Titrations and Color Changes

Introduction

• Demonstration of color changes in titrations.
• Importance of initial solutions in the conical flask and burette.
• Chemicals used: Hydrochloric acid (acid), Sodium hydroxide (base/alkali).
• Indicators used: Phenolphthalein, Methyl orange.

Setup

• 25 mL of acid and base measured into conical flasks.
• Two setups: one for each indicator.
• Burettes: one containing HCl, the other containing NaOH.

Procedure

Using Phenolphthalein

Base in Conical Flask

• Starting point: Sodium hydroxide (base) in the conical flask.
• Indicator addition: Few drops of phenolphthalein (pink in alkali).
• Initial color: Pink.
• Process: Add HCl from the burette into the conical flask.
• Observation: Color changes from pink to colorless.
• Conclusion: Phenolphthalein color change (base to acid) goes from pink to colorless.

Acid in Conical Flask

• Starting point: Hydrochloric acid in the conical flask.
• Indicator addition: Few drops of phenolphthalein.
• Initial color: Colorless (phenolphthalein colorless in acid).
• Process: Add NaOH from the burette into the conical flask.
• Observation: Color remains colorless initially, then turns pink upon sufficient base addition.
• Conclusion: Phenolphthalein color change (acid to base) goes from colorless to pink.

Using Methyl Orange

Base in Conical Flask

• Starting point: Sodium hydroxide in the conical flask.
• Indicator addition: Few drops of methyl orange (yellow in alkali).
• Initial color: Yellow.
• Process: Add HCl from the burette into the conical flask.
• Observation: Color changes from yellow to red (can appear pinkish).
• Conclusion: Methyl orange color change (base to acid) goes from yellow to red.

Acid in Conical Flask

• Starting point: Hydrochloric acid in the conical flask.
• Indicator addition: Few drops of methyl orange (red in acid).
• Initial color: Red.
• Process: Add NaOH from the burette into the conical flask.
• Observation: Color changes from red to yellow upon sufficient base addition.
• Conclusion: Methyl orange color change (acid to base) goes from red to yellow.

Summary

• The initial solution in the conical flask and the type of indicator used determine the observed color change during titration.
• Phenolphthalein: Pink in base to colorless in acid, and colorless in acid to pink in base.
• Methyl Orange: Yellow in base to red in acid, and red in acid to yellow in base.