MCQ Quiz- Polarography

MCQ Quiz: Polarography

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Polarography is a specialized electroanalytical technique used to analyze reducible or oxidizable substances. For B.Pharm students, understanding its principles, particularly the significance of the dropping mercury electrode (DME) and the Ilkovic equation, is key to appreciating trace metal analysis and the quantification of certain organic compounds. This quiz delves into the fundamentals of polarography, a sensitive method for determining the concentration and identity of electroactive species in a solution.

  1. Polarography is a type of voltammetry that utilizes which specific working electrode?
    • Platinum electrode
    • Glass electrode
    • Dropping Mercury Electrode (DME)
    • Calomel electrode
    Answer: Dropping Mercury Electrode (DME)
  2. The fundamental principle of polarography involves measuring the current as a function of the:
    • Applied potential
    • Resistance
    • Temperature
    • pH
    Answer: Applied potential
  3. The Ilkovic equation in polarography relates the diffusion current to the:
    • Half-wave potential
    • Concentration of the analyte
    • Viscosity of the solution
    • Temperature
    Answer: Concentration of the analyte
  4. The characteristic S-shaped curve obtained in polarography is known as a:
    • Titration curve
    • Polarogram
    • Chromatogram
    • Spectrum
    Answer: Polarogram
  5. In a polarogram, the limiting current that is proportional to the analyte’s concentration is the:
    • Residual current
    • Migration current
    • Diffusion current
    • Catalytic current
    Answer: Diffusion current
  6. The half-wave potential (E½) in a polarogram is used for:
    • Quantitative analysis
    • Qualitative analysis
    • Determining the purity of mercury
    • Measuring the drop time
    Answer: Qualitative analysis
  7. What is the primary advantage of the Dropping Mercury Electrode (DME)?
    • It has a large surface area.
    • It provides a continuously renewed, smooth, and reproducible electrode surface.
    • It is not toxic.
    • It can be used at very high positive potentials.
    Answer: It provides a continuously renewed, smooth, and reproducible electrode surface.
  8. The purpose of adding a supporting electrolyte (like KCl) in a large excess is to:
    • Increase the diffusion current
    • Eliminate the migration current
    • Act as a catalyst
    • Buffer the solution
    Answer: Eliminate the migration current
  9. The small current that flows in a polarographic cell even in the absence of the analyte is called the:
    • Diffusion current
    • Limiting current
    • Residual current
    • Faradaic current
    Answer: Residual current
  10. The Rotating Platinum Electrode (RPE) is an alternative to the DME and is a type of:
    • Reference electrode
    • Micro-electrode
    • Counter electrode
    • Ion-selective electrode
    Answer: Micro-electrode
  11. According to the Ilkovic equation, the diffusion current is directly proportional to the:
    • Square root of the concentration
    • Square of the concentration
    • Concentration of the analyte
    • Logarithm of the concentration
    Answer: Concentration of the analyte
  12. The half-wave potential (E½) is the potential at which the current is equal to:
    • The residual current
    • The maximum diffusion current
    • Half the diffusion current
    • Zero
    Answer: Half the diffusion current
  13. A major disadvantage of the Dropping Mercury Electrode is:
    • The toxicity of mercury
    • Its easily oxidizable nature, limiting its use at positive potentials
    • The inconvenience of mercury drops
    • All of the above
    Answer: All of the above
  14. In polarography, the solution being analyzed is generally:
    • Stirred continuously
    • Kept unstirred or quiescent
    • Heated
    • Cooled to freezing
    Answer: Kept unstirred or quiescent
  15. To remove dissolved oxygen from the analyte solution, the solution is purged with:
    • Oxygen gas
    • Air
    • An inert gas like nitrogen
    • Chlorine gas
    Answer: An inert gas like nitrogen
  16. The diffusion current in polarography results from the movement of ions to the electrode due to a:
    • Potential gradient
    • Concentration gradient
    • Temperature gradient
    • Pressure gradient
    Answer: Concentration gradient
  17. Which component is NOT part of a basic polarographic cell?
    • Working electrode (DME)
    • Reference electrode
    • Counter (auxiliary) electrode
    • A separating funnel
    Answer: A separating funnel
  18. The current that results from the movement of charged analyte ions in the electric field is the:
    • Diffusion current
    • Migration current
    • Residual current
    • Adsorption current
    Answer: Migration current
  19. The Rotating Platinum Electrode is more suitable than the DME for:
    • Reductions at very negative potentials
    • Oxidations at positive potentials
    • Analyzing static solutions
    • Measuring half-wave potentials
    Answer: Oxidations at positive potentials
  20. The ‘m’ term in the Ilkovic equation (id = 607nD¹/²m²/³t¹/⁶C) represents the:
    • Concentration of the analyte
    • Diffusion coefficient
    • Rate of mercury flow from the capillary (mg/s)
    • Drop time in seconds
    Answer: Rate of mercury flow from the capillary (mg/s)
  21. The half-wave potential is a characteristic property of the:
    • Supporting electrolyte
    • Electrode material
    • Electroactive species (analyte)
    • Solvent
    Answer: Electroactive species (analyte)
  22. Why is dissolved oxygen removed from the solution in most polarographic analyses?
    • Oxygen is reduced at the DME and creates interfering waves.
    • Oxygen oxidizes the mercury.
    • Oxygen reacts with the supporting electrolyte.
    • Oxygen is not electroactive.
    Answer: Oxygen is reduced at the DME and creates interfering waves.
  23. The ‘t’ term in the Ilkovic equation represents the:
    • Temperature
    • Time of the experiment
    • Transference number
    • Drop time of the mercury
    Answer: Drop time of the mercury
  24. In quantitative polarography, the height of the wave is a measure of:
    • Concentration
    • Identity of the species
    • Purity of the solvent
    • pH of the solution
    Answer: Concentration
  25. The supporting electrolyte concentration is typically ______ times that of the analyte concentration.
    • 2-5
    • 10-20
    • 50-100
    • The same as
    Answer: 50-100
  26. Which of the following is an application of polarography?
    • Determination of trace metals in alloys and pharmaceuticals.
    • Analysis of vitamins and alkaloids.
    • Study of complex ion formation.
    • All of the above.
    Answer: All of the above.
  27. The current sensitivity of a Rotating Platinum Electrode is generally ______ than that of a DME.
    • lower
    • higher
    • the same
    • not comparable
    Answer: higher
  28. The potential range for a DME is limited on the positive side by the:
    • Oxidation of water
    • Oxidation of the supporting electrolyte
    • Oxidation of mercury itself
    • Reduction of oxygen
    Answer: Oxidation of mercury itself
  29. The ‘n’ term in the Ilkovic equation represents the:
    • Number of ions in the solution
    • Normality of the solution
    • Number of electrons transferred in the electrode reaction
    • Number of mercury drops
    Answer: Number of electrons transferred in the electrode reaction
  30. What is the purpose of the counter electrode (auxiliary electrode) in a three-electrode cell?
    • To measure the potential
    • To provide a constant reference potential
    • To allow current to flow between it and the working electrode
    • To stir the solution
    Answer: To allow current to flow between it and the working electrode
  31. The study of the relationship between current, potential, and concentration is known as:
    • Potentiometry
    • Conductometry
    • Voltammetry
    • Spectroscopy
    Answer: Voltammetry
  32. A substance that is easily reduced at the DME will have a:
    • More positive half-wave potential
    • More negative half-wave potential
    • Half-wave potential of zero
    • Very large diffusion current
    Answer: More positive half-wave potential
  33. The reference electrode commonly used in polarography is the:
    • Dropping mercury electrode
    • Rotating platinum electrode
    • Saturated Calomel Electrode (SCE)
    • Glass electrode
    Answer: Saturated Calomel Electrode (SCE)
  34. The periodic fluctuation in current seen on a polarogram is due to the:
    • Stirring of the solution
    • Growth and fall of the individual mercury drops
    • Alternating current used
    • Depletion of the analyte
    Answer: Growth and fall of the individual mercury drops
  35. The Ilkovic equation is central to ______ polarography.
    • qualitative
    • quantitative
    • both qualitative and quantitative
    • preparative
    Answer: quantitative
  36. Unlike the DME, the surface of a Rotating Platinum Electrode is:
    • Constantly renewed
    • Not renewed and can become contaminated
    • Always liquid
    • Made of an inert gas
    Answer: Not renewed and can become contaminated
  37. The residual current is composed of the faradaic current from impurities and a non-faradaic current called the:
    • Migration current
    • Diffusion current
    • Convection current
    • Condenser (charging) current
    Answer: Condenser (charging) current
  38. The half-wave potential is independent of the:
    • Nature of the electroactive species
    • The supporting electrolyte
    • The complexing agents present
    • Concentration of the analyte
    Answer: Concentration of the analyte
  39. The main advantage of using a micro-electrode like the DME is:
    • Its large size
    • It causes negligible change in the bulk solution concentration
    • It is not easily polarized
    • It is resistant to oxidation
    Answer: It causes negligible change in the bulk solution concentration
  40. The ‘D’ term in the Ilkovic equation represents the:
    • Density of mercury
    • Drop time
    • Diameter of the capillary
    • Diffusion coefficient of the analyte
    Answer: Diffusion coefficient of the analyte
  41. A polarographic maximum is an unwanted peak on the polarogram that can be suppressed by adding:
    • More supporting electrolyte
    • A maximum suppressor like gelatin or Triton X-100
    • An acid or a base
    • A different solvent
    Answer: A maximum suppressor like gelatin or Triton X-100
  42. The potential range of the DME is limited on the negative side by the:
    • Reduction of the supporting electrolyte cation or hydrogen ions
    • Reduction of mercury
    • Oxidation of mercury
    • Reduction of anions
    Answer: Reduction of the supporting electrolyte cation or hydrogen ions
  43. Polarography is a highly sensitive technique suitable for analyzing solutions in the ______ concentration range.
    • 1-2 M
    • 0.1-1 M
    • 10⁻² – 10⁻⁵ M
    • 2 M
    Answer: 10⁻² – 10⁻⁵ M
  44. In a three-electrode system, the potential of the working electrode is measured with respect to the:
    • Counter electrode
    • Reference electrode
    • Solution
    • Cell wall
    Answer: Reference electrode
  45. For quantitative analysis, a calibration curve is typically plotted between the diffusion current and:
    • Half-wave potential
    • Drop time
    • Concentration
    • Temperature
    Answer: Concentration
  46. Compared to the DME, the Rotating Platinum Electrode is better suited for:
    • Continuous monitoring of a solution
    • Analysis of a single drop
    • Use in unstirred solutions
    • Redox reactions only
    Answer: Continuous monitoring of a solution
  47. The supporting electrolyte must be chosen such that it is:
    • Electroactive at the same potential as the analyte
    • Not electroactive within the potential range of the analyte
    • Insoluble in the solvent
    • A strong oxidizing agent
    Answer: Not electroactive within the potential range of the analyte
  48. The analysis of two or more components in a single polarogram is possible if their ______ are sufficiently different.
    • Diffusion currents
    • Concentrations
    • Half-wave potentials
    • Drop times
    Answer: Half-wave potentials
  49. The science of polarography was first developed by:
    • Nernst
    • Ilkovic
    • Heyrovský
    • Faraday
    Answer: Heyrovský
  50. The oscillations on a polarogram can be minimized by using a:
    • Damping circuit in the instrument
    • Larger mercury drop
    • Smaller capillary
    • Higher temperature
    Answer: Damping circuit in the instrument

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