1 / 0

Introduction to Spectrophotometry & Beer’s Law

Introduction to Spectrophotometry & Beer’s Law. AP Chemistry Mrs. Weston. What is spectrophotometry?.

soren
Télécharger la présentation

Introduction to Spectrophotometry & Beer’s Law

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Introduction to Spectrophotometry & Beer’s Law

    AP Chemistry Mrs. Weston
  2. What is spectrophotometry? A type of spectroscopy that studies the transmission or reflection of different frequencies of the electromagnetic spectrum (specifically visible, near-IR and near-UV ranges) by a sample of matter (usually a soln)
  3. Other types of spectroscopy Atomic absorption spectroscopy Atomic emission spectroscopy Mass spectroscopy Nuclear magnetic resonance (NMR) Fourier transform infrared (FTIR) spectroscopy
  4. Spectrophotometer Measures absorbance or transmittance of light as a function of wavelength Sample is placed into cuvette Light of selected wavelength is passed through sample Amount of light absorbed is measured
  5. Because other compounds in a solution (or the solvent itself) may absorb the same wavelengths as the compound being analyzed, the absorbance of the sample is compared to a reference blank. Ideally, the reference blank should contain everything found in the sample solution except the substance being analyzed. When using a Spec 20, every time the wavelength is changed, the instrument needs to be re-zeroed.
  6. How it works Transmission = I/Io Absorbance = log T
  7. How to choose wavelength We want to analyze samples using the wavelength at which the most light is absorbed – Wavelength of maximum absorption (λmax)
  8. Beer’s Law Amount of light absorbed is proportional to the concentration of the solution A = abc A = absorbance a = proportionality constant (ε = molar absorptivity) b = path length (same for entire experiment) c = concentration (M)
  9. What does this tell us? There is a direct relationship between absorbance and concentration. When we prepare solutions of known concentration and analyze them at λmax, we can plot absorbance as a function of concentration.
  10. The concentration of the unknown can be determined by finding its absorbance and plugging it into the equation for the best fit line. y = mx + b
  11. Uses of spectrophotometry Determining concentration of any colored solution (Fe, Cu, Co, Ni, MnO4, etc) Biology Biochemistry Forensic science
More Related