Exam III Flashcards
Cu->cu2+ and 2e-
Oxidation
2(AG+ + e-)-> 2 AG
Reduction
Reduction
Gain of electrons
Oxidation
Loss of electrons
Cathode
Where reduction happens
Anode
Where oxidation occurs
dG=-nFE
N-number of transferred
F-96500 c/mol
E- potential
Standard reduction potential
Ecell=Eright-Eleft
Potentiometry
measure potential and relate to concentration by nernst equation
Potentiometry
measure potential and relate to concentration by nernst equation
ref electrode II soln I indicator electrode
Reference electrodes
Calomel-Hg I Hg2Cl2, KCl II
E=0.2444
Silver silver chloride electrode- Ag I AgCl, KCl II
E=0.199
Membrane electrodes
glass electrodes
liquid membrane electrodes
crystalline membrane electrodes
gas sensing probes
glass electrodes
ref electrode II external analyte soln I glass membrane I internal ref soln of known [], Cl-, AgCl I Ag
charge difference creates potential across membrane
H+, Li+, Na+, Nh4+
liquid membrane electrode
like glass but polymeric ion exchange; Ca2+, Cl-, NO3-, ClO4-, K+
crystalline membrane electrode
solid crystalline materials; Br-, Cd2+, Cl-, Cu2+, CN-, F-, I-, Pb2+, Ag+, S2-, SCN-
gas sensing probes
detect change in pH due to dissolved gas; CO2, NO2, H2S, SO2, HF, HCN, NH3
Coulometry
measure charge necessary to completely to completely reduce sample
Voltametry
control potential, measure current
3 electrode cell- working and counter in electrolysis circuit and working and reference in reference circuit
working/counter electrodes
Pt, Au, glassy carbon, pyrolytic graphite
Dropping mercury electrode (DME)
problems with electrode detecting analyte
diffusion-analyte must break barrier
migration due to electric field, and convection
linear scan voltammetry application
dissolved O2 sensors
glucose sensors
Differential Pulse Polarography (DPP)
+: resolution (.04-.05 mV)
mixtures
-: sensitivity (10E-7-10E-8 M DL)
Stripping methods
can be used to determine mix of metals
analyte must be able to deposit out as solid
DL=10E-6-10E-9
DPP and stripping methods
must have relatively clean sample
eliminate diffusion problems
Atomic Spectroscopy
quantifies atomic species-ions or atoms, not molecules
line spectra
absorbance, emission, fluorescence
Atomic Spectroscopy Instrumentation
Source, atomixer, monochromator, detector, read out
Atomic Spec source
hollow cathode tubes specific for a metal
Atomic Spec monochromator
grating
Atomic Spec Detector
PMTs-detect 1 element at a time
DAD/CCD- allow multiple elements at a time
Atomic Spec Atomizers
Flame
electrothermal/graphite furnace
flame atomizer
aspirates soln into flame, evaporating
absorbance, emission
cheap and easy
least sensitive (ppm)
electrothermal/graphite furnace
heat tube to volatilize sample
absorbance, fluorescence
medium cost, medium ease of use
medium sensitivity (10-100ppm)
Inductively coupled plasma (ICP)
emission MS multielement analysis most expensive, hardest to use high sensitivity (ppb-ppt)
Flame instrument
source, chopper, reference and sample cells, monochromator, detector, read out
Ion chromatography
uses HPLC instrumentation (solvent res., pump, sample injector, column, detector, readout)
column- stationary phase is charged
detector-conductivity detector
DL in ppm
+: ion analyses, multielement, low cost
-: not very low DL, requires analyte in soln
X-ray Fluorescence
absorb xray proton, ionize e- out of atom, creates hole in core e-
wavelength and energy dispersive
no soln required
problems with matrix effects
DL: .01-100%mass
+: nondestructive, no sample prep, portable
-: difficulty in calibration, relatively high DL
Laser induced breakdown spectroscopy
laser to sample creates plasma, heat excites metals, emits light which is transferred fiber optically to monochromator, and PMT detector
+: no sample prep, nondestructive, spatial resolution 1-100um, portable
-: matrix effects cause hard to calibrate, precision 5-10%, DL: 1-100ppm
