lab6 chemis .docx - Introduction Beer-Lambert law in...

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Introduction Beer-Lambert law in spectroscopy, a relation concerning the absorption of radiant energy by an absorbing medium. It states that the absorptive capacity of a dissolved substance is directly proportional to its concentration in a solution. The relationship can be expressed as A = ε lc where A is absorbance, ε is the molar extinction coefficient (which depends on the nature of the chemical and the wavelength of the light used), l is the length of the path light must travel in the solution in centimetres, and c is the concentration of a given solution. Phenanthroline is a heterocyclic organic compound. It is a white solid that is soluble in organic solvents. It is used as a ligand in coordination chemistry for quantitative analysis studies and forms strong complexes with most metal ions. It forms a stable complex with Fe(II) ion called ferroin, which is used as an indicator in Fe(II) salt titrations. Ferroin is also used in the determination of other metals, such as nickel, ruthenium, and silver. Phenanthroline is synthesized by heating o-phenylenediamine or 8-aminoquinoline with glycerol, H2SO4, and nitrobenzene. In this experiment, the ferrous ammonium sulfate is mixed with hydroxylamine hydrochloride solution, sodium acetate solution and 1,10-phenanthroline solution to form iron phenanthroline complex. After that, the solution is dilute with deionised water. Spectrophotometer is used to scan the absorbance spectra of the different concentrations of iron phenanthroline complexes in different wavelengths. The aim for the experiment is to measure the absorbance of different concentrations of iron phenanthroline complex and to observe deviations to Beer’s law that occurs at higher concentrations. Materials Apparatus: 50ml volumetric flasks, 1.00-10.00 mL volumetric pipettes, graduated cylinders, pipettes, conical flasks, filter funnel, spectrophotometer, cuvette, tissue paper. Reagents: 2% hydroxylamine hydrochloride solution, 10% sodium acetate solution, 5 x 10-4 M solution of ferrous ammonium sulfate in 1% sulfuric acid, 0.002 M 1,10-phenanthroline solution, deionised water.
Methodology First, pipetted 2.5, 5, 7.5, 10ml of ferrous ammonium sulphate into four separate 50 mL volumetric flasks. Secondly, measure 5 mL of 2%(v/v) hydroxylamine hydrochloride solution by graduated cylinders and add the solution into all volumetric flasks. Thirdly, measure 10

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