chemistry

Topics: Spectroscopy, Electromagnetic radiation, Light Pages: 5 (2781 words) Published: November 1, 2014

OBJECTIVES:
To determine the maximum wavelength of potassium permanganate. To plot the calibration curve of potassium permanganate.
To determine the concentration of an unknown solution of potassium permanganate. INTRODUCTION:
UV Spectrophotometer has 4 main components which is the UV light source, the sample, detector and the processor/recorder. Spectrophotometry is a technique that uses the absorbance of light by an analyte (the substance to be analyzed) at a certain wavelength to determine the analyte concentration. Useful wavelengths for spectrophotometry range from 185 to 3,000 nm. Spectroscopy is one of the most powerful analytical techniques in modern science. Spectroscopy works by correlating the concentration of a species in solution to the amount of light it absorbs. It included the observations of absorption or emission of electromagnetic radiation resulting from transitions of atoms or molecules from one energy level to other level. The spectrophotometer measures how much light is absorbed at a given wavelength. When an atom or molecule absorbs energy, electrons are promoted from their ground state to an excited state. When a molecule at a ground state absorbs energy, it called transition to a higher energy state.The higher energy state can be said as excited state. In a molecule, the atoms can rotate and vibrate with respect to each other. These vibrations and rotations also have discrete energy levels, which can be considered as being packed on top of each electronic level. UV/Vis spectroscopy is routinely used in analytical chemistry for thequantitative determination of different analytes, such as transition metal ions, highly conjugated organic compounds, and biological macromolecules. Spectroscopic analysis is commonly carried out in solutions but solids and gases may also be studied. Solutions of transition metal ions can be colored (absorb visible light) because the electrons within the metal atoms can be excited from one electronic state to another. The color of metal ion solutions is strongly affected by the presence of other species. The Beer-Lambert law states that the absorbance of a solution is directly proportional to the concentration of the absorbing species in the solution and the path length. Thus, for a fixed path length, UV/Vis spectroscopy can be used to determine the concentration of the absorber in a solution. It is necessary to know how quickly the absorbance changes with concentration.

The diagrams of the components of a typical spectrometer are shown in the following diagram. The functioning of this instrument is relatively straightforward. A beam of light from a visible and/or UV light source (colored red) is separated into its component wavelengths by a prism or diffraction grating. Each monochromatic (single wavelength) beam in turn is split into two equal intensity beams by a half-mirrored device. One beam, the sample beam (colored magenta), passes through a small transparent container (cuvette) containing a solution of the compound being studied in a transparent solvent. The other beam, the reference (colored blue), passes through an identical cuvette containing only the solvent. The intensities of these light beams are then measured by electronic detectors and compared. The intensity of the reference beam, which should have suffered little or no light absorption, is defined as I0. The intensity of the sample beam is defined as I. Over a short period of time, the spectrometer automatically scans all the component wavelengths in the manner described. The ultraviolet (UV) region scanned is normally from 200 to 400 nm, and the visible portion is from 400 to 800 nm. Moreover, If the sample compound does not absorb light of a given wavelength, I = I0. However, if the sample compound absorbs light then I is less than I0, and this difference may be plotted on a graph versus wavelength, as shown on the right. Absorption may be presented as transmittance (T = I/I0) or absorbance (A=...

References: S:
Harris, Daniel C. Sixth Edition Quantitative Chemical Analysis. Pg. 408-409. New York: W.H. Freeman and Company, 2003.
Raymond C. Tenth Edition CHEMISTRY. Pg. 147-149. New York: McGraw-Hill and Company, 2010.
Continue Reading

Please join StudyMode to read the full document

You May Also Find These Documents Helpful

  • Chemistry Essay
  • Chemistry and Molecular Ion Peak Essay
  • Chemistry Projects Essay
  • Essay about Chemistry Gr 9 & 10 Review
  • organic chemistry Essay
  • Chemistry Formula Essay
  • Chemistry (Redox) Essay
  • Sample Paper Chemistry

Become a StudyMode Member

Sign Up - It's Free