When the pH of a solution containing dichromate ions (Cr₂O₇²⁻) is raised, the following happens:

Dichromate ions (Cr₂O₇²⁻) are converted to chromate ions (CrO₄²⁻).

Here's the chemical reaction:

Cr₂O₇²⁻ + H₂O ⇌ 2CrO₄²⁻ + 2H⁺

This reaction is an equilibrium reaction, and the position of equilibrium shifts towards the right (favoring chromate ions) when the pH is raised.

Here's why:

* pH and H⁺ concentration: As the pH increases, the concentration of H⁺ ions decreases.

* Le Chatelier's Principle: The equilibrium shifts to relieve the stress caused by the decrease in H⁺ concentration. To do this, the reaction consumes H⁺ ions, shifting the equilibrium to the right, producing more chromate ions.

Result:

* The solution will change color. Dichromate ions are orange, while chromate ions are yellow. As the pH rises, the solution will become more yellow.

Other important considerations:

* Equilibrium constant: The equilibrium constant for this reaction is about 3.2 x 10⁻¹⁴, indicating that the reaction strongly favors dichromate ions in acidic solutions.

* Reversibility: The reaction is reversible. If the pH is lowered again, the reaction will shift back to the left, favoring dichromate ions.

Practical applications:

* This reaction is used in analytical chemistry to determine the concentration of chromate or dichromate ions.

* The color change can also be used as an indicator in titrations.

Let me know if you have any other questions!