Common Indicators

The Acidic Environment‎ > 1. Indicators‎ > ‎

Identify that indicators such as litmus, phenolphthalein, methyl orange and bromothymol blue can be used to determine the acidic or basic nature of a material over a range, and that the range is identified by change in indicator colour

Identify data and choose resources to gather information about the colour changes of a range of indicators

  • Indicator: A chemical that change colour as the concentration of hydrogen ions in a solution changes.
  • Indicator range: The range of acidity or basicity over which the colour of an indicator changes colour.
  • Indicators can be either natural (extracted from plants) or synthetic.
  • Common indicators include:
    • Litmus: A dye extracted from various species of lichen that changes colour around the neutral range.
    • Phenolphthalein: A synthetic indicator that changes colour in the basic range.
    • Methyl orange: A synthetic indicator that changes colour in the acidic range.
    • Bromothymol blue: A synthetic indicator than changes colour around the neutral range.
Highly acidic
Slightly acidic
Slightly basic
Highly basic
Methyl orangeRedYellow
Bromothymol blueYellowGreenBlue
Colours and approximate ranges of common indicators


Various pH indicators


IndicatorLow pH colorTransition pH rangeHigh pH color
Gentian violet (Methyl violet)yellow0.0–2.0blue-violet
Leucomalachite green (first transition)yellow0.0–2.0green
Leucomalachite green (second transition)green11.6–14colorless
Thymol blue (first transition)red1.2–2.8yellow
Thymol blue (second transition)yellow8.0–9.6blue
Methyl yellowred2.9–4.0yellow
Bromophenol blueyellow3.0–4.6purple
Congo redblue-violet3.0–5.0red
Methyl orangered3.1–4.4orange
Bromocresol greenyellow3.8–5.4blue-green
Methyl redred4.4–6.2yellow
Methyl red / Bromocresol greenred4.5–5.2green
Bromocresol purpleyellow5.2–6.8purple
Bromothymol blueyellow6.0–7.6blue
Phenol redyellow6.8–8.4red
Neutral redred6.8–8.0yellow
Naphtholphthaleincolourless to reddish7.3–8.7greenish to blue
Cresol Redyellow7.2–8.8reddish-purple
Alizarine Yellow Ryellow10.2–12.0red

The colour changes and ranges of a wide range of indicators
From Wikipedia