Acid-base indicators

Definition

Acid-base indicators are substances that change color in response to changes in pH, allowing the determination of the acidic or basic nature of a solution. They are commonly used in titrations to signal the endpoint of a reaction.

5 Must Know Facts For Your Next Test

1. Acid-base indicators have a specific pH range over which they change color.
2. Common examples include litmus, phenolphthalein, and bromothymol blue.
3. The choice of indicator depends on the expected pH at the titration's equivalence point.
4. Indicators function due to their different ionic forms having different colors.
5. Phenolphthalein is colorless in acidic solutions and pink in basic solutions.

Review Questions

• What role do acid-base indicators play in titrations?
• Why is it important to choose an appropriate indicator for a specific titration?
• How does phenolphthalein indicate the presence of a base?

Related terms

pH:

A measure of the acidity or basicity of an aqueous solution, defined as the negative logarithm of the hydrogen ion concentration.

Titration:

A laboratory method used to determine the concentration of an analyte by reacting it with a standard solution.

Equivalence Point:

The point in a titration at which the amount of titrant added is exactly enough to completely neutralize or react with the analyte.