Overview
This lecture discusses the reaction between iron(III) ions and thiocyanate ions, focusing on the resulting equilibrium, properties, and significance of the formed complex.
Iron(III) and Thiocyanate Reaction
- Iron(III) ions (Fe³⁺) react with thiocyanate ions (SCN⁻) to form a blood-red complex ion.
- The key reaction: Fe³⁺(aq) + SCN⁻(aq) ⇌ [Fe(SCN)]²⁺(aq).
- The reaction is rapid and reaches equilibrium quickly in aqueous solution.
- The blood-red color indicates the presence of the [Fe(SCN)]²⁺ complex.
Chemical Equilibrium Concepts
- The reaction demonstrates dynamic equilibrium: forward and reverse reactions occur at the same rate.
- Le Châtelier's Principle applies; adding Fe³⁺ or SCN⁻ increases product formation ([Fe(SCN)]²⁺).
- Removing products or reactants shifts the equilibrium to maintain balance.
Applications and Uses
- The intense color is useful for qualitative and quantitative analysis of iron or thiocyanate ions.
- This reaction is commonly used in laboratory experiments to study equilibrium and colorimetry.
Key Terms & Definitions
- Iron(III) ion (Fe³⁺) — a metal ion with a +3 charge, also called ferric ion.
- Thiocyanate ion (SCN⁻) — a negatively charged ion made of sulfur, carbon, and nitrogen.
- [Fe(SCN)]²⁺ complex — a blood-red ion formed from iron(III) and thiocyanate.
- Dynamic equilibrium — a state where the rate of the forward reaction equals the rate of the reverse reaction.
- Le Châtelier's Principle — if a system at equilibrium is disturbed, it shifts to reduce the disturbance.
Action Items / Next Steps
- Review the reaction equation and identify components of the equilibrium.
- Practice applying Le Châtelier's Principle to predict changes in the system.
- Prepare for a lab experiment on iron(III)-thiocyanate equilibrium if assigned.