Formal Report for Experiment 14

Topics: Electromagnetic radiation, Light, Spectroscopy Pages: 9 (2879 words) Published: December 11, 2011
Experiment#14: Spectroscopy of Cobalt II Ion
The purpose of the experiment was to preparation of a standard solution, quantitative dilutions, and use of a spectrometer to determine an absorption spectrum and a Beer’s law plots.
In the learning object of light, we know about the structure of atoms and molecules come from learning our interaction with light. The light may be considered to have both wave nature and particle nature. A photon is the basic unit of light that demonstrates both of these properties. Which have the equation, speed of a wave to its wavelength and frequency, V= C/λ (λ is wavelength, V is frequency, C is speed of light c=3.00x108 m/s). Also, energy of a photon to the frequency, ∆E=hv (E is energy, v is frequency, h is a constant factor h=6.63x10-34 J.S)

As we can see light at night by neon light or the firework in the sky that is being released by atoms in them. We can learn about how light interacts with atoms and understand the arrangement and behavior of electrons in atoms. Structure of atoms and molecules are described in the scientific literature and based sound experimental evidence. The most compelling evidence for structure comes from spectroscopic experiments, as will be demonstrated in this paper. Spectroscopy is one of technique, which uses the interaction of energy with a sample to perform an analysis. Spectrometer produces light of a specific wavelength. Light bulbs produce white light with all colors 400-700nm. Diffraction grating splits white light into different wavelength. The slip allows only narrow bond of light, which is wavelength. Photometer detector measures intensity of light passing through the sample. Also, spectrophotometry measure the amount of light is absorbed material.

Amount of light absorbed is not dependent on wavelength and use one wavelength at a time. Monochromatic light is light made of photons of only one wavelength λ. Wavelength at which greatest absorbance occurs is different for each species. When we correlate absorbance to concentration, we use wavelength maximum to give the most accurate results. We have equation to help us to find the wavelength maximum (λmax). They measure the absorbance of a sample at each wavelength by using a blank to set zero first. Then they find wavelength with the highest absorbance.

Beer’s Law equation: A=εbc (A is absorption, c is concentration (mole/l) or molarity of the absorbing species, b is path length of light through a sample, and ε is a constant which is found by the nature of the absorbing species).

When graphing the absorption and concentration, students calculate the slope of the graph. They use standard samples to make the graph and use the graph to determine the concentration of unknown sample. Then they can find the constant ε by knowing absorption, the path length, and the concentration).

Spectroscopy of Cobalt (II) ion is one of the experiments that they do in the laboratory. Preparing a standard solution, quantitative dilutions, and using a spectrometer to determine the absorption spectrum and a Beer’s la plot in the experiment did this. Indeed, in this experiment students will use the spectrometer to find absorption and concentration of five different amount Cobalt (II) solutions with different wavelength and different volume, and used this determine to concentration of the cobalt (II) solution ion in the unknown. Besides, other purpose of this experiment was to experience stoichiometric calculations. The students will learn how to calculate molarity of Co(NO3)2 will be determine from finding mass of beaker, mass of Co(NO3)2.6H2O, and mole of Co(NO3)2.6H2O. Material and Methods:

The experimental procedure consisted of three parts: preparation of the solutions absorption spectrum, Beer’s law plot, and determination of the concentration of the cobalt (II) ion in the unknown A. the detailed experimental procedure can be found in the primary reference of experiment, Murov, S.L. Experiments...
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