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a student accidentally switches the set of KSCN and Fe(NO3)3/HNO3 solutions between part 1 and part...

a student accidentally switches the set of KSCN and Fe(NO3)3/HNO3 solutions between part 1 and part 2 so that there is excess of Iron(III) in Part II (equilibrium solutions) instead of in Part I (standard solutions). Will his standard curve equation describe accurately the relation between the absorbance and the colored complex? Will the equilibrium constants be reliable? Rationalize your answers.

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Answer #1

The reaction is

Fe+3 (aq) + SCN- (aq) = Fe(SCN)+2 (aq)

If there is excess Fe(NO3)3, then some of Fe+3 remains unreacted in the equilibrium but complex formation happens. We measure the absorbance and concentration of the complex in the solution. There is no change in the standard curve equation.

Equilibrium constant = [Fe(SCN)+2 ]/ [Fe+3 ] *[SCN- ]

The equilibrium constant is reliable as it is the ratio of product concentration and reactant concentration.

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