Introduction:
Each chemical reaction has a typical condition of equilibrium at a specified temperature. If two reactants are mixed, then they react to form products till a state is reached where the quantities of reactants and products will remain the same. At this position, the reactants and products are to be said in chemical equilibrium and will remain the same, till the system is changed somehow. This condition is known as equilibrium state and it is associated with a number called the equilibrium constant, Keq which is the expression of the necessary condition particularly the concentrations of reactants and products for a specific reaction at a given temperature.
In this experiment, I studied the equilibrium properties of the reaction between the iron(III) ion and thiocyanic acid (HSCN). The equilibrium involving iron (III) ion and thiocyanic acid is shown below:
FeÂ³+ (aq) + HSCN (aq) <--> FeSCNÂ²+ (aq) + H+ (aq)

According to the general law, Keq for this reaction is given from the blow formula involving the concentrations of all components.

After mixing the solution of Fe3+ and HSCN, a deep red FeSCN2+ complex ion is formed. The intensity of the color of the solution is directly related to the concentration of FeSCN2+ complex, which can be estimated using a spectrophotometer. Beerâ€™s Law is very useful and applicable in spectrophotometry which relates the absorbance with the concentration of the solution. A straight-line relationship observed in a dilute solution between the color intensity (measured as Absorbance) and the concentration of colored complex FeSCN2+. Beerâ€™s law is expressed as follows:
A = É›bC
Here;
A = absorbance
É› = molar absorptivity coefficient
b = cell path length (in cm)
C = concentration of the colored substance
For the purpose of this experiment, the inference of Beerâ€™s Law is that the concentration of the red complex ion FeSCN2+ in solution will be proportional to the absorbance of the given solution.
In the first part of this experiment, a very small amount of HSCN was converted completely to the colored FeSCN2+ complex ions by means of the addition of an excessive amount of Fe3+ ions. By applying the Le ChÃ¢telierâ€™s principle it can be assumed that the equilibrium will shift strongly to the right converting virtually all the initial HSCN to the FeSCN2+ ion. Both the Fe3+ and HSCN solutions were prepared using 0.50 M HNO3 in order to maintain a sufficient H+ ion concentration to prevent the formation

Question.3 b. The Hertzsprung-Russell (HR) diagram shown in Figure...