (Calcium Hydroxide)
13.0 - Lye
14.0 - Sodium Hydroxide (NaOH
General Acid-Base Indicators
Indicator
pH Range
Quantity per 10 ml
Acid
Base
Thymol Blue
1.2-2.8
1-2 drops 0.1% soln. in aq.
red
yellow
Pentamethoxy red
1.2-2.3
1 drop 0.1% soln. in 70% alc.
red-violet
colorless
Tropeolin OO
1.3-3.2
1 drop 1% aq. soln.
red
yellow
2,4-Dinitrophenol
2.4-4.0
1-2 drops 0.1% soln. in 50% alc.
colorless
yellow
Methyl yellow
2.9-4.0
1 drop 0.1% soln. in 90% alc.
red
yellow
Methyl orange
3.1-4.4
1 drop 0.1% aq. soln.
red
orange
Bromphenol blue
3.0-4.6
1 drop 0.1% aq. soln.
yellow
blue-violet
Tetrabromphenol blue
3.0-4.6
1 drop 0.1% aq. soln.
yellow
blue
Alizarin sodium sulfonate
3.7-5.2
1 drop 0.1% aq. soln.
yellow
violet
α-Naphthyl red
3.7-5.0
1 drop 0.1% soln. in 70% alc.
red
yellow
p-Ethoxychrysoidine
3.5-5.5
1 drop 0.1% aq. soln.
red
yellow
Bromcresol green
4.0-5.6
1 drop 0.1% aq. soln.
yellow
blue
Methyl red
4.4-6.2
1 drop 0.1% aq. soln.
red
yellow
Bromcresol purple
5.2-6.8
1 drop 0.1% aq. soln.
yellow
purple
Chlorphenol red
5.4-6.8
1 drop 0.1% aq. soln.
yellow
red
Bromphenol blue
6.2-7.6
1 drop 0.1% aq. soln.
yellow
blue
p-Nitrophenol
5.0-7.0
1-5 drops 0.1% aq. soln.
colorless
yellow
Azolitmin
5.0-8.0
5 drops 0.5% aq. soln.
red
blue
Phenol red
6.4-8.0
1 drop 0.1% aq. soln.
yellow
red
Neutral red
6.8-8.0
1 drop 0.1% soln. in 70% alc.
red
yellow
Rosolic acid
6.8-8.0
1 drop 0.1% soln. in 90% alc.
yellow
red
Cresol red
7.2-8.8
1 drop 0.1% aq. soln.
yellow
red
α-Naphtholphthalein
7.3-8.7
1-5 drops 0.1% soln. in 70% alc.
rose
green
Tropeolin OOO
7.6-8.9
1 drop 0.1% aq. soln.
yellow
rose-red
Thymol blue
8.0-9.6
1-5 drops 0.1% aq. soln.
yellow
blue
Phenolphthalein
8.0-10.0
1-5 drops 0.1% soln. in 70% alc.
colorless
red
α-Naphtholbenzein
9.0-11.0
1-5 drops 0.1% soln. in 90% alc.
yellow
blue
Thymolphthalein
9.4-10.6
1 drop 0.1% soln. in 90% alc.
colorless
blue
Nile blue
10.1-11.1
1 drop 0.1% aq. soln.
blue
red
Alizarin yellow
10.0-12.0
1 drop 0.1% aq. soln.
yellow
lilac
Salicyl yellow
10.0-12.0
1-5 drops 0.1% soln. in 90% alc.
yellow
orange-brown
Diazo violet
10.1-12.0
1 drop 0.1% aq. soln.
yellow
violet
Tropeolin O
11.0-13.0
1 drop 0.1% aq. soln.
yellow
orange-brown
Nitramine
11.0-13.0
1-2 drops 0.1% soln in 70% alc.
colorless
orange-brown
Poirrier's blue
11.0-13.0
1 drop 0.1% aq. soln.
blue
violet-pink
Trinitrobenzoic acid
12.0-13.4
1 drop 0.1% aq. soln.
colorless
orange-red