221-chapter-18

# 221-chapter-18 - Fundamentals of Spectrophotometry...

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Fundamentals of Spectrophotometry Introduction 1.) Colorimetry An analytical technique in which the concentration of an analyte is measured by its ability to produce or change the color of a solution - Changes the solution’s ability to absorb light 2.) Spectrophotometry Any technique that uses light to measure chemical concentrations A colorimetric method where an instrument is used to determine the amount of analyte in a sample by the sample’s ability or inability to absorb light at a certain wavelength. Colorimetry Instrumental Methods (spectrophotometry) Non-Instrumental Methods

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Fundamentals of Spectrophotometry Introduction 3.) Illustration Measurement of Ozone (O 3 ) Above South Pole - O 3 provides protection from ultraviolet radiation - Seasonal depletion due to chlorofluorocarbons Spectra analysis Chain Reaction Depletion of O O cycle
Fundamentals of Spectrophotometry Properties of Light 1.) Particles and Waves Light waves consist of perpendicular, oscillating electric and magnetic fields Parameters used to describe light - amplitude (A) : height of wave’s electric vector - Wavelength ( λ ) : distance (nm, cm, m) from peak to peak - Frequency ( ν ): number of complete oscillations that the waves makes each second Hertz (Hz): unit of frequency, second -1 (s -1 ) 1 megahertz (MHz) = 10 6 s -1 = 10 6 Hz

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Fundamentals of Spectrophotometry Properties of Light 1.) Particles and Waves Parameters used to describe light - Energy (E ): the energy of one particle of light (photon) is proportional to its frequency ν h E = where: E = photon energy (Joules) ν = frequency (sec -1 ) h = Planck’s constant (6.626x10 -34 J-s) As frequency ( ) increases, energy (E) of light increases
Fundamentals of Spectrophotometry Properties of Light 1.) Particles and Waves Relationship between Frequency and Wavelength Relationship between Energy and Wavelength λ ν λν / c c = = where: c = speed of light (3.0x10 8 m/s in vacuum)) ν = frequency (sec -1 ) λ = wavelength (m) ~ hc hc E = = where: = (1/ λ ) = wavenumber ~ As frequency ( ) decreases, energy (E) of light increases

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Fundamentals of Spectrophotometry Properties of Light 2.) Types of Light – The Electromagnetic Spectrum Note again, energy (E) of light increase as frequency ( ν ) increases or wavelength ( λ ) decreases
Fundamentals of Spectrophotometry Properties of Light 2.) Types of Light – The Electromagnetic Spectrum

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Fundamentals of Spectrophotometry Absorption of Light 1.) Colors of Visible Light Many Types of Chemicals Absorb Various Forms of Light The Color of Light Absorbed and Observed passing through the Compound are Complimentary
Fundamentals of Spectrophotometry Absorption of Light 2.) Ground and Excited State When a chemical absorbs light, it goes from a low energy state ( ground state ) to a higher energy state ( excited state ) Only photons with energies exactly equal to the energy difference between the two electron states will be absorbed

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## This note was uploaded on 05/09/2010 for the course CHEM 221 taught by Professor Dr.robertpowers during the Fall '07 term at San Diego.

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221-chapter-18 - Fundamentals of Spectrophotometry...

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