How does the colour of K₂Cr₂O₇ solution depend on pH of solution?

The color of a potassium dichromate (K₂Cr₂O₇) solution is influenced by the pH level of the solution due to the chemical equilibrium between different chromium species.

Color Changes with pH

In acidic conditions, K₂Cr₂O₇ appears orange due to the presence of the dichromate ion (Cr₂O₇²⁻). As the pH increases and the solution becomes more basic, the color shifts to yellow, primarily because of the formation of chromate ions (CrO₄²⁻).

Key Points to Remember

• Acidic Solution: Orange color from dichromate ions.
• Neutral to Basic Solution: Yellow color from chromate ions.
• pH Transition: The color change occurs as the pH crosses around 6 to 7.

Why This Happens

The transformation between dichromate and chromate ions is a result of protonation and deprotonation reactions. In acidic conditions, the equilibrium favors dichromate, while in basic conditions, chromate is favored.

Practical Implications

This pH-dependent color change is useful in various applications, including titrations and analytical chemistry, where visual indicators are essential for determining the acidity or basicity of a solution.