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Electrochemistry
Electrochemical Methods
Spectroscopy
Spectroscopy Methods
Chromatography
100
What process occurs at the cathode of an electrochemical cell?
Reduction
100
What is the common reference electrode in a pH meter?
Ag/AgCl
100
What is the wavelength range for visible light? (Must give correct units!)
380-780 nm (accept 350 - 750nm)
100
What are the two theories that describe electromagnetic radiation?
Wave and photon theories
100
In GC, what is the effect of increasing the column temperature on retention time?
decreases retention time
200
Calculate the Ecell for the following: Cu|Cu2+ (1 M)|| Ag+ (1M) |Ag E0 Cu2+|Cu = 0.337V E0 Ag+|Ag = 0.799V
Ecell = Ecathode - Eanode = 0.462 V
200
Which of these electrochemical methods include current in their measurements? Potentiometry Electrogravimetry Coulometry Voltammetry
All except potentiometry
200
What is Beer's law?
A = ebc
200
In molecular absorption spectroscopy, why are the spectra bands rather than lines?
The addition of rotational and vibrational energies
200
What are the two terms that define column efficiency?
N (number of plates) H (plate height)
300
What is the Nernst equation for the reaction below? Ag+ + e -> Ag(s)
E = E0 - 0.0592/1 log (1/[Ag+])
300
What develops across the boundary between two electrolyte solutions that have different compositions?
A liquid-junction potential (Ej
300
Which is the more sensitive: Phototubes or Photomultiplier tubes? Why?
Photomulitplier tubes because it has a series of dynodes that amplify the electrons from the initial radiation to provide a higher sensitivity.
300
What spectroscopic method uses a line source as the excitation source?
Atomic Absorption Spectroscopy
300
When you create a calibration curve using internal standards in GC, what are the axes?
X = concentration; Y = peak area of analyte/peak area of I.S.
400
What assumption do we make when using the Nernst equation with concentrations?
The activity is proportional to concentration (there is sufficient ionic strength)
400
In voltammetry, what is E1/2 and what is the significance of this value?
It is the potential what corresponds to half the limiting current and good approximation of standard potential.
400
What term describes the difference between excitation and emission spectra in Fluorescence?
Stokes shift
400
Which type of species would you expect to absorb in the UV range? Benzene or Copper(II) solution
Benzene
400
What is N for a peak with retention time of 6.00 min and peak width of 2.00 min?
N = 144
500
An ion-selective electrode is used to determine the chloride concentration in a water sample. What would the axes be for a calibration plot for the chloride electrode?
X- pCl Y- potential (mV)
500
Copper is deposited from a solution of Cu(II). Oxygen is evolved at the anode. The cell has a resistance of 3.60 Ohms and has a current of 0.10 A. The theoretical potential (Ecell) = -0.600 V Calculate the Eapplied where the overpotential of oxygen is 0.50 V.
Eapplied = Ecell - IR - Overpotential Eapplied = -0.600 V - (0.1 A x 3.60 Ohms) - 0.50 V = -1.46 V
500
What are two limits to the Beer's law?
Must be dilute solutions Chemical equilibrium must be taken into account if chemical deviations Polychromatic radiation Stray light
500
What makes FTIR different than typical molecular absorption spectroscopy techniques? Name two things.
Different source (for IR range - Nernst glower) No monochromator needed because sample all frequencies at 1x (using interferometer) Detectors are heat detectors
500
What is the difference between isocratic and gradient elution in LC? Why use the gradient elution?
Isocratic - solvent composition remains constant Gradient - composition of solvent is changed continuously Use gradient when wide range of polarities in sample and it can improve the efficiency of elution