Final answer:
The excess iron's pale yellow color in the solution likely does not interfere substantially with the spectrophotometric measurement of the deep red iron thiocyanate complex, due to the low intensity of the yellow relative to the red.
Step-by-step explanation:
The presence of excess iron in a solution could potentially interfere with the measurement of iron thiocyanate concentration. However, in the context of the described laboratory exercise, this would likely not be the case if the pale yellow iron solution indicates the presence of Fe3+ in low concentration. Iron thiocyanate, Fe(SCN)2+, is known to form a deep red complex, and the measurement of its concentration is often based on the intensity of this red color in the solution.
The core of the problem lies in the fact that the color intensity and associated absorbance measurements used to determine the concentration of the Fe(SCN)2+ complex can be affected by the presence of other colored species in solution. Since the observed yellow color of the solution suggests there are only trace amounts of uncomplexed Fe3+, the effect on absorbance should be minimal. Therefore, the presence of excess unreacted Fe3+ shouldn't significantly interfere with spectrophotometric analysis, assuming the iron solution's inherent pale yellow color is much less intense than the red of the iron thiocyanate complex.