Expt9

Spectrophotometric Determination of Iron in Aqueous Solutions as a Complex of 1,10-Phenanthroline

Zalameda, Jencis Franz M.,

Department of Mining, Metallurgical, and Materials Engineering, College of Engineering

University of the Philippines, Diliman, Quezon City, Philippines

Date Performed: October 30, 2014

Date Submitted: November 6, 2014

Answers to Questions

The concentration of iron in solutions as a complex of 1,10-phenantroline is determined through spectrophotometry. A double beam spectrophotometer, which compares the light intensity between two light paths, one path containing a reference sample and the other the test sample, is used. The concentration is determined by using Beer-Lambert law which presents the linear relationship between the absorbance and concentration of the substance, expressed as:

A=abc (1)

where A is absorbance

A is the molar absorbtivity, L mol-1 cm-1

b is the path length of the sample, cm

c is the concentration, mol L-1

It is easier that Beer’s law be expressed in absorbance rather than transmittance since when graphed, it presents a linear relationship with the concentration as opposed to transmittance having a curved graph since T=e-ebc.

Beer’s law also has limitations. If the concentration of the analyte is high, the analyte begins to behave differently due to interactions with the solvent and other solute molecules and at times even due to hydrogen bonding interactions. Also at high concentrations, there are changes in refractive index and shift in chemical equilibria therefore low concentrations are preferred when using Beer’s law.

The concept of spectral scanning or the measurement of absorbance in a range of visible wavelengths is also used. It is significant since it determines the peak wavelength where the solution has the highest absorbance and stable. Analytical measurements are made using light in this wavelength will minimize deviations from Beer’s Law. Also, it can help you...