Spectrophotometry I.Electromagnetic Radiation = Light A.What is Light? 1.Visible light is a...

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Transcript of Spectrophotometry I.Electromagnetic Radiation = Light A.What is Light? 1.Visible light is a...

  • SpectrophotometryElectromagnetic Radiation = LightWhat is Light?Visible light is a particular kind of electromagnetic radiationX-rays, UV, Infrared, Microwaves, and Radio waves are all light formsLight is a form of EnergyAll light travels in waves at the speed of light = c = 3 x 108 m/s

  • Characteristics of LightWavelength = distance between two peaks in a wave l (lambda) is the symbolMeters = m is the unitFrequency = number of complete waves passing a given point per second n (nu) is the symbolHertz = Hz = s-1 is the unitAmplitude = A = measure of the intensity of the wave, brightnessThe speed of light is constant: c = x l and n are inversely proportionalIf one increases, the other decreasesTheir product is always the speed of light = c = x = 3 x 108 m/s

  • II. Spectroscopy = using light to investigate a compoundHow the experiment works

    What color do we see?a) What we see as the color of a compound is the complementary color to what the compound absorbsb) Example: Absorbs red, we see green

  • Beers LawAbsorbance tells us how much light is absorbed by the molecule

    B.A = elc (y = mx + b) describes the absorption of light in a solutionl = the length of the cell containing the solution, usual 1 cmc = concentration in mol/L = M e = Molar extinction coefficient = constant for a given molecule at a given wavelength of light = how well the molecule absorbs lightPercent T0 10 25 50 75 100 2.0 1.0 0.6 0.3 0.1 0AbsorbanceAbsorbanceConcentration (mol/L)1.0


    0.00 0.00001 0.00002 0.00003 0.00004 0.00005Slope = el [L/molcm][cm]e 18,000 for our red dye

  • Todays ExperimentMake a Beers Law Calibration Curve using a Stock Solution

    Calculating the concentration of your stock solution: (Ex: 0.0788g/L)

    Calculations for the calibration curve samples: M1V1 = M2V2

    An Excel Template is available at faculty.swosu.edu/tim.hubin in the Shared Folder link called Spectrophotometry Lab Excel sheet

    Sample #123456mL DyeStock Soln0.501.001.502.002.503.00mL Water9.509.008.508.007.507.00Molarity

  • Find the concentration of an unknown sample of the red dyeWe will give you an unknown amount of the stock solutionDilute it to 25 ml in a volumetric flaskCalculate the absorbance (from %T) on the Spec. 20Use your spreadsheet to calculate the concentration from the absorbanceExample Calculation: %T = 15% for your diluted unknown

    Make 100ml of a solution of a known concentration (2.5 x 10-5 M)

  • Chromic Acid Splash in Eyes

    Frayed Electrical Cord Fire