Observations of the initial solutions and the mixture of the two solutions can be seen in Table 1.

Observations of the equilibrium mixtures upon addition of various reagents can be seen in Table 2.

Observation when the temperature is changed: In test tube 7, the solution turns more orange in color (less red, more yellow) when heated.

In test tubes 1 and 2, when iron(III) nitrate, which contains a reactant, was added to the equilibrium solution, the red color of the solution intensified. This observation indicates that the equilibrium shifted to the right as concentration of the product, iron(III) thiocyanate ion, increased. Similarly, when potassium thiocyanate, which contains the other reactant, was added to the equilibrium solution, the red color of the solution intensified. This observation also indicates that the equilibrium shifted to the right as concentration of the product increased.

In test tubes 3 and 4, when silver nitrate (AgNO₃) was added to the equilibrium solution, the red color of the product faded and the solution became colorless. This observation indicates that the equilibrium shifted to the left as the concentration of reactants increased. In addition, a precipitate was observed. The red color reappeared upon addition of thiocyanate ion (SCN^-). This observation indicates that the equilibrium shifted to the right as the concentration of the product increased. The red color did not reappear when iron(III) ion (Fe³⁺) was added.

From these observations, it can be concluded that silver thiocyanate (AgSCN) was the precipitate that formed when silver nitrate was added to the equilibrium solution. The formation of this solid is responsible for the cloudiness observed in both test tubes. When the thiocyanate ion was removed from the solution by precipitation, the equilibrium shifted to the left, because the concentration of one of the reactants had been reduced. When more thiocyanate ion was then added, the equilibrium shifted back to the right to re-establish the equilibrium ratio of concentrations by re-forming iron(III) thiocyanate. The addition of more iron(III) ion did not shift the equilibrium back to the right, because the thiocyanate ion had been removed from the solution as silver thiocyanate precipitate and was no longer available to react with iron(III) to form the iron(III) thiocyanate ion.

In test tubes 5 and 6, when potassium phosphate ion (K₃PO₄) was added to the equilibrium solution, the red color of the products faded and the solution became yellow. This observation indicates that the equilibrium shifted to the left as the concentration of reactants increased. The red color reappeared upon addition of iron(III) ion (Fe³⁺). This observation indicates that the equilibrium shifted to the right as the concentration of the product increased. In addition, a precipitate was observed. The red color did not reappear when the thiocyanate ion (SCN^-) was added.

From these observations, it can be concluded that iron(III) phosphate (FePO₄) salt was formed when potassium phosphate was added to the equilibrium solution. When the iron(III) ion was removed from the solution by formation of this salt, the equilibrium shifted to the left, because the concentration of one of the reactants had been reduced. When more iron(III) ion was then added, the equilibrium shifted back to the right to re-establish the equilibrium ratio of concentrations by re-forming iron(III) thiocyante. Although no cloudiness was detected by eyesight when the phosphate ion was initially added, a cloudiness did appear when the iron(III) ion was subsequently added, which is the solid iron(III) phosphate salt. The addition of more thiocyanate ion did not shift the equilibrium back to the right, because the iron(III) ion had been removed from the solution as iron(III) phosphate salt and was no longer available to react with the thiocyanate ion to form the iron(III) thiocyanate ion.

In test tube 7, as the temperature increased, the red color of the products faded, indicating an equilibrium shift to the left as more reactants were formed. This observation leads to the conclusion that the reaction is exothermic. For an exothermic reaction, the heat generated by the reaction resides on the product side of the equation:

Fe³⁺ + SCN^- FeSCN²⁺ + heat

When heat was added to the system (by increasing the temperature), the equilibrium shifted to the left.

Table 1. Observations of the initial solutions and the mixture of the two solutions.

Table 2. Observations of the equilibrium mixtures upon addition of various reagents.