Construction and working of rotating platinum electrode MCQs With Answer

Construction and working of rotating platinum electrode MCQs With Answer

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Introduction

The rotating platinum electrode is a key tool in electrochemistry and pharmaceutical analysis. This introduction explains the construction and working of a rotating platinum electrode (RDE/RPE), highlighting components such as the platinum disk, shaft, insulating sleeve, motor, and electrode housing. It covers hydrodynamic voltammetry, mass transport control, diffusion layer behavior, and the Levich and Koutecky–Levich relationships used to extract kinetic and diffusion parameters. Emphasis is placed on rotation speed (rpm), limiting current, convective diffusion, and practical maintenance like polishing and cleaning. This concise, keyword-rich overview is tailored for B.Pharm students studying electrochemical methods and instrumental analysis. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. What is the most common material used for the active surface of a rotating platinum electrode?

  • Glassy carbon
  • Gold foil
  • Platinum disk
  • Silver plate

Correct Answer: Platinum disk

Q2. Which component directly controls the hydrodynamic flow at the electrode surface?

  • Reference electrode
  • Rotation motor
  • Potentiostat
  • Salt bridge

Correct Answer: Rotation motor

Q3. In RDE experiments, increasing rotation speed primarily affects which parameter?

  • Solution pH
  • Diffusion layer thickness
  • E° of the redox couple
  • Double layer capacitance

Correct Answer: Diffusion layer thickness

Q4. The Levich equation describes the relationship between limiting current and which variable?

  • Applied potential
  • Square root of rotation rate (ω^1/2)
  • Solution dielectric constant
  • Electrode temperature

Correct Answer: Square root of rotation rate (ω^1/2)

Q5. Which term appears in the Levich equation for limiting current: I_L = 0.62 n F A D^(2/3) ν^(-1/6) ω^(1/2) C?

  • 0.62 (a numeric constant)
  • 0.08 (a numeric constant)
  • 1.23 (a numeric constant)
  • 0.005 (a numeric constant)

Correct Answer: 0.62 (a numeric constant)

Q6. For a first-order electrode process under mass-transport control at an RDE, the limiting current is proportional to:

  • ω^2 (rotation rate squared)
  • ω (rotation rate)
  • ω^(1/2) (square root of rotation rate)
  • log(ω) (logarithm of rotation rate)

Correct Answer: ω^(1/2) (square root of rotation rate)

Q7. Which experimental approach combines an RDE with a ring electrode to detect reaction products?

  • Stationary electrode voltammetry
  • Rotating ring-disk electrode (RRDE)
  • Punch-through electrode setup
  • Double reference cell

Correct Answer: Rotating ring-disk electrode (RRDE)

Q8. The Koutecky–Levich equation is used to separate which two contributions to current?

  • Capacitive and inductive currents
  • Faradaic kinetic and mass-transport limiting currents
  • Oxidative and reductive potentials
  • AC and DC components

Correct Answer: Faradaic kinetic and mass-transport limiting currents

Q9. Which property of platinum makes it a preferred disk material for RDE in pharmaceutical electroanalysis?

  • High solubility in aqueous media
  • Excellent catalytic activity and corrosion resistance
  • Magnetic behavior
  • Transparent optical properties

Correct Answer: Excellent catalytic activity and corrosion resistance

Q10. Typical rotation speeds used in RDE experiments for analyte diffusion studies are in which range?

  • 0.1–1 rpm
  • 10–50 rpm
  • 100–10,000 rpm
  • 20,000–100,000 rpm

Correct Answer: 100–10,000 rpm

Q11. What does a Levich plot display on the y-axis vs. ω^1/2 on the x-axis?

  • Log(current) vs. ω
  • Limiting current (I_L) vs. ω^1/2
  • Potential vs. ω^1/2
  • Capacitance vs. ω

Correct Answer: Limiting current (I_L) vs. ω^1/2

Q12. Which factor is NOT part of the Levich equation parameters?

  • Diffusion coefficient (D)
  • Viscosity (ν)
  • Solution concentration (C)
  • Electrode thickness

Correct Answer: Electrode thickness

Q13. Decreasing the diffusion layer thickness at the rotating electrode increases which of the following?

  • Limiting current
  • Solution pH
  • Cell resistance
  • Electrode surface roughness

Correct Answer: Limiting current

Q14. Which cleaning method is commonly used to restore a platinum disk surface before measurements?

  • Polishing with alumina slurry and rinsing
  • Soaking in oil
  • Coating with organic film
  • Heating to 700°C in air

Correct Answer: Polishing with alumina slurry and rinsing

Q15. The boundary layer thickness at an RDE scales with rotation rate as:

  • δ ∝ ω^(1/2)
  • δ ∝ ω^(-1/2)
  • δ ∝ ω
  • δ independent of ω

Correct Answer: δ ∝ ω^(-1/2)

Q16. For kinetic studies using RDE, which plot is commonly used to determine the standard rate constant?

  • Nyquist plot from EIS
  • Koutecky–Levich plot (1/I vs. ω^(-1/2))
  • Tafel plot of potential vs. log(current)
  • Absorbance vs. wavelength

Correct Answer: Koutecky–Levich plot (1/I vs. ω^(-1/2))

Q17. Which of the following best describes hydrodynamic voltammetry with an RDE?

  • Measurements under strictly diffusive transport only
  • Control of convective transport by rotation to study mass transport and kinetics
  • Electrochemical impedance solely at DC
  • Thermogravimetric analysis coupled to potentiometry

Correct Answer: Control of convective transport by rotation to study mass transport and kinetics

Q18. In pharmaceutical analysis, rotating platinum electrodes are particularly useful for studying:

  • Solid-state nuclear magnetic resonance
  • Redox behavior and reaction mechanisms of active pharmaceutical ingredients
  • Melting point determination
  • X-ray diffraction of crystals

Correct Answer: Redox behavior and reaction mechanisms of active pharmaceutical ingredients

Q19. Which experimental artifact can result from too-high rotation speed or misalignment of the RDE?

  • Enhanced signal-to-noise ratio only
  • Vibration and noisy current responses
  • Lower mass transport to the electrode
  • Automatic stabilization of baseline

Correct Answer: Vibration and noisy current responses

Q20. What is the role of the insulating sleeve in a rotating platinum electrode assembly?

  • To catalyze redox reactions
  • To electrically isolate the shaft and define the exposed disk area
  • To increase solution conductivity
  • To measure solution temperature

Correct Answer: To electrically isolate the shaft and define the exposed disk area

Q21. Which parameter must be known to calculate diffusion coefficient using Levich analysis?

  • Solution color
  • Electrode surface roughness only
  • Limiting current, rotation rate, concentration, kinematic viscosity, electrode area
  • Atmospheric pressure only

Correct Answer: Limiting current, rotation rate, concentration, kinematic viscosity, electrode area

Q22. When studying a reversible electron transfer at RDE, the observed current-potential curve shape is primarily controlled by:

  • Mass transport and Nernstian equilibrium at the surface
  • Magnetic fields in the lab
  • The UV absorbance of the analyte
  • The light intensity on the electrode

Correct Answer: Mass transport and Nernstian equilibrium at the surface

Q23. Which safety or maintenance practice is recommended for rotating platinum electrodes?

  • Polish with coarse sandpaper without rinsing
  • Operate without checking alignment to save time
  • Regularly inspect shaft alignment and clean the disk to avoid damage
  • Immerse the motor in electrolyte for cooling

Correct Answer: Regularly inspect shaft alignment and clean the disk to avoid damage

Q24. In an RRDE experiment, the ring current often provides information about:

  • Light scattering by particles
  • Products or intermediates formed at the disk that are detected at the ring
  • Solution viscosity only
  • Magnetic susceptibility of analytes

Correct Answer: Products or intermediates formed at the disk that are detected at the ring

Q25. Which type of flow regime near the rotating disk is assumed by the Levich derivation?

  • Turbulent chaotic flow throughout
  • Lamin ar boundary layer with steady convective flow
  • Pure molecular diffusion with zero convection
  • Intermittent pulsatile flow

Correct Answer: Lamin ar boundary layer with steady convective flow

Q26. Which unit is commonly used for rotation rate in the Levich equation when expressed as angular velocity?

  • Kelvin (K)
  • Radians per second (rad s^-1) or rpm converted to ω
  • Mol L^-1
  • Farads

Correct Answer: Radians per second (rad s^-1) or rpm converted to ω

Q27. The presence of convection in RDE experiments helps to:

  • Eliminate all kinetic control so only diffusion matters
  • Enhance reproducibility by controlling mass transport and thinning the diffusion layer
  • Increase solution conductivity dramatically
  • Prevent electron transfer reactions

Correct Answer: Enhance reproducibility by controlling mass transport and thinning the diffusion layer

Q28. Which measurement is least appropriate to perform with a rotating platinum electrode?

  • Determination of diffusion coefficient
  • Study of fast heterogeneous electron transfer kinetics
  • DC conductivity of a solid pellet
  • Investigation of reaction intermediates with RRDE

Correct Answer: DC conductivity of a solid pellet

Q29. If the experimentally determined Levich slope is lower than theoretical, a possible cause is:

  • Perfect electrode polishing
  • Convection-free ideal behavior
  • Surface fouling or incorrect estimate of electrode area
  • Absence of analyte

Correct Answer: Surface fouling or incorrect estimate of electrode area

Q30. For quantitative analysis in pharmaceutical samples using RDE, which practice improves accuracy?

  • Neglecting to calibrate rotation speed
  • Using unfiltered reagents only
  • Calibrating electrode area, controlling rpm, and cleaning the platinum disk between runs
  • Running at random potentials each time

Correct Answer: Calibrating electrode area, controlling rpm, and cleaning the platinum disk between runs

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