Principle of polarography MCQs With Answer

Principle of polarography MCQs With Answer
Polarography is an electroanalytical method vital in pharmaceutical analysis that measures current as a function of applied potential at a dropping mercury electrode. The principle of polarography is based on diffusion-controlled reduction or oxidation at a renewable mercury surface, producing characteristic polarographic waves described by the Ilkovic equation, diffusion current and half-wave potential (E1/2). Key concepts for B. Pharm students include supporting electrolyte, electrode kinetics (reversible vs irreversible), charging current, pulse techniques, interferences (e.g., oxygen), and practical sample considerations. This set emphasizes theory, instrumentation and analytical applications relevant to drug analysis. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. What is the basic principle of polarography?

• Measurement of current as a function of applied potential using a dropping mercury electrode
• Measurement of solution conductivity at constant potential
• Measurement of pH changes during potentiometric titration
• Measurement of absorbance versus wavelength in UV spectroscopy

Correct Answer: Measurement of current as a function of applied potential using a dropping mercury electrode

Q2. What is the main advantage of a dropping mercury electrode (DME) in polarography?

• Provides a renewable, reproducible fresh surface for each measurement
• Is solid and immune to film formation
• Has a very narrow electrochemical window
• Prevents any adsorption of analyte

Correct Answer: Provides a renewable, reproducible fresh surface for each measurement

Q3. According to the Ilkovic equation, which of the following directly affects the diffusion current?

• Analyte concentration
• Solution color
• Electrode thickness
• Optical transparency of the cell

Correct Answer: Analyte concentration

Q4. The half-wave potential (E1/2) in polarography is most useful for:

• Identifying the electrochemical identity (redox potential) of an analyte
• Measuring solution viscosity
• Determining the exact drop time of mercury only
• Calibrating the pH electrode

Correct Answer: Identifying the electrochemical identity (redox potential) of an analyte

Q5. Why is a supporting electrolyte used in polarographic measurements?

• To minimize migration of analyte ions and ensure diffusion control
• To react chemically with the analyte and form a precipitate
• To increase the optical absorbance of the solution
• To prevent formation of mercury drops

Correct Answer: To minimize migration of analyte ions and ensure diffusion control

Q6. A sigmoidal polarographic wave typically indicates which controlling process?

• Diffusion-controlled electrochemical reaction
• Convection-controlled reaction
• Purely resistive behavior with no mass transport
• Photon-induced current

Correct Answer: Diffusion-controlled electrochemical reaction

Q7. A reversible polarographic system is characterized by which statement?

• Electron transfer is fast enough to maintain Nernst equilibrium at the electrode surface
• Electron transfer is so slow that no wave appears
• The system is independent of diffusion processes
• The electrode surface is permanently passivated

Correct Answer: Electron transfer is fast enough to maintain Nernst equilibrium at the electrode surface

Q8. Which current component in polarography is due to charging and discharging of the electrode double layer?

• Capacitive (charging) current
• Faradaic diffusion current
• Photocurrent
• Conduction current through the reference electrode

Correct Answer: Capacitive (charging) current

Q9. The limiting diffusion current observed in a polarogram is:

• Independent of applied potential in the plateau region and proportional to concentration
• Increasing indefinitely with applied potential
• Dependent only on solution color
• Zero for all redox-active species

Correct Answer: Independent of applied potential in the plateau region and proportional to concentration

Q10. One major advantage of pulse polarography over direct current polarography is:

• Significant reduction of capacitive (charging) current and improved sensitivity
• Complete elimination of diffusion control
• Ability to analyze gases without deoxygenation
• Requirement of much larger sample volumes

Correct Answer: Significant reduction of capacitive (charging) current and improved sensitivity

Q11. How does pH commonly affect the half-wave potential (E1/2) in polarographic reduction of species involving protons?

• E1/2 shifts depending on proton concentration; pH changes alter E1/2
• pH has no effect on any polarographic measurements
• E1/2 becomes independent of electrode material only
• E1/2 only depends on light intensity

Correct Answer: E1/2 shifts depending on proton concentration; pH changes alter E1/2

Q12. Why is deaeration (removal of dissolved oxygen) often necessary before polarographic analysis?

• Dissolved oxygen is electroactive and produces interfering reduction currents
• Oxygen increases the viscosity making measurements impossible
• Oxygen reacts with mercury to form a protective oxide layer
• Oxygen prevents the formation of a supporting electrolyte

Correct Answer: Dissolved oxygen is electroactive and produces interfering reduction currents

Q13. Which reference electrode is commonly used in polarographic measurements?

• Saturated calomel electrode (SCE)
• Glass pH electrode
• Fluoride ion selective electrode
• Optical oxygen sensor

Correct Answer: Saturated calomel electrode (SCE)

Q14. Why is mercury a preferred material for the polarographic working electrode?

• It offers a wide cathodic potential window and a renewable, smooth surface
• It is cheaper than all other electrode materials
• It is an insulator that prevents current flow
• It absorbs all analytes preventing reaction

Correct Answer: It offers a wide cathodic potential window and a renewable, smooth surface

Q15. A peak-shaped polarographic response rather than a sigmoidal wave often indicates:

• Significant adsorption of analyte on the mercury surface
• Complete absence of analyte
• That the measurement was made without a reference electrode
• That the solution temperature is below freezing

Correct Answer: Significant adsorption of analyte on the mercury surface

Q16. The Sliding Mercury Drop Electrode (SMDE) provides which main advantage over the classic DME?

• Better control of drop size and improved reproducibility
• It eliminates the need for supporting electrolyte
• It is made of solid mercury alloy
• It operates without any potential control

Correct Answer: Better control of drop size and improved reproducibility

Q17. Which parameters are explicitly included in the Ilkovic equation for diffusion current?

• Analyte concentration, diffusion coefficient and drop time (or mercury flow rate)
• Solution color, pH meter calibration and electrode polish
• Optical path length, refractive index and absorbance
• Temperature only and nothing else

Correct Answer: Analyte concentration, diffusion coefficient and drop time (or mercury flow rate)

Q18. Which quantitative approach is commonly used in polarographic analysis to overcome matrix effects in pharmaceutical samples?

• Standard addition method
• Direct colorimetric estimation without calibration
• Estimating by eye using comparison tubes
• Using an unrelated internal standard only

Correct Answer: Standard addition method

Q19. Differential pulse polarography improves sensitivity by:

• Superimposing small pulses on a potential ramp and measuring the difference in current to reduce background
• Holding the potential constant and measuring at random times
• Using continuous illumination to excite analytes
• Eliminating the need for a reference electrode

Correct Answer: Superimposing small pulses on a potential ramp and measuring the difference in current to reduce background

Q20. Which current component is most directly used for quantitation in polarography?

• Diffusion (faradaic) current
• Capacitive charging current
• Photocurrent caused by ambient light
• Reference electrode leakage current

Correct Answer: Diffusion (faradaic) current

Q21. For a reversible one-electron reduction, the half-wave potential (E1/2) is primarily characteristic of:

• The redox couple and not dependent on analyte concentration
• The ambient light intensity in the lab
• The color of the mercury drop
• The stirring speed only

Correct Answer: The redox couple and not dependent on analyte concentration

Q22. To resolve two overlapping polarographic waves from similar species, a practical strategy is to:

• Add a complexing ligand or change pH to shift one species’ E1/2
• Ignore one species and report the combined signal
• Decrease supporting electrolyte concentration to zero
• Use a colorimetric reagent instead of electrochemistry

Correct Answer: Add a complexing ligand or change pH to shift one species’ E1/2

Q23. The recorded plot of current versus applied potential in polarography is called a:

• Polarogram
• Chromatogram
• Spectrum
• Thermogram

Correct Answer: Polarogram

Q24. Adsorptive effects on the mercury surface commonly lead to which analytical consequence?

• Peak-shaped responses and non-Faradaic behavior complicating quantitation
• Complete elimination of diffusion current making analysis trivial
• Automatic separation of analytes without intervention
• Instant equilibrium with no current measured

Correct Answer: Peak-shaped responses and non-Faradaic behavior complicating quantitation

Q25. Polarography is best classified as a subset of which broader electrochemical technique?

• Voltammetry
• Spectrophotometry
• Thermogravimetry
• Gas chromatography

Correct Answer: Voltammetry

Q26. Which operational practice helps minimize drop-to-drop variability in DME polarography?

• Maintaining a constant mercury flow rate or controlled drop time
• Varying the mercury flow randomly during measurement
• Using no supporting electrolyte at all
• Changing the reference electrode frequently during a single run

Correct Answer: Maintaining a constant mercury flow rate or controlled drop time

Q27. If a species shows a half-wave potential that shifts to more negative values under otherwise identical conditions, this indicates:

• The species requires a more negative potential and is harder to reduce
• The species is being oxidized more easily
• The solution has become optically opaque
• The electrode has become positively charged only

Correct Answer: The species requires a more negative potential and is harder to reduce

Q28. A significant practical limitation of classical polarography in pharmaceutical labs is:

• Use of mercury, which poses toxicity and disposal concerns
• Inability to detect any inorganic ions
• Requirement for extremely large sample volumes only
• Complete incompatibility with aqueous solutions

Correct Answer: Use of mercury, which poses toxicity and disposal concerns

Q29. Which technique couples preconcentration with stripping for trace metal analysis related to polarography?

• Anodic stripping voltammetry (ASV)
• Colorimetric titration
• Reversed-phase HPLC
• Gravimetric analysis only

Correct Answer: Anodic stripping voltammetry (ASV)

Q30. In pharmaceutical polarographic analysis, why is complexation used as a separation strategy?

• Complexation shifts E1/2 of one component allowing resolution of overlapping waves
• Complexation increases the solution viscosity to prevent diffusion
• Complexation always eliminates all electrochemical signals
• Complexation makes the analyte invisible to the electrode

Correct Answer: Complexation shifts E1/2 of one component allowing resolution of overlapping waves

G S Sachin

I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.

Mail- Sachin@pharmacyfreak.com