NAME: EDWARD AFUTU INDEX NO: 8030212 EXPERIMENT: I.2.2.2. DEMONSTRATOR: MISS NAOMI KABIRI DATE: 21-01-14
ANALYSIS OF COPPER IN BRASS BY UV – VISIBLE SPECTROSCOPY
To determine the percentage of copper in brass by UV-visible spectroscopy. INTRODUCTION
Electromagnetic radiation, of which ultraviolet and visible light are but two examples, has properties of both waves and particles. When light acts as a particle, called a photon, each light particle possesses a discrete amount of energy called a quantum. When a molecule is exposed to electromagnetic energy it can absorb a photon, increasing its energy by an amount equal to the energy of the photon. The energy of the absorbed photon can be calculated if the frequency, ν, (the symbol, ν, is a Greek letter, pronounced nu) of the light is known according to Equation 1.
E = hν Equation 1 Where h is a constant known as Planck’s constant after Max Planck, the German scientist who first proposed it. Planck’s constant has a value of 6.63 X 10-34 J. s . Frequency is measured in units of 1/s or Hertz (Hz). The frequency of a light wave is inversely proportional to its wavelength, λ, (λ is also Greek and is pronounced lambda) which is typically measured in meters. The product of ν and λ is the speed of light, c as shown in Equation 2. c has a value of 2.998 X 108m/s.
c = λν Equation 2 Molecules are highly selective in the wavelengths of light they can absorb. The photons absorbed depend on the on molecular structure and can be measured by instruments called spectrometers. The data obtained from a spectrometer are very sensitive indicators of molecular structure and concentration. UV-visible spectrophotometry (UV-VIS) uses only the ultraviolet and visible regions of the electromagnetic spectrum. UV light ranges from approximately 10 nm to about 400 nm. The visible region of the spectrum ranges from 400 nm to 700 nm. Red light lies at the low energy end of the visible spectrum and violet lies at the high energy end. UV-VIS spectroscopy depends on transitions of electrons in a molecule from one electronic energy level to another. It is used mostly in studying transition metal complexes and conjugated π systems in organic molecules. One of the principal uses of UV-VIS spectrometry is in determining the concentration of an absorbing (coloured) molecule. The amount of light absorbed, and thus the intensity of the colour of the solution , depends on the concentration of the absorbing species in the solution. UV-VIS absorption peaks are typically quite broad and are often spoken of as bands rather than as peaks. The wavelength at maximum absorption is referred to as λ max and is the optimal wavelength for a pure solution. For an impure solution, a “blank” solution can be prepared which contains all components of the solution except the one being analyzed. This solution is used to subtract out absorbance due to interfering species. When a beam of light with intensity, Io, passes through a solution, a coloured...
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