Observation: If you add a solution containing iron(III) ions (Fe³⁺) to a mixture of iron(III) and thiocyanate ions, the solution will become more intensely red.

Explanation:

* The Reaction: The reaction between iron(III) ions and thiocyanate ions (SCN⁻) forms a complex ion called hexathiocyanatoferrate(III), which has the formula [Fe(SCN)₆]³⁻. This complex is responsible for the red color.

* Equilibrium: The reaction is an equilibrium reaction, meaning it can proceed in both directions:

Fe³⁺(aq) + 6 SCN⁻(aq) ⇌ [Fe(SCN)₆]³⁻(aq)

* Le Chatelier's Principle: Adding more iron(III) ions to the mixture shifts the equilibrium to the right, favoring the formation of more of the red [Fe(SCN)₆]³⁻ complex. This is because the system tries to relieve the stress of the added iron(III) ions.

In summary: Adding more iron(III) ions to the mixture will cause the solution to become a deeper, more intense red because more of the red complex will be formed.