Factors Affecting the Equilibrium Reaction of Iron (III) and Thiocyanate ions

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Factors Affecting the Equilibrium Reaction of Iron (III) and Thiocyanate ions

Research Question

How does the change in temperature of Iron (III) Thiocyanatoiron, containing iron (III) ions Fe3+ (aq) and thiocyanate ions SCN¬¬- (aq), affect the absorbance of the solution?

- Temperature at 25 °C, 30 °C, 35 °C, 40 °C, 45 °C, 50 °C, 55 °C, and 60 °C (equilibrate the Iron (III) Thiocyanatoiron (aq) in various temperatures using a digital water bath, and temperature checked using a digital thermometer connected to a data logger)

- Production rate of thiocynate ion measured by the degree of change in color using a colorimeter after 600 seconds since the reactants are mixed.

- The quantitative data of the absorbance of the solution will allow the determination of the concentration of the Iron (III) Thiocyanatoiron using the Beer–Lambert Law. The difference in concentration of the solution per temperature point provides the precise effect of temperature on the reaction’s equilibrium position.


This experiment investigates how changing a factor that affects the equilibrium reaction, in this case temperature, affects the equilibrium position.

Fe 3+ (aq) + S︎CN – (aq) ⇌ Fe ( SCN ) 2+ (aq) ( ∆H = - ve )

Pale Yellow Colorless Blood Red

This experiment uses Iron (III) ion and thiocyanate ion; the two chemicals are yellow colored and colorless, respectively. The product of the forward reaction is Iron (III) Thiocyanatoiron, which has a blood red color.

Dynamic equilibrium is when the macroscopic properties of the reaction are in constant at a specific temperature when the rate of the forward reaction is equal to that of the reverse reaction in a closed system. (Derry, Connor & Jordan, 2009)

Le Chatelier's Principle states that the change in temperature, pressure, or concentration will cause a shift in the reversible. (Derry, Connor & Jordan, 2009) Temperature, pressure, and concentration of a chemical are factors that may cause a shift in equilibrium position; the shift is to compensate the changes made by one of the three factors.

Since the forward reaction is exothermic, the increase in temperature increases the rate of the reversed reaction, meaning more Fe 3+ (aq) and S︎CN – (aq) will be formed, thus shifting the equilibrium position to the left, so the solution will be in yellow.
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