Indicators and Precautions in Volumetric Analysis

Indicators  

- Definition: Indicators are organic compounds, usually weak acids or bases, that change color according to the pH of the medium.  

- Application: Widely used in titration experiments to signal the endpoint of a reaction.  

Examples of Indicators:  

- Phenolphthalein  

- Methyl Orange  

- Methyl Red  

- Methyl Violet  

- Methylene Blue  

- Bromothymol Blue  

- Bromocresol Green  

- Thymol Blue  

- Litmus  

Precautions in Volumetric Analysis  

To ensure accuracy and reliability in titration experiments, the following precautions must be observed:  

1. Preparation of Apparatus  

   - Rinse burette with distilled water, then with the acid it will contain.  

   - Rinse pipette with distilled water, then with the base it will contain.  

   - Rinse conical flasks and beakers with distilled water.  

   - Ensure the burette is not leaking.  

2. Measurement Accuracy  

   - Take burette and pipette readings at eye level to avoid parallax error.  

   - Record values to two decimal places.  

3. Indicator Use  

   - Add only 2–3 drops of indicator to the base before titration.  

   - Do not leave the funnel on the burette during titration.  

4. Handling Pipette  

   - Do not blow out the last drop of liquid.  

   - Instead, touch the tip of the pipette to the wall of the conical flask to release it.  

5. Calculation and Accuracy  

   - Use the average volume of acid for calculations.  

   - Avoid air bubbles when filling the pipette or burette.