Indicator — Science definition
Defined in 2 courses:
- A chemical, like litmus paper, that changes color depending on the pH of a solution. (Physical Science: Matter, Forces & Energy)
- A substance, such as litmus or phenolphthalein, that changes color depending on the pH of the solution it is added to. (Physical Science: Chemistry)
Where it is taught
- Acids, Bases & pH — Chemistry, Physical Science: Matter, Forces & Energy, Grade 8
- pH & Neutralization — Acids, Bases & Titration, Physical Science: Chemistry, Grade 11
In use
Use supplied records, labeled safe samples, and an appropriate indicator to study a solution rather than trying to identify an unknown substance by taste or smell.
Acids, Bases & pH
Litmus distinguishes broad acidic and basic behavior, while an appropriate indicator can help locate a titration endpoint.
pH & Neutralization
Questions using indicator
Problem 1
Answer and explanation
You dip the litmus paper into the solution; if it turns red, the solution is acidic, and if it turns blue, the solution is basic. The color change tells you the general pH range without needing a meter.
Problem 2
Answer and explanation
The 8–9 sample is basic and the pH 6 sample acidic under the stated common room-temperature aqueous convention. Indicator color supplies a range, not that exact decimal.
Use the supplied key and conditions.
Respect measurement resolution and the logarithmic scale.
The 8–9 sample is basic and the pH 6 sample acidic under the stated common room-temperature aqueous convention. Indicator color supplies a range, not that exact decimal.
Response criteria
- Use the named labels, directions or supplied quantities accurately.
- Connect the visual evidence to the scientific mechanism or calculation.
- State the relevant model conditions or limitation.
Problem 3
Answer and explanation
The 8–9 sample is basic and the pH 6 sample acidic under the stated common room-temperature aqueous convention. Indicator color supplies a range, not that exact decimal.
Use the supplied key and conditions.
Respect measurement resolution and the logarithmic scale.
The 8–9 sample is basic and the pH 6 sample acidic under the stated common room-temperature aqueous convention. Indicator color supplies a range, not that exact decimal.
Response criteria
- Use the named labels, directions or supplied quantities accurately.
- Connect the visual evidence to the scientific mechanism or calculation.
- State the relevant model conditions or limitation.
Problem 4
- changes the pH
- shows the pH by changing colour
- neutralises the solution
- measures temperature
Answer and explanation
shows the pH by changing colour
Indicators report pH through a colour change without altering what is being measured appreciably.