In the equilibrium reaction of FeSCN²⁺, the color change indicating a shift from orange at equilibrium can be described as follows:
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Initial Color at Equilibrium: The system is at equilibrium with the presence of FeSCN²⁺, which gives the solution an orange color.
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Forward Reaction (Addition of Fe³⁺): When Fe³⁺ ions are added to the solution, the equilibrium will shift to the right to produce more FeSCN²⁺. This increase in FeSCN²⁺ causes the solution to become more orange (more intense).
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Reverse Reaction (Removal of SCN⁻): If SCN⁻ is removed from the solution, the equilibrium will shift to the left, favoring the production of Fe³⁺ and SCN⁻ ions, which results in a decrease in the concentration of FeSCN²⁺. This shift will result in a color change from orange to a pale yellow as the red color of the iron thiocyanate complex diminishes.
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Removal of FeSCN²⁺: If FeSCN²⁺ itself is removed (by precipitation or another method), the same outcome will occur—the equilibrium shifts to the left leading to a pale yellow solution.
In summary:
- Addition of Fe³⁺: Solution becomes more intense orange.
- Removal of SCN⁻ or FeSCN²⁺: Solution shifts to pale yellow as the orange color decreases.