Chemistry 2272F Study Guide - Final Guide: Stray Light, Photomultiplier, Rayleigh Scattering

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31 Jan 2013

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Analytical Chemistry Final
Electrochemistry Study of chemical energy and electrical energy based on reduction &
oxidation reactions.
Electro-analytical Chemistry Use of electrical measurements on a chemical system for
analytical purposes…
Redox Reaction (Titration) Transfer of electrons from one species to the other
Oxidation The increase in oxidation number/loss of electrons
Oxidizing Agent Substance causing the oxidation reaction
Reduction The decrease in oxidation number/gain of electrons
Reducing Agent Substance causing the reduction
Voltaic Cell Generates a spontaneous voltage by a chemical redox reaction e.g. battery
Cathode Electrode where the reduction takes place
Anode Electrode where the oxidation takes place
Line Notation
Anode is on the left, Cathode is on the right
“|” Indicates phase boundary
“||” Indicates the salt bridge
Ignore Spectator ions
**If half-cell has no solid species to serve as electrode, use an inert electrode such at Pt or
**Concentrations should be entered if applicable.**
Standard Potentials Standard reduction potentials (1 M and 1 atm) are outlined in table
Cell Potential Comparison between the anode and cathode reduction potentials
    
**Standard Reduction Potentials used for both, negative sign is valid**
Nernst Equation To determine cell potential at non-standard conditions
  
  
   
 
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Redox Titration Curve
Initially Only one species is present (ie. Fe2+). Therefore no potential may be
Before Equivalence Analyte in excess, however some product is formed. Analyte
therefore controls potential
Equivalence Point Tricky to calculate (use equation)
After Equivalence Titrant determines potential.
Equivalence Point Equation:
 
 
Factors affecting the sharpness of the curve:
1. Concentration
2. Completeness/Spontaneity
3. Strength of Reducing Agent/Oxidizing Agent
** Endpoint detection can occur are either potential measurements or visual indication **
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Introduction to Spectrometric Methods
** Absorbance is evident by the intensity of color, which is proportional to the concentration **
Energy States of Matter
- Energy is quantized in discrete energy levels; which is a property of the molecule/atom
Excited State Any energy state that is higher than the lowest energy state
Ground State The lowest level energy state of an atom/molecule
Emission Light given off during relaxation
Electromagnetic radiation emitted as an excited particle relaxes
Absorption Electromagnetic energy is transferred from a photon to a molecule/atom
Causes transition from ground state to excited state
Only occurs if the energy level exactly matches the delta E
Quantitative Aspects of Spectrochemical Measurements
Emission Signal is proportional to the concentration of analyte
At some point this falls off due to interactions
  
Absorption Beer-Lambert‟s Law outlines the relationship
Absorption of a wavelength is linearly related to concentration
  
Chemical Analysis:
1. Choose wavelength by conducting a scan (λmax should be chosen)
a. This is because aλ is most constant for slit width
2. Run calibration Standards (construction of linear model)
3. Run unknown sample
4. Determine unknown conc. from calibration curve
Instruments for Optical Spectroscopy
Absorbance Spectrometer Measures absorbance of monochromatic light across a
sample. A narrow band of light is isolated
Fluorescence Spectrometer Measures light emitted by the analyte that has been excited
by absorption of light.
Emission Spectrometer Measures light emitted by a sample excited thermally or
Sources of Radiation
Continuum Sources Broad spectrum of light
Requires a wavelength selector to be useful
Example: Blackbody source of light (temperature dependent)
Line Source Few discrete (monochromatic) wavelengths
Based on emission of atoms (nothing to do with temperature)
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