Assessment Exam:Instrumental and Analytical Chemistry

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  1. An appropriate method for determining the identity of a thin plastic film is
    A. Fourier-transform infrared spectroscopy
    B. nuclear magnetic resonance.
    C. atomic absorption.
    D. gas chromatography.
    E. polarography.

  2. The refractive index detector used in liquid chromatography is an example of
    A. a laser based detector.
    B. an integrating detector.
    C. a destructive detector.
    D. a selective detector.
    E. a bulk property detector.

  3. In gas chromatography, the main advantage of the flame ionization detector (FID) over the thermal
    conductivity detector is that the FID is

    A. more sensitive to organic compounds.
    B. responsive to H2O and CO2.
    C. better suited to temperature programming.
    D. a concentration sensitive detector.
    E. more sensitive to compounds containing electronegative functional groups.

  4. Which statements best describe the advantages of capillary gas chromatography columns over megabore and packed columns?
    I Capillary columns handle larger samples.
    II Capillary columns have higher efficiencies.
    III Capillary columns have higher resolutions.

    A. I only
    B. II only
    C. I and III only
    D. II and III only
    E. I, II, and III

  5. Gradient elution methods are used in high-performance liquid chromatography to
    A. maintain the stability of the bonded stationary phase.
    B. flush impurities out of the front of the column at the end of a run.
    C. modulate the refractive index of the solvent found in the detector.
    D. vary the partition ratios for the sample components of varying polarities.
    E. linearize the calibration plot.


  6. In size exclusion chromatography, retention of sample molecules is based on
    A. ion exchange equilibria between the mobile and the stationary phase.
    B. infiltration of sample molecules into cavities in the stationary phase.
    C. differences in electrophoretic mobility of sample molecules.
    D. ion polarity differences between sample molecules.
    E. changes in induced dipole moment.

  7. Excitation of molecules with radiation in different regions of the electromagnetic spectrum causes
    different changes to the molecule. Indicate which pair is not true.

    radiation : change to molecule
    A. radio frequency : electron excitation
    B. microwave : rotational excitation
    C. visible : valence electron excitation
    D. infrared : vibrational excitation
    E. ultraviolet : valence electron excitation


  8. When utilizing a Mattauch-Herzog double-focusing mass spectrometer with a spark source, what is
    the resolving power required to separate iron (56Fe+, m/z = 55.93494) from silicon (28Si2+, m/z = 55.95386)

    A. 1/0.01892
    B. (55.93494+55.95386)/[2x(55.93494-55.95386)]
    C. (55.93494+55.95386)2/[2x(55.93494-55.95386)]
    D. (55.93494-55.95386)
    E. Not enough information is provided to do the calculation for this instrument.

  9. An important advantage of a double-beam spectrophotometer over a single-beam spectrophotometer is that it permits
    A. cancellation of drift.
    B. narrower slit widths to be used.
    C. maximum slit widths to be used.
    D. rapid response systems to be used.
    E. cancellation of source-induced fluorescence.

  10. Palladium reacts with Thio-Michler's ketone to form a colored complex (1 Pd:4 ketone) that
    absorbs at 520 nm. A 0.20 ppm (mg/mL) solution of palladium, to which
    the ketone has been added gave an absorbance of 0.390 at 520 nm in a 1.00 cm cell. Calculate the
    molar absorptivity, e, of the Pd: Thio-Michler's ketone at 520 nm. [molar
    mass of Pd = 106.4 gmol-1]

    A. 0.0195 Lmol-1cm-1
    B. 21,000 Lmol-1cm-1
    C. 1,950 Lmol-1cm-1
    D. 0.0036 Lmol-1cm-1
    E. 210,000 Lmol-1cm-1

  11. A chemical system obeys Beer's Law. If a 1.25 x 10-4 M sample of a compound
    gives a 10.0% transmittance in a 1.00 cm cell, what is the concentration of a sample that reads 20.0 %
    transmittance in a 2.00 cm cell?

    A. 8.0 x 10-6 M
    B. 3.1 x 10-5 M
    C. 4.4 x 10-5 M
    D. 6.33 x 10-5 M
    E. 2.5 x 10-5 M

  12. Which statement is true regarding fluorescence and phosphorescence processes?
    A. Phosphorescence requires excitation with visible light while fluorescence requires UV.
    B. Phosphorescence occurs at longer wavelength than that of the excitation source but fluorescence occurs at shorter wavelength.
    C. Phosphorescence involves intersystem crossing following the excitation while fluorescence does not.
    D. Phosphorescence typically occurs on a much shorter lifetime than fluorescence.
    E. Phosphorescence is much more common than fluorescence.

  13. Which statement best explains the fact that atomic absorption spectrophotometry is often more
    sensitive than flame emission spectrometry?

    A. Hollow cathode discharge tubes, often used as sources in atomic absorption, have much greater radiant power output than do ordinary flames.
    B. At the temperature of the typical flame, the population of the ground state atoms is much greater than the population of the excited state atoms.
    C. An absorption line in a flame is always much broader than an emission line because of the Doppler effect.
    D. The detectors employed in studying the absorption of radiation are inherently more sensitive than those used to measure the emission of radiation.
    E. Materials of construction permit higher flame temperatures in instruments designed for absorption studies.

  14. NMR spectrometers use a magnet with as large as field strength as possible to
    A. improve field homogeneity.
    B. increase the coupling constant relative to the frequency separation of the chemical shifts.
    C. increase the frequency separation of the chemical shifts relative to the coupling constant.
    D. increase the spatial capacity factor.
    E. increase the quantum efficiency.

  15. Based on the two point calibration given below, determine the concentration of lead in an unknown
    sample based on the absorbance of that sample.

    sample 1 absorbance = 0.074 for a 5.00 ppm lead standard
    sample 2 absorbance = 0.255 for a 20.0 ppm lead standard
    unknown absorbance = 0.120

    A. 5.25 ppm
    B. 8.81 ppm
    C. 10.8 ppm
    D. 14.9 ppm


  16. A forensic toxicologist has a sample of a white substance that has been identified as cocaine. She
    needs to determine the concentration of the cocaine because the police think they arrested a major
    distributor with nearly pure cocaine. Before she extracts the cocaine, she adds some lidocaine as an
    internal standard, both to the suspect cocaine and to samples of known purity. She weighs the same
    masses of each sample, extracts each with the same process, and then injects them into a GC. She will
    use the ratio of the area of the cocaine peak to the area of the lidocaine peak for her calibration plot.
    The internal standard approach will correct for all but one of the following problems. Which problem
    will not be corrected?

    A. injecting 1.1 or 1.2 mL, rather than 1.0 mL.
    B. having extraction efficiencies that are uniformly less than 100%, perhaps as low as 60%.
    C. hitting the "start" button late, two or three seconds after injection.
    D. having a compound that coelutes with the lidocaine in the unknown sample.
    E. having a contaminant that causes a baseline shift in the unknown sample.

  17. You receive a 20-mL sample of old motor oil. There is some concern about which metal parts of
    the engine are subject to abnormal wear. Traces of worn metal will be present in the oil. How would
    you analyze the oil both qualitatively and quantitatively for the principal metal constituents?

    A. run directly with magnetic resonance spectroscopy
    B. inject and determine by gas chromatography
    C. dilute in organic solvent and use ultraviolet spectrophotometry
    D. digest and use ICP emission spectroscopy
    E. use atomic force microscopy on the individual metal particles

  18. Which is not a method for detecting determinate (systematic) errors?
    A. analysis of standard samples
    B. calculation of the standard deviation
    C. variation of the sample size used in the analysis
    D. analysis of the sample by another method

  19. In potentiometric measurements using ion-selective electrodes, the
    A. measured potential is a linear function of the analyte concentration.
    B. ionic strength must be the same for the standards and the unknown.
    C. concentration of the analyte must be held constant.
    D. current is directly proportional to the analyte concentration.

  20. Why is it easier to analyze a mixture of atomic species by absorption spectroscopy than it is to
    analyze a mixture of molecular species?

    A. Atomic species do not have side reactions.
    B. Molecular species do not absorb light.
    C. Molecules are larger, therefore more difficult to analyze.
    D. Atomic spectra have narrower lines that are easier to resolve than the features of molecular spectra.

  21. Two weak acids, HA (pKa = 3.0) and HB (pKa = 5.0) have equal
    partition coefficients for extraction from water to n-octanol. An aqueous solution with equal
    concentrations of HA and HB is extracted with n-octanol. For equal volumes of water and n-octanol, which pH will provide the best separation of HA and HB?

    A. 2.0
    B. 3.0
    C. 4.0
    D. 5.0

  22. Which compound is expected to have the greatest retention time in a reversed-phase HPLC
    column?
    A. sodium acetate, CH3COONa
    B. phenol, C6H5OH
    C. butanoic acid, CH3CH2CH2COOH
    D. n-dodecane, CH3(CH2)10CH3