School Science Lessons
2009-10-06
Acid-base indicators
Indicator pH Range Quantity of indicator per 10 mL Acid Alkali
Universal indicator
 1-14
 1 drop 0.1% soln. in water red 
 violet
Methyl violet
 0.2-3.0
 1-2 drops 0.1% soln. in water yellow
 violet
Thymol blue (1st range)
 1.2-2.8 1-2 drops 0.1% soln. in water red yellow
Tropeolin OO (Orange IV)
 1.3-3.2 1 drop 1% soln. in water red yellow
Benzopurpurin 4B
 1.2-4.0
 1 drop 1% soln. in water in 90% alc. violet
red
Methyl yellow
 2.9-4.0
 1 drop 0.1% soln. in water red
yellow
Methyl orange 3.1-4.4 1 drop 0.1% soln. in water red orange
Bromphenol blue 3.0-4.6 1 drop 0.1% soln. in water yellow purple
Congo red
 3.0-5.0
 1 drop 0.1% soln. in water blue 
 red
Bromocresol green 4.0-5.6 1 drop 0.1% soln. in water yellow blue-green
Methyl red 4.4-6.2 1 drop 0.1% soln. in water red yellow
Chlorophenol red
 5.4-6.8
 1 drop 0.1% soln. in water yellow
 red
Bromcresol purple
 5.2-6.8
 1 drop 0.1% soln. in water yellow
 purple
Andrade's acid fuchsin 5-8
 1 drop 0.1% soln. in water pink
 yellow
Litmus 4.5-8.3
 1 drop 0.1% soln. in water red
 blue
Bromthymol  blue 6.0-7.6 1 drop 0.1% soln. in water yellow blue
Phenol red 6.4-8.0 1 drop 0.1% soln. in water yellow red
Neutral red 6.8-8.0 1 drop 0.1% soln. in 70% alc. red yellow
Cresol red
 7.2-8.8
 1 drop 0.1% soln. in water yellow
 red
Thymol blue (2nd range)
 8.0-9.6 1-5 drops 0.1% soln. in water yellow blue
Phenolphthalein
 8.3-10.0 1 5 drops 0.1% soln. in 90% alc. colourless red
Thymolphthalein 9.3-10.5 1 drop 0.1% soln. in 90% alc. colourless blue
Alizarin yellow R
 10.2-12.0 1-5 drops 0.1% soln. in 90% alc. yellow red
Indigo carmine
 11.4-13.0
 1 drop 0.1% soln. in water blue 
 yellow
Tropeolin O
 11.0-13.0 1 drop 0.1% soln. in water yellow orange-brown
Nitramine 11.0 13.0 1-2 drops 0.10% soln. in 70% alc. colourless orange-brown
Trinitrobenzene 12.0-13.4 1 drop 0.1% soln. in water colourless orange
Thymol blue (1st range) / Thymol blue (2nd range) Indicator
pH 1.2 red to pH 2.8 yellow / Indicator, pH 8.0 yellow to pH 9.6 blue
Andrade's acid fuchsin indicator
Add 5 g of acid fuchsin to deionized water. Add 150 mL of M sodium hydroxide soln.. Mix the soln. and leave to stand for one day. The colour should change from from red to brown. If the soln. is not decolourized enough, add  10 mL of M sodium hydroxide soln.. Mix the soln. and leave to stand for one day. Repeat the process until the soln. has a straw-yellow colour.