The experimental approach exploits Beer's Law, which predicts a linear relationship between the absorbance of the solution and the concentration of the analyte (assuming all other experimental parameters do not vary). The absorbance of the unknown solution, A u , is then used with the slope and intercept from the calibration curve to calculate the concentration of the unknown solution, c u .
The spectrum itself is a plot of absorbance vs wavelength and is characterized by the wavelength (λ max ) at which the absorbance is the greatest. Use the intensity of the transmitted light to calculate the absorbance of the sample at that wavelength. (For a blank, the intensity of the transmitted light is 300.0 photons/sec.) For a blank, the intensity of the transmitted light is 300.0 photons/sec. (Not all of the photons are shown in the simulation.)
Watch the motion of the photons and observe how some of the photons are absorbed (removed) as the beam of light passes through the cell containing the sample solution. The remainder of the light, 1 - T, is the fraction of the light absorbed by the sample. (Do not confuse the transmittance with the temperature, which often is given the symbol T.)
Each simulation will be performed using a different cell path length to isolate the effect of the cell path length on the absorption of light. Your goal is to answer the following questions: How does the cell path length affect the intensity of light reaching the detector and why is this behavior observed? The intensity of light from the light source is 300.0 photons/sec. (Only 10% of the photons are actually shown on the screen.)
If T = 30%, then 30% of the photons passing through the sample reach the detector and the other 70% are absorbed by the analyte. Run each simulation sufficiently long to detect at least 1000 photons. (Not all photons are shown on the screen.) Because the intensity for the blank is used to calculate all absorbances, it is especially important that the intensity for the blank be known accurately.
The analyte is the substance that absorbs the light. (Literally, it is the substance that is being analyzed in the experiment.) The concentration is represented by the symbol c and is typically measured in mole L -1 . Each simulation will be performed using a different concentration to isolate the effect of the concentration on the absorption of light. The intensity of light from the light source is 500.0 photons/sec. (Only 10% of the photons are actually shown on the screen.)
The number and positions of the peaks in the spectrum is determined by the electronic structure of the compound, which in this case depends upon the identity of the metal and the identities, number, and geometry of the surrounding ions. An alternative way to express this concept is to recognize that the spectrum of light reaching the eye is the product of the spectrum of the incident light (white light) and the transmittance spectrum.
A set of negative charges (white spheres) are positioned around the metal center using one of four geometries: linear, square planar, tetrahedral, and octahedral. (Obviously other geometries are possible, but these four geometries are the most common.) The diagram at the right shows the absolute energy of the individual orbitals (E) or the energy difference from the average (spherical field) energy (ΔE).
The splitting is significantly smaller for a tetrahedral geometry than for an octahedral geometry: Δ t = 4/9 Δ o . (Why is Δ t so much smaller than Δ o ? If necessary, revisit the Crystal Field Theory exercise and carefully compare the nature of the overlap of point charges and orbitals for the tetrahedral and octahedral cases.)