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Ultraviolet–visible spectroscopy Knowledge-Based Practice

Chemistry · Applied Chemistry · Chemistry · Analytical Techniques

5 Chemistry practice questions on Ultraviolet–visible spectroscopy. Questions that assess core concepts and understanding.

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Questions

  1. 1.

    In quantitative ultraviolet–visible (UV-Vis) spectrophotometry, which phenomenon represents a chemical deviation from the Beer–Lambert law?

    • A) The leakage of stray radiation into the detector system at wavelengths outside the nominal bandpass
    • B) The concentration-dependent dimerization, dissociation, or solvolysis of the absorbing analyte
    • C) The transmission of polychromatic light consisting of wavelengths with unequal molar absorptivities
    • D) The optical mismatch and refractive index discrepancies between the sample and reference cells
  2. 2.

    In ultraviolet–visible (UV-Vis) spectroscopy, which electronic transition in an organic carbonyl compound requires the lowest excitation energy and consequently absorbs at the longest wavelength?

    • A) σ→σ∗\sigma \to \sigma^*
    • B) n→σ∗n \to \sigma^*
    • C) π→π∗\pi \to \pi^*
    • D) n→π∗n \to \pi^*
  3. 3.

    In ultraviolet–visible (UV-Vis) spectroscopy, which term describes the shift of an absorption band toward a longer wavelength?

    • A) Bathochromic shift (red shift)
    • B) Hypsochromic shift (blue shift)
    • C) Hyperchromic effect
    • D) Hypochromic effect
  4. 4.

    In a standard ultraviolet–visible (UV-Vis) spectrophotometer, which radiation source is conventionally used to provide continuous emission across the ultraviolet region (190–380 nm)?

    • A) Deuterium arc lamp
    • B) Tungsten-halogen lamp
    • C) Hollow cathode lamp
    • D) Silicon carbide Globar source
  5. 5.

    In ultraviolet–visible (UV-Vis) spectrophotometry, which cuvette material must be used when measuring absorbance at wavelengths below 320 nm, and why?

    • A) Borosilicate glass, because it absorbs stray infrared radiation and prevents thermal broadening.
    • B) Polystyrene plastic, because it exhibits negligible background absorbance across the far-ultraviolet region.
    • C) Fused quartz, because it is transparent to ultraviolet radiation and does not absorb light above 190 nm.
    • D) Standard optical crown glass, because its refractive index closely matches that of aqueous solvent systems.

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