Determination of Iron in Natural Water by Spectrophotometry.

Topics: Electromagnetic spectrum, Spectroscopy, Light Pages: 5 (1654 words) Published: February 21, 2013
Title: Determination of Iron in Natural water by Spectrophotometry. Aim: To determine the iron in natural water by spectrophotometry. Abstract: The iron in natural water was determined by utilizing spectrophotometric analysis. That was done by measuring the absorbance of five Fe(oPH)2+3 standards at 510 nm. From that information, a calibration curve was plotted and used to find the amount of Fe2+ that was in two unknown water samples based on the absorbance readings obtained with them at 510nm. The equation of the line was found to be y=0.1765x + 0.0705. It was then determined that there was no iron present in water sample A, while for water sample B, the iron was present in the proportions of 0.9037ppm, 1.614x10-5M and 9.037x10-3%. Introduction: Spectroscopy is the study of the interaction of light or electromagnetic radiation with matter. Spectrophotometry is any technique that uses light to measure chemical concentrations. Electromagnetic radiation is a form of energy when reacted with matter, can be absorbed, reflected or refracted, and how EMR reacts with matter depends on the properties of the material, based on the frequency, wavelength, absorbance etc. The electromagnetic spectrum shows representative molecular processes that occur when light in each region is absorbed. The visible spectrum spans the wavelength range 380-780nm, so each region is absorbs at different wavelengths. The red-orange complex that forms between Iron (II) and 1,10-phenanthroline is useful for the determination of iron in water supplies. The reagent is a weak base that reacts to form phenanthrolinium ion in acidic media. The red-orange complex that forms between iron(II) and 1,10-phenanthroline (orthophenanthroline) is useful in determining iron in water supplies. The reagent is a weak base that reacts to form phenanthrolinium ion, phenH+, in acidic media. A commonly used method for the determination of trace amounts of iron involves the complexation of Fe2+ with 1,10-phenanthroline (phen) to produce an intensely red orange colored complex: Fe2+ + 3phen Fe(phen)32+. Since the iron present in the water predominantly exists as Fe3+, it is necessary to first reduce Fe3+ to Fe2+. This is accomplished by the addition of the reducing agent hydroxylamine. An excess of reducing agent is needed to maintain iron in the +2 state (because dissolved oxygen will reoxidize Fe2+ to Fe3+). Fe2+ is quantitatively complexed by 1,10-phenanthroline in the pH range from 3 to 9. Sodium acetate is used as a buffer to maintain a constant pH at 3.5. If the pH is too high, the Fe2+ will be oxidized to Fe3+; if the pH is too low, H+ will compete with Fe2+ for the basic 1,10-phenanthroline (to form phenH+). Either way, complete complexation won't be achieved. The determination of the iron-phen complex is performed with a spectrophotometer at a fixed wavelength of 510nm using external calibration based on iron standard solutions. In the spectrophotometer, light is passed through a monochromator (a prism, a grating, or even a filter) to select a range of wavelength and some of the light may be absorbed by the sample therefore giving the transmittance, which is the fraction of the original light that passes through the sample and has the range 0 to 1. Absorbance, sometimes called optical density, is the heart of spectrophotometry as applied to analytical chemistry Beer-Lambert's law, A=ebc , where the concentration of the sample, M, path length , cm, quantity (epsilon) is called the molar absorptivity. Molar absorptivity is the characteristic of a substance that tells how much light is absorbed at a particular wavelength. Both a and e depend on the wavelength of electromagnetic radiation. Attenuation of radiation as it passes through the sample leads to a transmittance of less than 1. Besides absorption by the analyte, several additional phenomena contribute to the net attenuation of radiation, including reflection and absorption by the sample container, absorption...
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