Spectrophotometry Knowledge-Based Download PDF

Questions

1. 1.

   In an absorption spectrophotometer, which component is primarily responsible for dispersing polychromatic radiation into its constituent wavelengths and isolating a narrow spectral band?

   • A) Photomultiplier tube
   • B) Deuterium arc lamp
   • C) Monochromator
   • D) Optical beam splitter
2. 2.

   In quantitative absorption spectrophotometry, why are analytical measurements routinely performed at the wavelength of maximum absorbance ($\lambda_{\max}$)?

   • A) To prevent electronic excitation from inducing photochemical degradation of the analyte
   • B) To eliminate background absorption caused by non-absorbing solvent molecules
   • C) To achieve maximum analytical sensitivity and minimize errors arising from slight wavelength setting inaccuracies
   • D) To guarantee that percent transmittance varies linearly with analyte concentration
3. 3.

   In absorption spectrophotometry, what is the primary purpose of measuring a blank solution to zero the instrument prior to sample analysis?

   • A) To eliminate internal stray light generated by the monochromator and optical components.
   • B) To compensate for light attenuation caused by the solvent, reagents, and cuvette reflections.
   • C) To calibrate the wavelength scale of the monochromator across the measurement range.
   • D) To increase the intrinsic molar absorptivity of the analyte to enhance measurement sensitivity.
4. 4.

   Why are fused silica (quartz) cuvettes required rather than optical glass cuvettes when performing spectrophotometric measurements in the ultraviolet (UV) region?

   • A) Optical glass undergoes photochemical degradation and reacts irreversibly with typical solvents under UV irradiation.
   • B) Quartz cuvettes selectively refract stray radiation to maintain beam collimation at short wavelengths.
   • C) Optical glass induces severe light scattering due to microscopic surface irregularities at high photon energies.
   • D) Optical glass strongly absorbs radiation at wavelengths below approximately 350 nm, rendering it opaque in the UV range.
5. 5.

   Which of the following phenomena represents a chemical cause of deviation from the Beer-Lambert law in UV-Vis spectrophotometry?

   • A) Stray radiation striking the detector without passing through the sample absorption cell
   • B) Polychromatic light transmission resulting from a wide exit slit on the monochromator
   • C) Electrostatic interactions between neighboring ions in solutions exceeding 0.01 M
   • D) Reversible dissociation or association of the absorbing analyte in an unbuffered solution