Acid-base indicators

Acid-base indicators are compounds that change their color depending on the pH of the solution they are in. This property makes them extremely useful in chemistry for determining whether a solution is acidic or basic. Here are some common acid-base indicators along with their color changes:

1. Litmus:

- Red in acidic solutions.

- Blue in alkaline solutions.

2. Phenolphthalein:

- Colorless in acidic and neutral solutions.

- Pink to purple in alkaline solutions (effective pH range: 8.2 - 10).

3. Methyl Orange:

- Red in acidic solutions (pH < 3.1).

- Yellow in alkaline solutions (pH > 4.4).

4. Bromothymol Blue:

- Yellow in acidic solutions (pH < 6).

- Blue in alkaline solutions (pH > 7.6).

5. Phenol Red:

- Yellow in acidic solutions (pH < 6.8).

- Red in alkaline solutions (pH > 8.4).

6. Universal Indicator:

- Provides a full spectrum of colors for different pH levels, ranging from red (strongly acidic) to violet (strongly alkaline).

7. Thymol Blue:

- Yellow in acidic solutions (first transition pH < 1.2).

- Blue in alkaline solutions (second transition pH > 9.6).

8. Bromocresol Green:

- Yellow in acidic solutions (pH < 3.8).

- Blue in alkaline solutions (pH > 5.4).

9. Alizarin Yellow R:

- Yellow in acidic solutions.

- Red in alkaline solutions (effective pH range: 10.1 - 12.0).

10. Congo Red:

• Blue in acidic solutions.

Red in alkaline solutions (effective pH range: 3.0 - 5.0)

Each of these indicators has its specific pH range where it changes color, making them useful for different types of acid-base titrations and pH estimations in various chemical and educational settings.