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.
Various pH indicators
|Indicator||Low pH color||Transition pH range||High pH color|
|Gentian violet (Methyl violet)||yellow||0.0–2.0||blue-violet|
|Leucomalachite green (first transition)||yellow||0.0–2.0||green|
|Leucomalachite green (second transition)||green||11.6–14||colorless|
|Thymol blue (first transition)||red||1.2–2.8||yellow|
|Thymol blue (second transition)||yellow||8.0–9.6||blue|
|Methyl red / Bromocresol green||red||4.5–5.2||green|
|Naphtholphthalein||colourless to reddish||7.3–8.7||greenish to blue|
|Alizarine Yellow R||yellow||10.2–12.0||red|
The colour changes and ranges of a wide range of indicators