Which Can Act as a Self-Indicator?

Substances with strong inherent colors that change during chemical reactions can act as self-indicators, including KMnO₄, iodine, and dichromate salts.

Requirements for Self-Indication:

1. Distinct, visible color in solution
2. Color change occurs during the reaction
3. Color change coincides with equivalence point
4. No interference with reaction chemistry

Common Self-Indicators:

Oxidizing Agents:

• KMnO₄ (purple → colorless)
• K₂Cr₂O₇ (orange)
• I₂ (brown/yellow)

Why These Work: Their colored ionic forms (MnO₄⁻, Cr₂O₇²⁻, I₂) are reduced to colorless or differently colored products, providing a natural visual endpoint.

Key Takeaways:

• Must have strong, reaction-dependent color
• Color change = chemical change at endpoint
• Primarily redox-active species
• Eliminates need for external indicators