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The Fe(SCN)²⁺/ Fe(SCN)²⁺ Equilibrium

Last updated

Feb 22, 2023
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- The Electrolysis of Water
- The Fe(SCN)²⁺/ Fe(SCN)²⁺ Equilibrium - Expanded Version

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Chemical Concepts Demonstrated

Equilibrium
LeChatelier's Principle

Demonstration

Four beakers are filled with DI water. HNO₃, FeCl₃, and NH₄SCN are added to each of the beakers.

FeCl₃ is added to the first beaker.
NH₄SCN is added to the second beaker.
NH₄Cl is added to the third.
KNO₃ is added to the fourth.

Observations

At first, the beakers have a light red color.

1. When the FeCl₃ is added to the first beaker, the solution turns a deep red.
2. When the NH₄SCN is added to the second beaker, the solution also turns a deep red.
3. When the NH₄Cl is added to the third beaker, the color of the solution lightens.
4. When the KNO₃ is added to the fourth beaker, the color of the solution will also lighten , but not as much as with the NH₄Cl.

Explanations (including important chemical equations)

The initial light red color indicates the presence of the Fe(SCN)²⁺/Fe(SCN)₂⁺ complexes. The addition of more Fe³⁺and SCN^- causes the equilibrium to shift in favor of the products and more of the complex is formed, turning the solution to a deeper red (this indicates that free SCN^- and Fe³⁺ ions were present in the solution). The addition of more NH₄Cl shifts the equilibrium away from the complex towards the reactants to lighten the color of the solution. This is because the Cl^- ions sequester some of the Fe³⁺ ions. The increased ionic strength also helps to shift the equilibrium to the left.

The KNO₃ also lightens the color, but not as much as the the NH₄Cl. The ionic strength increase helps to lighten the color, but the lack of Cl^- ions hinders the process.

Contributors

Dr. George Bodner (Perdue University)

Chemical Concepts Demonstrated

Demonstration

Observations

Explanations (including important chemical equations)

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