# Quant. Anal. Chp 18 Spectromet

Flashcard maker : Patricia Smith
 [Dual Nature of Light]Wave:
 -Explains physical properties of light itself.-Physicist
 [Dual Nature of Light]Particle (Photon):
 -Explains how light interacts with matter.-Biologist/Chemist
 1. Relation between frequency and wavelength:   2. Speed of light in other medium?
 1. c= νλ    2. c/n
 Relation between energy and frequency (or wavelength):
 E=h ν = h(c/ λ) Smaller Wavelength →Higher Frequency → More Energy
 What are the ways light interacts with matter?
 Light can be: Reflected Refracted Scattered Emitted Absorbed
 Absorption-
 Transfer of energy from photon to atom or molecule which produces transition from a lower energy to a higher energy level.
 Emission-
 Production of photon of energy from atom or molecule which is originally in a higher energy level and which returns atom or molecule to a lower energy level.
 What are the 5 main components of a spectrophotometric experiment?
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 Transmittance:
 The fraction of incident light that passes through a sample. T = P/P0 P0 is the irradiance (radiant power) striking the sample and P is irradiance emerging from other side of sample. P ≤ P0 As %: %T = (P/P0) * 100%
 Absorbance:
 Most useful quantity for chemical analysis. A = log(P0/P) = -log(T)
 Beer-Lambert Law:
 Aλ=ελbc   The reason why absorbance is so important is that absorbance is proportional to the concentration of light-absorbing molecules in the sample.
 Limitations of Beer-Lambert Law:
 Works well for dilute solutions (≤ 0.01 M) of most absorbing substances. Light must be monochromatic Pathlength must be constant (square cuvette) (typically is 1 cm) Sample should not: Fluoresce or phosphoresce Scatter light (heterogeneous) Change its chemical composition
 Common Cuvets for Ultraviolet and Visible Measurements:
 Standard 1-cm path Cylindrical Microcells